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Linux/block/bfq-iosched.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  * Budget Fair Queueing (BFQ) I/O scheduler.
  4  *
  5  * Based on ideas and code from CFQ:
  6  * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
  7  *
  8  * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
  9  *                    Paolo Valente <paolo.valente@unimore.it>
 10  *
 11  * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
 12  *                    Arianna Avanzini <avanzini@google.com>
 13  *
 14  * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
 15  *
 16  * BFQ is a proportional-share I/O scheduler, with some extra
 17  * low-latency capabilities. BFQ also supports full hierarchical
 18  * scheduling through cgroups. Next paragraphs provide an introduction
 19  * on BFQ inner workings. Details on BFQ benefits, usage and
 20  * limitations can be found in Documentation/block/bfq-iosched.rst.
 21  *
 22  * BFQ is a proportional-share storage-I/O scheduling algorithm based
 23  * on the slice-by-slice service scheme of CFQ. But BFQ assigns
 24  * budgets, measured in number of sectors, to processes instead of
 25  * time slices. The device is not granted to the in-service process
 26  * for a given time slice, but until it has exhausted its assigned
 27  * budget. This change from the time to the service domain enables BFQ
 28  * to distribute the device throughput among processes as desired,
 29  * without any distortion due to throughput fluctuations, or to device
 30  * internal queueing. BFQ uses an ad hoc internal scheduler, called
 31  * B-WF2Q+, to schedule processes according to their budgets. More
 32  * precisely, BFQ schedules queues associated with processes. Each
 33  * process/queue is assigned a user-configurable weight, and B-WF2Q+
 34  * guarantees that each queue receives a fraction of the throughput
 35  * proportional to its weight. Thanks to the accurate policy of
 36  * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
 37  * processes issuing sequential requests (to boost the throughput),
 38  * and yet guarantee a low latency to interactive and soft real-time
 39  * applications.
 40  *
 41  * In particular, to provide these low-latency guarantees, BFQ
 42  * explicitly privileges the I/O of two classes of time-sensitive
 43  * applications: interactive and soft real-time. In more detail, BFQ
 44  * behaves this way if the low_latency parameter is set (default
 45  * configuration). This feature enables BFQ to provide applications in
 46  * these classes with a very low latency.
 47  *
 48  * To implement this feature, BFQ constantly tries to detect whether
 49  * the I/O requests in a bfq_queue come from an interactive or a soft
 50  * real-time application. For brevity, in these cases, the queue is
 51  * said to be interactive or soft real-time. In both cases, BFQ
 52  * privileges the service of the queue, over that of non-interactive
 53  * and non-soft-real-time queues. This privileging is performed,
 54  * mainly, by raising the weight of the queue. So, for brevity, we
 55  * call just weight-raising periods the time periods during which a
 56  * queue is privileged, because deemed interactive or soft real-time.
 57  *
 58  * The detection of soft real-time queues/applications is described in
 59  * detail in the comments on the function
 60  * bfq_bfqq_softrt_next_start. On the other hand, the detection of an
 61  * interactive queue works as follows: a queue is deemed interactive
 62  * if it is constantly non empty only for a limited time interval,
 63  * after which it does become empty. The queue may be deemed
 64  * interactive again (for a limited time), if it restarts being
 65  * constantly non empty, provided that this happens only after the
 66  * queue has remained empty for a given minimum idle time.
 67  *
 68  * By default, BFQ computes automatically the above maximum time
 69  * interval, i.e., the time interval after which a constantly
 70  * non-empty queue stops being deemed interactive. Since a queue is
 71  * weight-raised while it is deemed interactive, this maximum time
 72  * interval happens to coincide with the (maximum) duration of the
 73  * weight-raising for interactive queues.
 74  *
 75  * Finally, BFQ also features additional heuristics for
 76  * preserving both a low latency and a high throughput on NCQ-capable,
 77  * rotational or flash-based devices, and to get the job done quickly
 78  * for applications consisting in many I/O-bound processes.
 79  *
 80  * NOTE: if the main or only goal, with a given device, is to achieve
 81  * the maximum-possible throughput at all times, then do switch off
 82  * all low-latency heuristics for that device, by setting low_latency
 83  * to 0.
 84  *
 85  * BFQ is described in [1], where also a reference to the initial,
 86  * more theoretical paper on BFQ can be found. The interested reader
 87  * can find in the latter paper full details on the main algorithm, as
 88  * well as formulas of the guarantees and formal proofs of all the
 89  * properties.  With respect to the version of BFQ presented in these
 90  * papers, this implementation adds a few more heuristics, such as the
 91  * ones that guarantee a low latency to interactive and soft real-time
 92  * applications, and a hierarchical extension based on H-WF2Q+.
 93  *
 94  * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
 95  * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
 96  * with O(log N) complexity derives from the one introduced with EEVDF
 97  * in [3].
 98  *
 99  * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
100  *     Scheduler", Proceedings of the First Workshop on Mobile System
101  *     Technologies (MST-2015), May 2015.
102  *     http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
103  *
104  * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
105  *     Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
106  *     Oct 1997.
107  *
108  * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
109  *
110  * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
111  *     First: A Flexible and Accurate Mechanism for Proportional Share
112  *     Resource Allocation", technical report.
113  *
114  * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
115  */
116 #include <linux/module.h>
117 #include <linux/slab.h>
118 #include <linux/blkdev.h>
119 #include <linux/cgroup.h>
120 #include <linux/elevator.h>
121 #include <linux/ktime.h>
122 #include <linux/rbtree.h>
123 #include <linux/ioprio.h>
124 #include <linux/sbitmap.h>
125 #include <linux/delay.h>
126 #include <linux/backing-dev.h>
127 
128 #include "blk.h"
129 #include "blk-mq.h"
130 #include "blk-mq-tag.h"
131 #include "blk-mq-sched.h"
132 #include "bfq-iosched.h"
133 #include "blk-wbt.h"
134 
135 #define BFQ_BFQQ_FNS(name)                                              \
136 void bfq_mark_bfqq_##name(struct bfq_queue *bfqq)                       \
137 {                                                                       \
138         __set_bit(BFQQF_##name, &(bfqq)->flags);                        \
139 }                                                                       \
140 void bfq_clear_bfqq_##name(struct bfq_queue *bfqq)                      \
141 {                                                                       \
142         __clear_bit(BFQQF_##name, &(bfqq)->flags);              \
143 }                                                                       \
144 int bfq_bfqq_##name(const struct bfq_queue *bfqq)                       \
145 {                                                                       \
146         return test_bit(BFQQF_##name, &(bfqq)->flags);          \
147 }
148 
149 BFQ_BFQQ_FNS(just_created);
150 BFQ_BFQQ_FNS(busy);
151 BFQ_BFQQ_FNS(wait_request);
152 BFQ_BFQQ_FNS(non_blocking_wait_rq);
153 BFQ_BFQQ_FNS(fifo_expire);
154 BFQ_BFQQ_FNS(has_short_ttime);
155 BFQ_BFQQ_FNS(sync);
156 BFQ_BFQQ_FNS(IO_bound);
157 BFQ_BFQQ_FNS(in_large_burst);
158 BFQ_BFQQ_FNS(coop);
159 BFQ_BFQQ_FNS(split_coop);
160 BFQ_BFQQ_FNS(softrt_update);
161 BFQ_BFQQ_FNS(has_waker);
162 #undef BFQ_BFQQ_FNS                                             \
163 
164 /* Expiration time of sync (0) and async (1) requests, in ns. */
165 static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
166 
167 /* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
168 static const int bfq_back_max = 16 * 1024;
169 
170 /* Penalty of a backwards seek, in number of sectors. */
171 static const int bfq_back_penalty = 2;
172 
173 /* Idling period duration, in ns. */
174 static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
175 
176 /* Minimum number of assigned budgets for which stats are safe to compute. */
177 static const int bfq_stats_min_budgets = 194;
178 
179 /* Default maximum budget values, in sectors and number of requests. */
180 static const int bfq_default_max_budget = 16 * 1024;
181 
182 /*
183  * When a sync request is dispatched, the queue that contains that
184  * request, and all the ancestor entities of that queue, are charged
185  * with the number of sectors of the request. In contrast, if the
186  * request is async, then the queue and its ancestor entities are
187  * charged with the number of sectors of the request, multiplied by
188  * the factor below. This throttles the bandwidth for async I/O,
189  * w.r.t. to sync I/O, and it is done to counter the tendency of async
190  * writes to steal I/O throughput to reads.
191  *
192  * The current value of this parameter is the result of a tuning with
193  * several hardware and software configurations. We tried to find the
194  * lowest value for which writes do not cause noticeable problems to
195  * reads. In fact, the lower this parameter, the stabler I/O control,
196  * in the following respect.  The lower this parameter is, the less
197  * the bandwidth enjoyed by a group decreases
198  * - when the group does writes, w.r.t. to when it does reads;
199  * - when other groups do reads, w.r.t. to when they do writes.
200  */
201 static const int bfq_async_charge_factor = 3;
202 
203 /* Default timeout values, in jiffies, approximating CFQ defaults. */
204 const int bfq_timeout = HZ / 8;
205 
206 /*
207  * Time limit for merging (see comments in bfq_setup_cooperator). Set
208  * to the slowest value that, in our tests, proved to be effective in
209  * removing false positives, while not causing true positives to miss
210  * queue merging.
211  *
212  * As can be deduced from the low time limit below, queue merging, if
213  * successful, happens at the very beginning of the I/O of the involved
214  * cooperating processes, as a consequence of the arrival of the very
215  * first requests from each cooperator.  After that, there is very
216  * little chance to find cooperators.
217  */
218 static const unsigned long bfq_merge_time_limit = HZ/10;
219 
220 static struct kmem_cache *bfq_pool;
221 
222 /* Below this threshold (in ns), we consider thinktime immediate. */
223 #define BFQ_MIN_TT              (2 * NSEC_PER_MSEC)
224 
225 /* hw_tag detection: parallel requests threshold and min samples needed. */
226 #define BFQ_HW_QUEUE_THRESHOLD  3
227 #define BFQ_HW_QUEUE_SAMPLES    32
228 
229 #define BFQQ_SEEK_THR           (sector_t)(8 * 100)
230 #define BFQQ_SECT_THR_NONROT    (sector_t)(2 * 32)
231 #define BFQ_RQ_SEEKY(bfqd, last_pos, rq) \
232         (get_sdist(last_pos, rq) >                      \
233          BFQQ_SEEK_THR &&                               \
234          (!blk_queue_nonrot(bfqd->queue) ||             \
235           blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT))
236 #define BFQQ_CLOSE_THR          (sector_t)(8 * 1024)
237 #define BFQQ_SEEKY(bfqq)        (hweight32(bfqq->seek_history) > 19)
238 /*
239  * Sync random I/O is likely to be confused with soft real-time I/O,
240  * because it is characterized by limited throughput and apparently
241  * isochronous arrival pattern. To avoid false positives, queues
242  * containing only random (seeky) I/O are prevented from being tagged
243  * as soft real-time.
244  */
245 #define BFQQ_TOTALLY_SEEKY(bfqq)        (bfqq->seek_history == -1)
246 
247 /* Min number of samples required to perform peak-rate update */
248 #define BFQ_RATE_MIN_SAMPLES    32
249 /* Min observation time interval required to perform a peak-rate update (ns) */
250 #define BFQ_RATE_MIN_INTERVAL   (300*NSEC_PER_MSEC)
251 /* Target observation time interval for a peak-rate update (ns) */
252 #define BFQ_RATE_REF_INTERVAL   NSEC_PER_SEC
253 
254 /*
255  * Shift used for peak-rate fixed precision calculations.
256  * With
257  * - the current shift: 16 positions
258  * - the current type used to store rate: u32
259  * - the current unit of measure for rate: [sectors/usec], or, more precisely,
260  *   [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
261  * the range of rates that can be stored is
262  * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
263  * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
264  * [15, 65G] sectors/sec
265  * Which, assuming a sector size of 512B, corresponds to a range of
266  * [7.5K, 33T] B/sec
267  */
268 #define BFQ_RATE_SHIFT          16
269 
270 /*
271  * When configured for computing the duration of the weight-raising
272  * for interactive queues automatically (see the comments at the
273  * beginning of this file), BFQ does it using the following formula:
274  * duration = (ref_rate / r) * ref_wr_duration,
275  * where r is the peak rate of the device, and ref_rate and
276  * ref_wr_duration are two reference parameters.  In particular,
277  * ref_rate is the peak rate of the reference storage device (see
278  * below), and ref_wr_duration is about the maximum time needed, with
279  * BFQ and while reading two files in parallel, to load typical large
280  * applications on the reference device (see the comments on
281  * max_service_from_wr below, for more details on how ref_wr_duration
282  * is obtained).  In practice, the slower/faster the device at hand
283  * is, the more/less it takes to load applications with respect to the
284  * reference device.  Accordingly, the longer/shorter BFQ grants
285  * weight raising to interactive applications.
286  *
287  * BFQ uses two different reference pairs (ref_rate, ref_wr_duration),
288  * depending on whether the device is rotational or non-rotational.
289  *
290  * In the following definitions, ref_rate[0] and ref_wr_duration[0]
291  * are the reference values for a rotational device, whereas
292  * ref_rate[1] and ref_wr_duration[1] are the reference values for a
293  * non-rotational device. The reference rates are not the actual peak
294  * rates of the devices used as a reference, but slightly lower
295  * values. The reason for using slightly lower values is that the
296  * peak-rate estimator tends to yield slightly lower values than the
297  * actual peak rate (it can yield the actual peak rate only if there
298  * is only one process doing I/O, and the process does sequential
299  * I/O).
300  *
301  * The reference peak rates are measured in sectors/usec, left-shifted
302  * by BFQ_RATE_SHIFT.
303  */
304 static int ref_rate[2] = {14000, 33000};
305 /*
306  * To improve readability, a conversion function is used to initialize
307  * the following array, which entails that the array can be
308  * initialized only in a function.
309  */
310 static int ref_wr_duration[2];
311 
312 /*
313  * BFQ uses the above-detailed, time-based weight-raising mechanism to
314  * privilege interactive tasks. This mechanism is vulnerable to the
315  * following false positives: I/O-bound applications that will go on
316  * doing I/O for much longer than the duration of weight
317  * raising. These applications have basically no benefit from being
318  * weight-raised at the beginning of their I/O. On the opposite end,
319  * while being weight-raised, these applications
320  * a) unjustly steal throughput to applications that may actually need
321  * low latency;
322  * b) make BFQ uselessly perform device idling; device idling results
323  * in loss of device throughput with most flash-based storage, and may
324  * increase latencies when used purposelessly.
325  *
326  * BFQ tries to reduce these problems, by adopting the following
327  * countermeasure. To introduce this countermeasure, we need first to
328  * finish explaining how the duration of weight-raising for
329  * interactive tasks is computed.
330  *
331  * For a bfq_queue deemed as interactive, the duration of weight
332  * raising is dynamically adjusted, as a function of the estimated
333  * peak rate of the device, so as to be equal to the time needed to
334  * execute the 'largest' interactive task we benchmarked so far. By
335  * largest task, we mean the task for which each involved process has
336  * to do more I/O than for any of the other tasks we benchmarked. This
337  * reference interactive task is the start-up of LibreOffice Writer,
338  * and in this task each process/bfq_queue needs to have at most ~110K
339  * sectors transferred.
340  *
341  * This last piece of information enables BFQ to reduce the actual
342  * duration of weight-raising for at least one class of I/O-bound
343  * applications: those doing sequential or quasi-sequential I/O. An
344  * example is file copy. In fact, once started, the main I/O-bound
345  * processes of these applications usually consume the above 110K
346  * sectors in much less time than the processes of an application that
347  * is starting, because these I/O-bound processes will greedily devote
348  * almost all their CPU cycles only to their target,
349  * throughput-friendly I/O operations. This is even more true if BFQ
350  * happens to be underestimating the device peak rate, and thus
351  * overestimating the duration of weight raising. But, according to
352  * our measurements, once transferred 110K sectors, these processes
353  * have no right to be weight-raised any longer.
354  *
355  * Basing on the last consideration, BFQ ends weight-raising for a
356  * bfq_queue if the latter happens to have received an amount of
357  * service at least equal to the following constant. The constant is
358  * set to slightly more than 110K, to have a minimum safety margin.
359  *
360  * This early ending of weight-raising reduces the amount of time
361  * during which interactive false positives cause the two problems
362  * described at the beginning of these comments.
363  */
364 static const unsigned long max_service_from_wr = 120000;
365 
366 #define RQ_BIC(rq)              icq_to_bic((rq)->elv.priv[0])
367 #define RQ_BFQQ(rq)             ((rq)->elv.priv[1])
368 
369 struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
370 {
371         return bic->bfqq[is_sync];
372 }
373 
374 void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
375 {
376         bic->bfqq[is_sync] = bfqq;
377 }
378 
379 struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
380 {
381         return bic->icq.q->elevator->elevator_data;
382 }
383 
384 /**
385  * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
386  * @icq: the iocontext queue.
387  */
388 static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
389 {
390         /* bic->icq is the first member, %NULL will convert to %NULL */
391         return container_of(icq, struct bfq_io_cq, icq);
392 }
393 
394 /**
395  * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
396  * @bfqd: the lookup key.
397  * @ioc: the io_context of the process doing I/O.
398  * @q: the request queue.
399  */
400 static struct bfq_io_cq *bfq_bic_lookup(struct bfq_data *bfqd,
401                                         struct io_context *ioc,
402                                         struct request_queue *q)
403 {
404         if (ioc) {
405                 unsigned long flags;
406                 struct bfq_io_cq *icq;
407 
408                 spin_lock_irqsave(&q->queue_lock, flags);
409                 icq = icq_to_bic(ioc_lookup_icq(ioc, q));
410                 spin_unlock_irqrestore(&q->queue_lock, flags);
411 
412                 return icq;
413         }
414 
415         return NULL;
416 }
417 
418 /*
419  * Scheduler run of queue, if there are requests pending and no one in the
420  * driver that will restart queueing.
421  */
422 void bfq_schedule_dispatch(struct bfq_data *bfqd)
423 {
424         if (bfqd->queued != 0) {
425                 bfq_log(bfqd, "schedule dispatch");
426                 blk_mq_run_hw_queues(bfqd->queue, true);
427         }
428 }
429 
430 #define bfq_class_idle(bfqq)    ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
431 
432 #define bfq_sample_valid(samples)       ((samples) > 80)
433 
434 /*
435  * Lifted from AS - choose which of rq1 and rq2 that is best served now.
436  * We choose the request that is closer to the head right now.  Distance
437  * behind the head is penalized and only allowed to a certain extent.
438  */
439 static struct request *bfq_choose_req(struct bfq_data *bfqd,
440                                       struct request *rq1,
441                                       struct request *rq2,
442                                       sector_t last)
443 {
444         sector_t s1, s2, d1 = 0, d2 = 0;
445         unsigned long back_max;
446 #define BFQ_RQ1_WRAP    0x01 /* request 1 wraps */
447 #define BFQ_RQ2_WRAP    0x02 /* request 2 wraps */
448         unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
449 
450         if (!rq1 || rq1 == rq2)
451                 return rq2;
452         if (!rq2)
453                 return rq1;
454 
455         if (rq_is_sync(rq1) && !rq_is_sync(rq2))
456                 return rq1;
457         else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
458                 return rq2;
459         if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
460                 return rq1;
461         else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
462                 return rq2;
463 
464         s1 = blk_rq_pos(rq1);
465         s2 = blk_rq_pos(rq2);
466 
467         /*
468          * By definition, 1KiB is 2 sectors.
469          */
470         back_max = bfqd->bfq_back_max * 2;
471 
472         /*
473          * Strict one way elevator _except_ in the case where we allow
474          * short backward seeks which are biased as twice the cost of a
475          * similar forward seek.
476          */
477         if (s1 >= last)
478                 d1 = s1 - last;
479         else if (s1 + back_max >= last)
480                 d1 = (last - s1) * bfqd->bfq_back_penalty;
481         else
482                 wrap |= BFQ_RQ1_WRAP;
483 
484         if (s2 >= last)
485                 d2 = s2 - last;
486         else if (s2 + back_max >= last)
487                 d2 = (last - s2) * bfqd->bfq_back_penalty;
488         else
489                 wrap |= BFQ_RQ2_WRAP;
490 
491         /* Found required data */
492 
493         /*
494          * By doing switch() on the bit mask "wrap" we avoid having to
495          * check two variables for all permutations: --> faster!
496          */
497         switch (wrap) {
498         case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
499                 if (d1 < d2)
500                         return rq1;
501                 else if (d2 < d1)
502                         return rq2;
503 
504                 if (s1 >= s2)
505                         return rq1;
506                 else
507                         return rq2;
508 
509         case BFQ_RQ2_WRAP:
510                 return rq1;
511         case BFQ_RQ1_WRAP:
512                 return rq2;
513         case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
514         default:
515                 /*
516                  * Since both rqs are wrapped,
517                  * start with the one that's further behind head
518                  * (--> only *one* back seek required),
519                  * since back seek takes more time than forward.
520                  */
521                 if (s1 <= s2)
522                         return rq1;
523                 else
524                         return rq2;
525         }
526 }
527 
528 /*
529  * Async I/O can easily starve sync I/O (both sync reads and sync
530  * writes), by consuming all tags. Similarly, storms of sync writes,
531  * such as those that sync(2) may trigger, can starve sync reads.
532  * Limit depths of async I/O and sync writes so as to counter both
533  * problems.
534  */
535 static void bfq_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
536 {
537         struct bfq_data *bfqd = data->q->elevator->elevator_data;
538 
539         if (op_is_sync(op) && !op_is_write(op))
540                 return;
541 
542         data->shallow_depth =
543                 bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op)];
544 
545         bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
546                         __func__, bfqd->wr_busy_queues, op_is_sync(op),
547                         data->shallow_depth);
548 }
549 
550 static struct bfq_queue *
551 bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
552                      sector_t sector, struct rb_node **ret_parent,
553                      struct rb_node ***rb_link)
554 {
555         struct rb_node **p, *parent;
556         struct bfq_queue *bfqq = NULL;
557 
558         parent = NULL;
559         p = &root->rb_node;
560         while (*p) {
561                 struct rb_node **n;
562 
563                 parent = *p;
564                 bfqq = rb_entry(parent, struct bfq_queue, pos_node);
565 
566                 /*
567                  * Sort strictly based on sector. Smallest to the left,
568                  * largest to the right.
569                  */
570                 if (sector > blk_rq_pos(bfqq->next_rq))
571                         n = &(*p)->rb_right;
572                 else if (sector < blk_rq_pos(bfqq->next_rq))
573                         n = &(*p)->rb_left;
574                 else
575                         break;
576                 p = n;
577                 bfqq = NULL;
578         }
579 
580         *ret_parent = parent;
581         if (rb_link)
582                 *rb_link = p;
583 
584         bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
585                 (unsigned long long)sector,
586                 bfqq ? bfqq->pid : 0);
587 
588         return bfqq;
589 }
590 
591 static bool bfq_too_late_for_merging(struct bfq_queue *bfqq)
592 {
593         return bfqq->service_from_backlogged > 0 &&
594                 time_is_before_jiffies(bfqq->first_IO_time +
595                                        bfq_merge_time_limit);
596 }
597 
598 /*
599  * The following function is not marked as __cold because it is
600  * actually cold, but for the same performance goal described in the
601  * comments on the likely() at the beginning of
602  * bfq_setup_cooperator(). Unexpectedly, to reach an even lower
603  * execution time for the case where this function is not invoked, we
604  * had to add an unlikely() in each involved if().
605  */
606 void __cold
607 bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
608 {
609         struct rb_node **p, *parent;
610         struct bfq_queue *__bfqq;
611 
612         if (bfqq->pos_root) {
613                 rb_erase(&bfqq->pos_node, bfqq->pos_root);
614                 bfqq->pos_root = NULL;
615         }
616 
617         /* oom_bfqq does not participate in queue merging */
618         if (bfqq == &bfqd->oom_bfqq)
619                 return;
620 
621         /*
622          * bfqq cannot be merged any longer (see comments in
623          * bfq_setup_cooperator): no point in adding bfqq into the
624          * position tree.
625          */
626         if (bfq_too_late_for_merging(bfqq))
627                 return;
628 
629         if (bfq_class_idle(bfqq))
630                 return;
631         if (!bfqq->next_rq)
632                 return;
633 
634         bfqq->pos_root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
635         __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root,
636                         blk_rq_pos(bfqq->next_rq), &parent, &p);
637         if (!__bfqq) {
638                 rb_link_node(&bfqq->pos_node, parent, p);
639                 rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
640         } else
641                 bfqq->pos_root = NULL;
642 }
643 
644 /*
645  * The following function returns false either if every active queue
646  * must receive the same share of the throughput (symmetric scenario),
647  * or, as a special case, if bfqq must receive a share of the
648  * throughput lower than or equal to the share that every other active
649  * queue must receive.  If bfqq does sync I/O, then these are the only
650  * two cases where bfqq happens to be guaranteed its share of the
651  * throughput even if I/O dispatching is not plugged when bfqq remains
652  * temporarily empty (for more details, see the comments in the
653  * function bfq_better_to_idle()). For this reason, the return value
654  * of this function is used to check whether I/O-dispatch plugging can
655  * be avoided.
656  *
657  * The above first case (symmetric scenario) occurs when:
658  * 1) all active queues have the same weight,
659  * 2) all active queues belong to the same I/O-priority class,
660  * 3) all active groups at the same level in the groups tree have the same
661  *    weight,
662  * 4) all active groups at the same level in the groups tree have the same
663  *    number of children.
664  *
665  * Unfortunately, keeping the necessary state for evaluating exactly
666  * the last two symmetry sub-conditions above would be quite complex
667  * and time consuming. Therefore this function evaluates, instead,
668  * only the following stronger three sub-conditions, for which it is
669  * much easier to maintain the needed state:
670  * 1) all active queues have the same weight,
671  * 2) all active queues belong to the same I/O-priority class,
672  * 3) there are no active groups.
673  * In particular, the last condition is always true if hierarchical
674  * support or the cgroups interface are not enabled, thus no state
675  * needs to be maintained in this case.
676  */
677 static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
678                                    struct bfq_queue *bfqq)
679 {
680         bool smallest_weight = bfqq &&
681                 bfqq->weight_counter &&
682                 bfqq->weight_counter ==
683                 container_of(
684                         rb_first_cached(&bfqd->queue_weights_tree),
685                         struct bfq_weight_counter,
686                         weights_node);
687 
688         /*
689          * For queue weights to differ, queue_weights_tree must contain
690          * at least two nodes.
691          */
692         bool varied_queue_weights = !smallest_weight &&
693                 !RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) &&
694                 (bfqd->queue_weights_tree.rb_root.rb_node->rb_left ||
695                  bfqd->queue_weights_tree.rb_root.rb_node->rb_right);
696 
697         bool multiple_classes_busy =
698                 (bfqd->busy_queues[0] && bfqd->busy_queues[1]) ||
699                 (bfqd->busy_queues[0] && bfqd->busy_queues[2]) ||
700                 (bfqd->busy_queues[1] && bfqd->busy_queues[2]);
701 
702         return varied_queue_weights || multiple_classes_busy
703 #ifdef CONFIG_BFQ_GROUP_IOSCHED
704                || bfqd->num_groups_with_pending_reqs > 0
705 #endif
706                 ;
707 }
708 
709 /*
710  * If the weight-counter tree passed as input contains no counter for
711  * the weight of the input queue, then add that counter; otherwise just
712  * increment the existing counter.
713  *
714  * Note that weight-counter trees contain few nodes in mostly symmetric
715  * scenarios. For example, if all queues have the same weight, then the
716  * weight-counter tree for the queues may contain at most one node.
717  * This holds even if low_latency is on, because weight-raised queues
718  * are not inserted in the tree.
719  * In most scenarios, the rate at which nodes are created/destroyed
720  * should be low too.
721  */
722 void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
723                           struct rb_root_cached *root)
724 {
725         struct bfq_entity *entity = &bfqq->entity;
726         struct rb_node **new = &(root->rb_root.rb_node), *parent = NULL;
727         bool leftmost = true;
728 
729         /*
730          * Do not insert if the queue is already associated with a
731          * counter, which happens if:
732          *   1) a request arrival has caused the queue to become both
733          *      non-weight-raised, and hence change its weight, and
734          *      backlogged; in this respect, each of the two events
735          *      causes an invocation of this function,
736          *   2) this is the invocation of this function caused by the
737          *      second event. This second invocation is actually useless,
738          *      and we handle this fact by exiting immediately. More
739          *      efficient or clearer solutions might possibly be adopted.
740          */
741         if (bfqq->weight_counter)
742                 return;
743 
744         while (*new) {
745                 struct bfq_weight_counter *__counter = container_of(*new,
746                                                 struct bfq_weight_counter,
747                                                 weights_node);
748                 parent = *new;
749 
750                 if (entity->weight == __counter->weight) {
751                         bfqq->weight_counter = __counter;
752                         goto inc_counter;
753                 }
754                 if (entity->weight < __counter->weight)
755                         new = &((*new)->rb_left);
756                 else {
757                         new = &((*new)->rb_right);
758                         leftmost = false;
759                 }
760         }
761 
762         bfqq->weight_counter = kzalloc(sizeof(struct bfq_weight_counter),
763                                        GFP_ATOMIC);
764 
765         /*
766          * In the unlucky event of an allocation failure, we just
767          * exit. This will cause the weight of queue to not be
768          * considered in bfq_asymmetric_scenario, which, in its turn,
769          * causes the scenario to be deemed wrongly symmetric in case
770          * bfqq's weight would have been the only weight making the
771          * scenario asymmetric.  On the bright side, no unbalance will
772          * however occur when bfqq becomes inactive again (the
773          * invocation of this function is triggered by an activation
774          * of queue).  In fact, bfq_weights_tree_remove does nothing
775          * if !bfqq->weight_counter.
776          */
777         if (unlikely(!bfqq->weight_counter))
778                 return;
779 
780         bfqq->weight_counter->weight = entity->weight;
781         rb_link_node(&bfqq->weight_counter->weights_node, parent, new);
782         rb_insert_color_cached(&bfqq->weight_counter->weights_node, root,
783                                 leftmost);
784 
785 inc_counter:
786         bfqq->weight_counter->num_active++;
787         bfqq->ref++;
788 }
789 
790 /*
791  * Decrement the weight counter associated with the queue, and, if the
792  * counter reaches 0, remove the counter from the tree.
793  * See the comments to the function bfq_weights_tree_add() for considerations
794  * about overhead.
795  */
796 void __bfq_weights_tree_remove(struct bfq_data *bfqd,
797                                struct bfq_queue *bfqq,
798                                struct rb_root_cached *root)
799 {
800         if (!bfqq->weight_counter)
801                 return;
802 
803         bfqq->weight_counter->num_active--;
804         if (bfqq->weight_counter->num_active > 0)
805                 goto reset_entity_pointer;
806 
807         rb_erase_cached(&bfqq->weight_counter->weights_node, root);
808         kfree(bfqq->weight_counter);
809 
810 reset_entity_pointer:
811         bfqq->weight_counter = NULL;
812         bfq_put_queue(bfqq);
813 }
814 
815 /*
816  * Invoke __bfq_weights_tree_remove on bfqq and decrement the number
817  * of active groups for each queue's inactive parent entity.
818  */
819 void bfq_weights_tree_remove(struct bfq_data *bfqd,
820                              struct bfq_queue *bfqq)
821 {
822         struct bfq_entity *entity = bfqq->entity.parent;
823 
824         for_each_entity(entity) {
825                 struct bfq_sched_data *sd = entity->my_sched_data;
826 
827                 if (sd->next_in_service || sd->in_service_entity) {
828                         /*
829                          * entity is still active, because either
830                          * next_in_service or in_service_entity is not
831                          * NULL (see the comments on the definition of
832                          * next_in_service for details on why
833                          * in_service_entity must be checked too).
834                          *
835                          * As a consequence, its parent entities are
836                          * active as well, and thus this loop must
837                          * stop here.
838                          */
839                         break;
840                 }
841 
842                 /*
843                  * The decrement of num_groups_with_pending_reqs is
844                  * not performed immediately upon the deactivation of
845                  * entity, but it is delayed to when it also happens
846                  * that the first leaf descendant bfqq of entity gets
847                  * all its pending requests completed. The following
848                  * instructions perform this delayed decrement, if
849                  * needed. See the comments on
850                  * num_groups_with_pending_reqs for details.
851                  */
852                 if (entity->in_groups_with_pending_reqs) {
853                         entity->in_groups_with_pending_reqs = false;
854                         bfqd->num_groups_with_pending_reqs--;
855                 }
856         }
857 
858         /*
859          * Next function is invoked last, because it causes bfqq to be
860          * freed if the following holds: bfqq is not in service and
861          * has no dispatched request. DO NOT use bfqq after the next
862          * function invocation.
863          */
864         __bfq_weights_tree_remove(bfqd, bfqq,
865                                   &bfqd->queue_weights_tree);
866 }
867 
868 /*
869  * Return expired entry, or NULL to just start from scratch in rbtree.
870  */
871 static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
872                                       struct request *last)
873 {
874         struct request *rq;
875 
876         if (bfq_bfqq_fifo_expire(bfqq))
877                 return NULL;
878 
879         bfq_mark_bfqq_fifo_expire(bfqq);
880 
881         rq = rq_entry_fifo(bfqq->fifo.next);
882 
883         if (rq == last || ktime_get_ns() < rq->fifo_time)
884                 return NULL;
885 
886         bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
887         return rq;
888 }
889 
890 static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
891                                         struct bfq_queue *bfqq,
892                                         struct request *last)
893 {
894         struct rb_node *rbnext = rb_next(&last->rb_node);
895         struct rb_node *rbprev = rb_prev(&last->rb_node);
896         struct request *next, *prev = NULL;
897 
898         /* Follow expired path, else get first next available. */
899         next = bfq_check_fifo(bfqq, last);
900         if (next)
901                 return next;
902 
903         if (rbprev)
904                 prev = rb_entry_rq(rbprev);
905 
906         if (rbnext)
907                 next = rb_entry_rq(rbnext);
908         else {
909                 rbnext = rb_first(&bfqq->sort_list);
910                 if (rbnext && rbnext != &last->rb_node)
911                         next = rb_entry_rq(rbnext);
912         }
913 
914         return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
915 }
916 
917 /* see the definition of bfq_async_charge_factor for details */
918 static unsigned long bfq_serv_to_charge(struct request *rq,
919                                         struct bfq_queue *bfqq)
920 {
921         if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1 ||
922             bfq_asymmetric_scenario(bfqq->bfqd, bfqq))
923                 return blk_rq_sectors(rq);
924 
925         return blk_rq_sectors(rq) * bfq_async_charge_factor;
926 }
927 
928 /**
929  * bfq_updated_next_req - update the queue after a new next_rq selection.
930  * @bfqd: the device data the queue belongs to.
931  * @bfqq: the queue to update.
932  *
933  * If the first request of a queue changes we make sure that the queue
934  * has enough budget to serve at least its first request (if the
935  * request has grown).  We do this because if the queue has not enough
936  * budget for its first request, it has to go through two dispatch
937  * rounds to actually get it dispatched.
938  */
939 static void bfq_updated_next_req(struct bfq_data *bfqd,
940                                  struct bfq_queue *bfqq)
941 {
942         struct bfq_entity *entity = &bfqq->entity;
943         struct request *next_rq = bfqq->next_rq;
944         unsigned long new_budget;
945 
946         if (!next_rq)
947                 return;
948 
949         if (bfqq == bfqd->in_service_queue)
950                 /*
951                  * In order not to break guarantees, budgets cannot be
952                  * changed after an entity has been selected.
953                  */
954                 return;
955 
956         new_budget = max_t(unsigned long,
957                            max_t(unsigned long, bfqq->max_budget,
958                                  bfq_serv_to_charge(next_rq, bfqq)),
959                            entity->service);
960         if (entity->budget != new_budget) {
961                 entity->budget = new_budget;
962                 bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
963                                          new_budget);
964                 bfq_requeue_bfqq(bfqd, bfqq, false);
965         }
966 }
967 
968 static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
969 {
970         u64 dur;
971 
972         if (bfqd->bfq_wr_max_time > 0)
973                 return bfqd->bfq_wr_max_time;
974 
975         dur = bfqd->rate_dur_prod;
976         do_div(dur, bfqd->peak_rate);
977 
978         /*
979          * Limit duration between 3 and 25 seconds. The upper limit
980          * has been conservatively set after the following worst case:
981          * on a QEMU/KVM virtual machine
982          * - running in a slow PC
983          * - with a virtual disk stacked on a slow low-end 5400rpm HDD
984          * - serving a heavy I/O workload, such as the sequential reading
985          *   of several files
986          * mplayer took 23 seconds to start, if constantly weight-raised.
987          *
988          * As for higher values than that accommodating the above bad
989          * scenario, tests show that higher values would often yield
990          * the opposite of the desired result, i.e., would worsen
991          * responsiveness by allowing non-interactive applications to
992          * preserve weight raising for too long.
993          *
994          * On the other end, lower values than 3 seconds make it
995          * difficult for most interactive tasks to complete their jobs
996          * before weight-raising finishes.
997          */
998         return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000));
999 }
1000 
1001 /* switch back from soft real-time to interactive weight raising */
1002 static void switch_back_to_interactive_wr(struct bfq_queue *bfqq,
1003                                           struct bfq_data *bfqd)
1004 {
1005         bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1006         bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1007         bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt;
1008 }
1009 
1010 static void
1011 bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
1012                       struct bfq_io_cq *bic, bool bfq_already_existing)
1013 {
1014         unsigned int old_wr_coeff = bfqq->wr_coeff;
1015         bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
1016 
1017         if (bic->saved_has_short_ttime)
1018                 bfq_mark_bfqq_has_short_ttime(bfqq);
1019         else
1020                 bfq_clear_bfqq_has_short_ttime(bfqq);
1021 
1022         if (bic->saved_IO_bound)
1023                 bfq_mark_bfqq_IO_bound(bfqq);
1024         else
1025                 bfq_clear_bfqq_IO_bound(bfqq);
1026 
1027         bfqq->entity.new_weight = bic->saved_weight;
1028         bfqq->ttime = bic->saved_ttime;
1029         bfqq->wr_coeff = bic->saved_wr_coeff;
1030         bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
1031         bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
1032         bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
1033 
1034         if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
1035             time_is_before_jiffies(bfqq->last_wr_start_finish +
1036                                    bfqq->wr_cur_max_time))) {
1037                 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
1038                     !bfq_bfqq_in_large_burst(bfqq) &&
1039                     time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt +
1040                                              bfq_wr_duration(bfqd))) {
1041                         switch_back_to_interactive_wr(bfqq, bfqd);
1042                 } else {
1043                         bfqq->wr_coeff = 1;
1044                         bfq_log_bfqq(bfqq->bfqd, bfqq,
1045                                      "resume state: switching off wr");
1046                 }
1047         }
1048 
1049         /* make sure weight will be updated, however we got here */
1050         bfqq->entity.prio_changed = 1;
1051 
1052         if (likely(!busy))
1053                 return;
1054 
1055         if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
1056                 bfqd->wr_busy_queues++;
1057         else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
1058                 bfqd->wr_busy_queues--;
1059 }
1060 
1061 static int bfqq_process_refs(struct bfq_queue *bfqq)
1062 {
1063         return bfqq->ref - bfqq->allocated - bfqq->entity.on_st_or_in_serv -
1064                 (bfqq->weight_counter != NULL);
1065 }
1066 
1067 /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
1068 static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1069 {
1070         struct bfq_queue *item;
1071         struct hlist_node *n;
1072 
1073         hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
1074                 hlist_del_init(&item->burst_list_node);
1075 
1076         /*
1077          * Start the creation of a new burst list only if there is no
1078          * active queue. See comments on the conditional invocation of
1079          * bfq_handle_burst().
1080          */
1081         if (bfq_tot_busy_queues(bfqd) == 0) {
1082                 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1083                 bfqd->burst_size = 1;
1084         } else
1085                 bfqd->burst_size = 0;
1086 
1087         bfqd->burst_parent_entity = bfqq->entity.parent;
1088 }
1089 
1090 /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
1091 static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1092 {
1093         /* Increment burst size to take into account also bfqq */
1094         bfqd->burst_size++;
1095 
1096         if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
1097                 struct bfq_queue *pos, *bfqq_item;
1098                 struct hlist_node *n;
1099 
1100                 /*
1101                  * Enough queues have been activated shortly after each
1102                  * other to consider this burst as large.
1103                  */
1104                 bfqd->large_burst = true;
1105 
1106                 /*
1107                  * We can now mark all queues in the burst list as
1108                  * belonging to a large burst.
1109                  */
1110                 hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
1111                                      burst_list_node)
1112                         bfq_mark_bfqq_in_large_burst(bfqq_item);
1113                 bfq_mark_bfqq_in_large_burst(bfqq);
1114 
1115                 /*
1116                  * From now on, and until the current burst finishes, any
1117                  * new queue being activated shortly after the last queue
1118                  * was inserted in the burst can be immediately marked as
1119                  * belonging to a large burst. So the burst list is not
1120                  * needed any more. Remove it.
1121                  */
1122                 hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
1123                                           burst_list_node)
1124                         hlist_del_init(&pos->burst_list_node);
1125         } else /*
1126                 * Burst not yet large: add bfqq to the burst list. Do
1127                 * not increment the ref counter for bfqq, because bfqq
1128                 * is removed from the burst list before freeing bfqq
1129                 * in put_queue.
1130                 */
1131                 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1132 }
1133 
1134 /*
1135  * If many queues belonging to the same group happen to be created
1136  * shortly after each other, then the processes associated with these
1137  * queues have typically a common goal. In particular, bursts of queue
1138  * creations are usually caused by services or applications that spawn
1139  * many parallel threads/processes. Examples are systemd during boot,
1140  * or git grep. To help these processes get their job done as soon as
1141  * possible, it is usually better to not grant either weight-raising
1142  * or device idling to their queues, unless these queues must be
1143  * protected from the I/O flowing through other active queues.
1144  *
1145  * In this comment we describe, firstly, the reasons why this fact
1146  * holds, and, secondly, the next function, which implements the main
1147  * steps needed to properly mark these queues so that they can then be
1148  * treated in a different way.
1149  *
1150  * The above services or applications benefit mostly from a high
1151  * throughput: the quicker the requests of the activated queues are
1152  * cumulatively served, the sooner the target job of these queues gets
1153  * completed. As a consequence, weight-raising any of these queues,
1154  * which also implies idling the device for it, is almost always
1155  * counterproductive, unless there are other active queues to isolate
1156  * these new queues from. If there no other active queues, then
1157  * weight-raising these new queues just lowers throughput in most
1158  * cases.
1159  *
1160  * On the other hand, a burst of queue creations may be caused also by
1161  * the start of an application that does not consist of a lot of
1162  * parallel I/O-bound threads. In fact, with a complex application,
1163  * several short processes may need to be executed to start-up the
1164  * application. In this respect, to start an application as quickly as
1165  * possible, the best thing to do is in any case to privilege the I/O
1166  * related to the application with respect to all other
1167  * I/O. Therefore, the best strategy to start as quickly as possible
1168  * an application that causes a burst of queue creations is to
1169  * weight-raise all the queues created during the burst. This is the
1170  * exact opposite of the best strategy for the other type of bursts.
1171  *
1172  * In the end, to take the best action for each of the two cases, the
1173  * two types of bursts need to be distinguished. Fortunately, this
1174  * seems relatively easy, by looking at the sizes of the bursts. In
1175  * particular, we found a threshold such that only bursts with a
1176  * larger size than that threshold are apparently caused by
1177  * services or commands such as systemd or git grep. For brevity,
1178  * hereafter we call just 'large' these bursts. BFQ *does not*
1179  * weight-raise queues whose creation occurs in a large burst. In
1180  * addition, for each of these queues BFQ performs or does not perform
1181  * idling depending on which choice boosts the throughput more. The
1182  * exact choice depends on the device and request pattern at
1183  * hand.
1184  *
1185  * Unfortunately, false positives may occur while an interactive task
1186  * is starting (e.g., an application is being started). The
1187  * consequence is that the queues associated with the task do not
1188  * enjoy weight raising as expected. Fortunately these false positives
1189  * are very rare. They typically occur if some service happens to
1190  * start doing I/O exactly when the interactive task starts.
1191  *
1192  * Turning back to the next function, it is invoked only if there are
1193  * no active queues (apart from active queues that would belong to the
1194  * same, possible burst bfqq would belong to), and it implements all
1195  * the steps needed to detect the occurrence of a large burst and to
1196  * properly mark all the queues belonging to it (so that they can then
1197  * be treated in a different way). This goal is achieved by
1198  * maintaining a "burst list" that holds, temporarily, the queues that
1199  * belong to the burst in progress. The list is then used to mark
1200  * these queues as belonging to a large burst if the burst does become
1201  * large. The main steps are the following.
1202  *
1203  * . when the very first queue is created, the queue is inserted into the
1204  *   list (as it could be the first queue in a possible burst)
1205  *
1206  * . if the current burst has not yet become large, and a queue Q that does
1207  *   not yet belong to the burst is activated shortly after the last time
1208  *   at which a new queue entered the burst list, then the function appends
1209  *   Q to the burst list
1210  *
1211  * . if, as a consequence of the previous step, the burst size reaches
1212  *   the large-burst threshold, then
1213  *
1214  *     . all the queues in the burst list are marked as belonging to a
1215  *       large burst
1216  *
1217  *     . the burst list is deleted; in fact, the burst list already served
1218  *       its purpose (keeping temporarily track of the queues in a burst,
1219  *       so as to be able to mark them as belonging to a large burst in the
1220  *       previous sub-step), and now is not needed any more
1221  *
1222  *     . the device enters a large-burst mode
1223  *
1224  * . if a queue Q that does not belong to the burst is created while
1225  *   the device is in large-burst mode and shortly after the last time
1226  *   at which a queue either entered the burst list or was marked as
1227  *   belonging to the current large burst, then Q is immediately marked
1228  *   as belonging to a large burst.
1229  *
1230  * . if a queue Q that does not belong to the burst is created a while
1231  *   later, i.e., not shortly after, than the last time at which a queue
1232  *   either entered the burst list or was marked as belonging to the
1233  *   current large burst, then the current burst is deemed as finished and:
1234  *
1235  *        . the large-burst mode is reset if set
1236  *
1237  *        . the burst list is emptied
1238  *
1239  *        . Q is inserted in the burst list, as Q may be the first queue
1240  *          in a possible new burst (then the burst list contains just Q
1241  *          after this step).
1242  */
1243 static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1244 {
1245         /*
1246          * If bfqq is already in the burst list or is part of a large
1247          * burst, or finally has just been split, then there is
1248          * nothing else to do.
1249          */
1250         if (!hlist_unhashed(&bfqq->burst_list_node) ||
1251             bfq_bfqq_in_large_burst(bfqq) ||
1252             time_is_after_eq_jiffies(bfqq->split_time +
1253                                      msecs_to_jiffies(10)))
1254                 return;
1255 
1256         /*
1257          * If bfqq's creation happens late enough, or bfqq belongs to
1258          * a different group than the burst group, then the current
1259          * burst is finished, and related data structures must be
1260          * reset.
1261          *
1262          * In this respect, consider the special case where bfqq is
1263          * the very first queue created after BFQ is selected for this
1264          * device. In this case, last_ins_in_burst and
1265          * burst_parent_entity are not yet significant when we get
1266          * here. But it is easy to verify that, whether or not the
1267          * following condition is true, bfqq will end up being
1268          * inserted into the burst list. In particular the list will
1269          * happen to contain only bfqq. And this is exactly what has
1270          * to happen, as bfqq may be the first queue of the first
1271          * burst.
1272          */
1273         if (time_is_before_jiffies(bfqd->last_ins_in_burst +
1274             bfqd->bfq_burst_interval) ||
1275             bfqq->entity.parent != bfqd->burst_parent_entity) {
1276                 bfqd->large_burst = false;
1277                 bfq_reset_burst_list(bfqd, bfqq);
1278                 goto end;
1279         }
1280 
1281         /*
1282          * If we get here, then bfqq is being activated shortly after the
1283          * last queue. So, if the current burst is also large, we can mark
1284          * bfqq as belonging to this large burst immediately.
1285          */
1286         if (bfqd->large_burst) {
1287                 bfq_mark_bfqq_in_large_burst(bfqq);
1288                 goto end;
1289         }
1290 
1291         /*
1292          * If we get here, then a large-burst state has not yet been
1293          * reached, but bfqq is being activated shortly after the last
1294          * queue. Then we add bfqq to the burst.
1295          */
1296         bfq_add_to_burst(bfqd, bfqq);
1297 end:
1298         /*
1299          * At this point, bfqq either has been added to the current
1300          * burst or has caused the current burst to terminate and a
1301          * possible new burst to start. In particular, in the second
1302          * case, bfqq has become the first queue in the possible new
1303          * burst.  In both cases last_ins_in_burst needs to be moved
1304          * forward.
1305          */
1306         bfqd->last_ins_in_burst = jiffies;
1307 }
1308 
1309 static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
1310 {
1311         struct bfq_entity *entity = &bfqq->entity;
1312 
1313         return entity->budget - entity->service;
1314 }
1315 
1316 /*
1317  * If enough samples have been computed, return the current max budget
1318  * stored in bfqd, which is dynamically updated according to the
1319  * estimated disk peak rate; otherwise return the default max budget
1320  */
1321 static int bfq_max_budget(struct bfq_data *bfqd)
1322 {
1323         if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1324                 return bfq_default_max_budget;
1325         else
1326                 return bfqd->bfq_max_budget;
1327 }
1328 
1329 /*
1330  * Return min budget, which is a fraction of the current or default
1331  * max budget (trying with 1/32)
1332  */
1333 static int bfq_min_budget(struct bfq_data *bfqd)
1334 {
1335         if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1336                 return bfq_default_max_budget / 32;
1337         else
1338                 return bfqd->bfq_max_budget / 32;
1339 }
1340 
1341 /*
1342  * The next function, invoked after the input queue bfqq switches from
1343  * idle to busy, updates the budget of bfqq. The function also tells
1344  * whether the in-service queue should be expired, by returning
1345  * true. The purpose of expiring the in-service queue is to give bfqq
1346  * the chance to possibly preempt the in-service queue, and the reason
1347  * for preempting the in-service queue is to achieve one of the two
1348  * goals below.
1349  *
1350  * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1351  * expired because it has remained idle. In particular, bfqq may have
1352  * expired for one of the following two reasons:
1353  *
1354  * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1355  *   and did not make it to issue a new request before its last
1356  *   request was served;
1357  *
1358  * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1359  *   a new request before the expiration of the idling-time.
1360  *
1361  * Even if bfqq has expired for one of the above reasons, the process
1362  * associated with the queue may be however issuing requests greedily,
1363  * and thus be sensitive to the bandwidth it receives (bfqq may have
1364  * remained idle for other reasons: CPU high load, bfqq not enjoying
1365  * idling, I/O throttling somewhere in the path from the process to
1366  * the I/O scheduler, ...). But if, after every expiration for one of
1367  * the above two reasons, bfqq has to wait for the service of at least
1368  * one full budget of another queue before being served again, then
1369  * bfqq is likely to get a much lower bandwidth or resource time than
1370  * its reserved ones. To address this issue, two countermeasures need
1371  * to be taken.
1372  *
1373  * First, the budget and the timestamps of bfqq need to be updated in
1374  * a special way on bfqq reactivation: they need to be updated as if
1375  * bfqq did not remain idle and did not expire. In fact, if they are
1376  * computed as if bfqq expired and remained idle until reactivation,
1377  * then the process associated with bfqq is treated as if, instead of
1378  * being greedy, it stopped issuing requests when bfqq remained idle,
1379  * and restarts issuing requests only on this reactivation. In other
1380  * words, the scheduler does not help the process recover the "service
1381  * hole" between bfqq expiration and reactivation. As a consequence,
1382  * the process receives a lower bandwidth than its reserved one. In
1383  * contrast, to recover this hole, the budget must be updated as if
1384  * bfqq was not expired at all before this reactivation, i.e., it must
1385  * be set to the value of the remaining budget when bfqq was
1386  * expired. Along the same line, timestamps need to be assigned the
1387  * value they had the last time bfqq was selected for service, i.e.,
1388  * before last expiration. Thus timestamps need to be back-shifted
1389  * with respect to their normal computation (see [1] for more details
1390  * on this tricky aspect).
1391  *
1392  * Secondly, to allow the process to recover the hole, the in-service
1393  * queue must be expired too, to give bfqq the chance to preempt it
1394  * immediately. In fact, if bfqq has to wait for a full budget of the
1395  * in-service queue to be completed, then it may become impossible to
1396  * let the process recover the hole, even if the back-shifted
1397  * timestamps of bfqq are lower than those of the in-service queue. If
1398  * this happens for most or all of the holes, then the process may not
1399  * receive its reserved bandwidth. In this respect, it is worth noting
1400  * that, being the service of outstanding requests unpreemptible, a
1401  * little fraction of the holes may however be unrecoverable, thereby
1402  * causing a little loss of bandwidth.
1403  *
1404  * The last important point is detecting whether bfqq does need this
1405  * bandwidth recovery. In this respect, the next function deems the
1406  * process associated with bfqq greedy, and thus allows it to recover
1407  * the hole, if: 1) the process is waiting for the arrival of a new
1408  * request (which implies that bfqq expired for one of the above two
1409  * reasons), and 2) such a request has arrived soon. The first
1410  * condition is controlled through the flag non_blocking_wait_rq,
1411  * while the second through the flag arrived_in_time. If both
1412  * conditions hold, then the function computes the budget in the
1413  * above-described special way, and signals that the in-service queue
1414  * should be expired. Timestamp back-shifting is done later in
1415  * __bfq_activate_entity.
1416  *
1417  * 2. Reduce latency. Even if timestamps are not backshifted to let
1418  * the process associated with bfqq recover a service hole, bfqq may
1419  * however happen to have, after being (re)activated, a lower finish
1420  * timestamp than the in-service queue.  That is, the next budget of
1421  * bfqq may have to be completed before the one of the in-service
1422  * queue. If this is the case, then preempting the in-service queue
1423  * allows this goal to be achieved, apart from the unpreemptible,
1424  * outstanding requests mentioned above.
1425  *
1426  * Unfortunately, regardless of which of the above two goals one wants
1427  * to achieve, service trees need first to be updated to know whether
1428  * the in-service queue must be preempted. To have service trees
1429  * correctly updated, the in-service queue must be expired and
1430  * rescheduled, and bfqq must be scheduled too. This is one of the
1431  * most costly operations (in future versions, the scheduling
1432  * mechanism may be re-designed in such a way to make it possible to
1433  * know whether preemption is needed without needing to update service
1434  * trees). In addition, queue preemptions almost always cause random
1435  * I/O, which may in turn cause loss of throughput. Finally, there may
1436  * even be no in-service queue when the next function is invoked (so,
1437  * no queue to compare timestamps with). Because of these facts, the
1438  * next function adopts the following simple scheme to avoid costly
1439  * operations, too frequent preemptions and too many dependencies on
1440  * the state of the scheduler: it requests the expiration of the
1441  * in-service queue (unconditionally) only for queues that need to
1442  * recover a hole. Then it delegates to other parts of the code the
1443  * responsibility of handling the above case 2.
1444  */
1445 static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
1446                                                 struct bfq_queue *bfqq,
1447                                                 bool arrived_in_time)
1448 {
1449         struct bfq_entity *entity = &bfqq->entity;
1450 
1451         /*
1452          * In the next compound condition, we check also whether there
1453          * is some budget left, because otherwise there is no point in
1454          * trying to go on serving bfqq with this same budget: bfqq
1455          * would be expired immediately after being selected for
1456          * service. This would only cause useless overhead.
1457          */
1458         if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time &&
1459             bfq_bfqq_budget_left(bfqq) > 0) {
1460                 /*
1461                  * We do not clear the flag non_blocking_wait_rq here, as
1462                  * the latter is used in bfq_activate_bfqq to signal
1463                  * that timestamps need to be back-shifted (and is
1464                  * cleared right after).
1465                  */
1466 
1467                 /*
1468                  * In next assignment we rely on that either
1469                  * entity->service or entity->budget are not updated
1470                  * on expiration if bfqq is empty (see
1471                  * __bfq_bfqq_recalc_budget). Thus both quantities
1472                  * remain unchanged after such an expiration, and the
1473                  * following statement therefore assigns to
1474                  * entity->budget the remaining budget on such an
1475                  * expiration.
1476                  */
1477                 entity->budget = min_t(unsigned long,
1478                                        bfq_bfqq_budget_left(bfqq),
1479                                        bfqq->max_budget);
1480 
1481                 /*
1482                  * At this point, we have used entity->service to get
1483                  * the budget left (needed for updating
1484                  * entity->budget). Thus we finally can, and have to,
1485                  * reset entity->service. The latter must be reset
1486                  * because bfqq would otherwise be charged again for
1487                  * the service it has received during its previous
1488                  * service slot(s).
1489                  */
1490                 entity->service = 0;
1491 
1492                 return true;
1493         }
1494 
1495         /*
1496          * We can finally complete expiration, by setting service to 0.
1497          */
1498         entity->service = 0;
1499         entity->budget = max_t(unsigned long, bfqq->max_budget,
1500                                bfq_serv_to_charge(bfqq->next_rq, bfqq));
1501         bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1502         return false;
1503 }
1504 
1505 /*
1506  * Return the farthest past time instant according to jiffies
1507  * macros.
1508  */
1509 static unsigned long bfq_smallest_from_now(void)
1510 {
1511         return jiffies - MAX_JIFFY_OFFSET;
1512 }
1513 
1514 static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
1515                                              struct bfq_queue *bfqq,
1516                                              unsigned int old_wr_coeff,
1517                                              bool wr_or_deserves_wr,
1518                                              bool interactive,
1519                                              bool in_burst,
1520                                              bool soft_rt)
1521 {
1522         if (old_wr_coeff == 1 && wr_or_deserves_wr) {
1523                 /* start a weight-raising period */
1524                 if (interactive) {
1525                         bfqq->service_from_wr = 0;
1526                         bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1527                         bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1528                 } else {
1529                         /*
1530                          * No interactive weight raising in progress
1531                          * here: assign minus infinity to
1532                          * wr_start_at_switch_to_srt, to make sure
1533                          * that, at the end of the soft-real-time
1534                          * weight raising periods that is starting
1535                          * now, no interactive weight-raising period
1536                          * may be wrongly considered as still in
1537                          * progress (and thus actually started by
1538                          * mistake).
1539                          */
1540                         bfqq->wr_start_at_switch_to_srt =
1541                                 bfq_smallest_from_now();
1542                         bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1543                                 BFQ_SOFTRT_WEIGHT_FACTOR;
1544                         bfqq->wr_cur_max_time =
1545                                 bfqd->bfq_wr_rt_max_time;
1546                 }
1547 
1548                 /*
1549                  * If needed, further reduce budget to make sure it is
1550                  * close to bfqq's backlog, so as to reduce the
1551                  * scheduling-error component due to a too large
1552                  * budget. Do not care about throughput consequences,
1553                  * but only about latency. Finally, do not assign a
1554                  * too small budget either, to avoid increasing
1555                  * latency by causing too frequent expirations.
1556                  */
1557                 bfqq->entity.budget = min_t(unsigned long,
1558                                             bfqq->entity.budget,
1559                                             2 * bfq_min_budget(bfqd));
1560         } else if (old_wr_coeff > 1) {
1561                 if (interactive) { /* update wr coeff and duration */
1562                         bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1563                         bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1564                 } else if (in_burst)
1565                         bfqq->wr_coeff = 1;
1566                 else if (soft_rt) {
1567                         /*
1568                          * The application is now or still meeting the
1569                          * requirements for being deemed soft rt.  We
1570                          * can then correctly and safely (re)charge
1571                          * the weight-raising duration for the
1572                          * application with the weight-raising
1573                          * duration for soft rt applications.
1574                          *
1575                          * In particular, doing this recharge now, i.e.,
1576                          * before the weight-raising period for the
1577                          * application finishes, reduces the probability
1578                          * of the following negative scenario:
1579                          * 1) the weight of a soft rt application is
1580                          *    raised at startup (as for any newly
1581                          *    created application),
1582                          * 2) since the application is not interactive,
1583                          *    at a certain time weight-raising is
1584                          *    stopped for the application,
1585                          * 3) at that time the application happens to
1586                          *    still have pending requests, and hence
1587                          *    is destined to not have a chance to be
1588                          *    deemed soft rt before these requests are
1589                          *    completed (see the comments to the
1590                          *    function bfq_bfqq_softrt_next_start()
1591                          *    for details on soft rt detection),
1592                          * 4) these pending requests experience a high
1593                          *    latency because the application is not
1594                          *    weight-raised while they are pending.
1595                          */
1596                         if (bfqq->wr_cur_max_time !=
1597                                 bfqd->bfq_wr_rt_max_time) {
1598                                 bfqq->wr_start_at_switch_to_srt =
1599                                         bfqq->last_wr_start_finish;
1600 
1601                                 bfqq->wr_cur_max_time =
1602                                         bfqd->bfq_wr_rt_max_time;
1603                                 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1604                                         BFQ_SOFTRT_WEIGHT_FACTOR;
1605                         }
1606                         bfqq->last_wr_start_finish = jiffies;
1607                 }
1608         }
1609 }
1610 
1611 static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
1612                                         struct bfq_queue *bfqq)
1613 {
1614         return bfqq->dispatched == 0 &&
1615                 time_is_before_jiffies(
1616                         bfqq->budget_timeout +
1617                         bfqd->bfq_wr_min_idle_time);
1618 }
1619 
1620 
1621 /*
1622  * Return true if bfqq is in a higher priority class, or has a higher
1623  * weight than the in-service queue.
1624  */
1625 static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
1626                                             struct bfq_queue *in_serv_bfqq)
1627 {
1628         int bfqq_weight, in_serv_weight;
1629 
1630         if (bfqq->ioprio_class < in_serv_bfqq->ioprio_class)
1631                 return true;
1632 
1633         if (in_serv_bfqq->entity.parent == bfqq->entity.parent) {
1634                 bfqq_weight = bfqq->entity.weight;
1635                 in_serv_weight = in_serv_bfqq->entity.weight;
1636         } else {
1637                 if (bfqq->entity.parent)
1638                         bfqq_weight = bfqq->entity.parent->weight;
1639                 else
1640                         bfqq_weight = bfqq->entity.weight;
1641                 if (in_serv_bfqq->entity.parent)
1642                         in_serv_weight = in_serv_bfqq->entity.parent->weight;
1643                 else
1644                         in_serv_weight = in_serv_bfqq->entity.weight;
1645         }
1646 
1647         return bfqq_weight > in_serv_weight;
1648 }
1649 
1650 static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
1651                                              struct bfq_queue *bfqq,
1652                                              int old_wr_coeff,
1653                                              struct request *rq,
1654                                              bool *interactive)
1655 {
1656         bool soft_rt, in_burst, wr_or_deserves_wr,
1657                 bfqq_wants_to_preempt,
1658                 idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
1659                 /*
1660                  * See the comments on
1661                  * bfq_bfqq_update_budg_for_activation for
1662                  * details on the usage of the next variable.
1663                  */
1664                 arrived_in_time =  ktime_get_ns() <=
1665                         bfqq->ttime.last_end_request +
1666                         bfqd->bfq_slice_idle * 3;
1667 
1668 
1669         /*
1670          * bfqq deserves to be weight-raised if:
1671          * - it is sync,
1672          * - it does not belong to a large burst,
1673          * - it has been idle for enough time or is soft real-time,
1674          * - is linked to a bfq_io_cq (it is not shared in any sense).
1675          */
1676         in_burst = bfq_bfqq_in_large_burst(bfqq);
1677         soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
1678                 !BFQQ_TOTALLY_SEEKY(bfqq) &&
1679                 !in_burst &&
1680                 time_is_before_jiffies(bfqq->soft_rt_next_start) &&
1681                 bfqq->dispatched == 0;
1682         *interactive = !in_burst && idle_for_long_time;
1683         wr_or_deserves_wr = bfqd->low_latency &&
1684                 (bfqq->wr_coeff > 1 ||
1685                  (bfq_bfqq_sync(bfqq) &&
1686                   bfqq->bic && (*interactive || soft_rt)));
1687 
1688         /*
1689          * Using the last flag, update budget and check whether bfqq
1690          * may want to preempt the in-service queue.
1691          */
1692         bfqq_wants_to_preempt =
1693                 bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
1694                                                     arrived_in_time);
1695 
1696         /*
1697          * If bfqq happened to be activated in a burst, but has been
1698          * idle for much more than an interactive queue, then we
1699          * assume that, in the overall I/O initiated in the burst, the
1700          * I/O associated with bfqq is finished. So bfqq does not need
1701          * to be treated as a queue belonging to a burst
1702          * anymore. Accordingly, we reset bfqq's in_large_burst flag
1703          * if set, and remove bfqq from the burst list if it's
1704          * there. We do not decrement burst_size, because the fact
1705          * that bfqq does not need to belong to the burst list any
1706          * more does not invalidate the fact that bfqq was created in
1707          * a burst.
1708          */
1709         if (likely(!bfq_bfqq_just_created(bfqq)) &&
1710             idle_for_long_time &&
1711             time_is_before_jiffies(
1712                     bfqq->budget_timeout +
1713                     msecs_to_jiffies(10000))) {
1714                 hlist_del_init(&bfqq->burst_list_node);
1715                 bfq_clear_bfqq_in_large_burst(bfqq);
1716         }
1717 
1718         bfq_clear_bfqq_just_created(bfqq);
1719 
1720 
1721         if (!bfq_bfqq_IO_bound(bfqq)) {
1722                 if (arrived_in_time) {
1723                         bfqq->requests_within_timer++;
1724                         if (bfqq->requests_within_timer >=
1725                             bfqd->bfq_requests_within_timer)
1726                                 bfq_mark_bfqq_IO_bound(bfqq);
1727                 } else
1728                         bfqq->requests_within_timer = 0;
1729         }
1730 
1731         if (bfqd->low_latency) {
1732                 if (unlikely(time_is_after_jiffies(bfqq->split_time)))
1733                         /* wraparound */
1734                         bfqq->split_time =
1735                                 jiffies - bfqd->bfq_wr_min_idle_time - 1;
1736 
1737                 if (time_is_before_jiffies(bfqq->split_time +
1738                                            bfqd->bfq_wr_min_idle_time)) {
1739                         bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
1740                                                          old_wr_coeff,
1741                                                          wr_or_deserves_wr,
1742                                                          *interactive,
1743                                                          in_burst,
1744                                                          soft_rt);
1745 
1746                         if (old_wr_coeff != bfqq->wr_coeff)
1747                                 bfqq->entity.prio_changed = 1;
1748                 }
1749         }
1750 
1751         bfqq->last_idle_bklogged = jiffies;
1752         bfqq->service_from_backlogged = 0;
1753         bfq_clear_bfqq_softrt_update(bfqq);
1754 
1755         bfq_add_bfqq_busy(bfqd, bfqq);
1756 
1757         /*
1758          * Expire in-service queue only if preemption may be needed
1759          * for guarantees. In particular, we care only about two
1760          * cases. The first is that bfqq has to recover a service
1761          * hole, as explained in the comments on
1762          * bfq_bfqq_update_budg_for_activation(), i.e., that
1763          * bfqq_wants_to_preempt is true. However, if bfqq does not
1764          * carry time-critical I/O, then bfqq's bandwidth is less
1765          * important than that of queues that carry time-critical I/O.
1766          * So, as a further constraint, we consider this case only if
1767          * bfqq is at least as weight-raised, i.e., at least as time
1768          * critical, as the in-service queue.
1769          *
1770          * The second case is that bfqq is in a higher priority class,
1771          * or has a higher weight than the in-service queue. If this
1772          * condition does not hold, we don't care because, even if
1773          * bfqq does not start to be served immediately, the resulting
1774          * delay for bfqq's I/O is however lower or much lower than
1775          * the ideal completion time to be guaranteed to bfqq's I/O.
1776          *
1777          * In both cases, preemption is needed only if, according to
1778          * the timestamps of both bfqq and of the in-service queue,
1779          * bfqq actually is the next queue to serve. So, to reduce
1780          * useless preemptions, the return value of
1781          * next_queue_may_preempt() is considered in the next compound
1782          * condition too. Yet next_queue_may_preempt() just checks a
1783          * simple, necessary condition for bfqq to be the next queue
1784          * to serve. In fact, to evaluate a sufficient condition, the
1785          * timestamps of the in-service queue would need to be
1786          * updated, and this operation is quite costly (see the
1787          * comments on bfq_bfqq_update_budg_for_activation()).
1788          */
1789         if (bfqd->in_service_queue &&
1790             ((bfqq_wants_to_preempt &&
1791               bfqq->wr_coeff >= bfqd->in_service_queue->wr_coeff) ||
1792              bfq_bfqq_higher_class_or_weight(bfqq, bfqd->in_service_queue)) &&
1793             next_queue_may_preempt(bfqd))
1794                 bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
1795                                 false, BFQQE_PREEMPTED);
1796 }
1797 
1798 static void bfq_reset_inject_limit(struct bfq_data *bfqd,
1799                                    struct bfq_queue *bfqq)
1800 {
1801         /* invalidate baseline total service time */
1802         bfqq->last_serv_time_ns = 0;
1803 
1804         /*
1805          * Reset pointer in case we are waiting for
1806          * some request completion.
1807          */
1808         bfqd->waited_rq = NULL;
1809 
1810         /*
1811          * If bfqq has a short think time, then start by setting the
1812          * inject limit to 0 prudentially, because the service time of
1813          * an injected I/O request may be higher than the think time
1814          * of bfqq, and therefore, if one request was injected when
1815          * bfqq remains empty, this injected request might delay the
1816          * service of the next I/O request for bfqq significantly. In
1817          * case bfqq can actually tolerate some injection, then the
1818          * adaptive update will however raise the limit soon. This
1819          * lucky circumstance holds exactly because bfqq has a short
1820          * think time, and thus, after remaining empty, is likely to
1821          * get new I/O enqueued---and then completed---before being
1822          * expired. This is the very pattern that gives the
1823          * limit-update algorithm the chance to measure the effect of
1824          * injection on request service times, and then to update the
1825          * limit accordingly.
1826          *
1827          * However, in the following special case, the inject limit is
1828          * left to 1 even if the think time is short: bfqq's I/O is
1829          * synchronized with that of some other queue, i.e., bfqq may
1830          * receive new I/O only after the I/O of the other queue is
1831          * completed. Keeping the inject limit to 1 allows the
1832          * blocking I/O to be served while bfqq is in service. And
1833          * this is very convenient both for bfqq and for overall
1834          * throughput, as explained in detail in the comments in
1835          * bfq_update_has_short_ttime().
1836          *
1837          * On the opposite end, if bfqq has a long think time, then
1838          * start directly by 1, because:
1839          * a) on the bright side, keeping at most one request in
1840          * service in the drive is unlikely to cause any harm to the
1841          * latency of bfqq's requests, as the service time of a single
1842          * request is likely to be lower than the think time of bfqq;
1843          * b) on the downside, after becoming empty, bfqq is likely to
1844          * expire before getting its next request. With this request
1845          * arrival pattern, it is very hard to sample total service
1846          * times and update the inject limit accordingly (see comments
1847          * on bfq_update_inject_limit()). So the limit is likely to be
1848          * never, or at least seldom, updated.  As a consequence, by
1849          * setting the limit to 1, we avoid that no injection ever
1850          * occurs with bfqq. On the downside, this proactive step
1851          * further reduces chances to actually compute the baseline
1852          * total service time. Thus it reduces chances to execute the
1853          * limit-update algorithm and possibly raise the limit to more
1854          * than 1.
1855          */
1856         if (bfq_bfqq_has_short_ttime(bfqq))
1857                 bfqq->inject_limit = 0;
1858         else
1859                 bfqq->inject_limit = 1;
1860 
1861         bfqq->decrease_time_jif = jiffies;
1862 }
1863 
1864 static void bfq_add_request(struct request *rq)
1865 {
1866         struct bfq_queue *bfqq = RQ_BFQQ(rq);
1867         struct bfq_data *bfqd = bfqq->bfqd;
1868         struct request *next_rq, *prev;
1869         unsigned int old_wr_coeff = bfqq->wr_coeff;
1870         bool interactive = false;
1871 
1872         bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
1873         bfqq->queued[rq_is_sync(rq)]++;
1874         bfqd->queued++;
1875 
1876         if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_sync(bfqq)) {
1877                 /*
1878                  * Detect whether bfqq's I/O seems synchronized with
1879                  * that of some other queue, i.e., whether bfqq, after
1880                  * remaining empty, happens to receive new I/O only
1881                  * right after some I/O request of the other queue has
1882                  * been completed. We call waker queue the other
1883                  * queue, and we assume, for simplicity, that bfqq may
1884                  * have at most one waker queue.
1885                  *
1886                  * A remarkable throughput boost can be reached by
1887                  * unconditionally injecting the I/O of the waker
1888                  * queue, every time a new bfq_dispatch_request
1889                  * happens to be invoked while I/O is being plugged
1890                  * for bfqq.  In addition to boosting throughput, this
1891                  * unblocks bfqq's I/O, thereby improving bandwidth
1892                  * and latency for bfqq. Note that these same results
1893                  * may be achieved with the general injection
1894                  * mechanism, but less effectively. For details on
1895                  * this aspect, see the comments on the choice of the
1896                  * queue for injection in bfq_select_queue().
1897                  *
1898                  * Turning back to the detection of a waker queue, a
1899                  * queue Q is deemed as a waker queue for bfqq if, for
1900                  * two consecutive times, bfqq happens to become non
1901                  * empty right after a request of Q has been
1902                  * completed. In particular, on the first time, Q is
1903                  * tentatively set as a candidate waker queue, while
1904                  * on the second time, the flag
1905                  * bfq_bfqq_has_waker(bfqq) is set to confirm that Q
1906                  * is a waker queue for bfqq. These detection steps
1907                  * are performed only if bfqq has a long think time,
1908                  * so as to make it more likely that bfqq's I/O is
1909                  * actually being blocked by a synchronization. This
1910                  * last filter, plus the above two-times requirement,
1911                  * make false positives less likely.
1912                  *
1913                  * NOTE
1914                  *
1915                  * The sooner a waker queue is detected, the sooner
1916                  * throughput can be boosted by injecting I/O from the
1917                  * waker queue. Fortunately, detection is likely to be
1918                  * actually fast, for the following reasons. While
1919                  * blocked by synchronization, bfqq has a long think
1920                  * time. This implies that bfqq's inject limit is at
1921                  * least equal to 1 (see the comments in
1922                  * bfq_update_inject_limit()). So, thanks to
1923                  * injection, the waker queue is likely to be served
1924                  * during the very first I/O-plugging time interval
1925                  * for bfqq. This triggers the first step of the
1926                  * detection mechanism. Thanks again to injection, the
1927                  * candidate waker queue is then likely to be
1928                  * confirmed no later than during the next
1929                  * I/O-plugging interval for bfqq.
1930                  */
1931                 if (bfqd->last_completed_rq_bfqq &&
1932                     !bfq_bfqq_has_short_ttime(bfqq) &&
1933                     ktime_get_ns() - bfqd->last_completion <
1934                     200 * NSEC_PER_USEC) {
1935                         if (bfqd->last_completed_rq_bfqq != bfqq &&
1936                             bfqd->last_completed_rq_bfqq !=
1937                             bfqq->waker_bfqq) {
1938                                 /*
1939                                  * First synchronization detected with
1940                                  * a candidate waker queue, or with a
1941                                  * different candidate waker queue
1942                                  * from the current one.
1943                                  */
1944                                 bfqq->waker_bfqq = bfqd->last_completed_rq_bfqq;
1945 
1946                                 /*
1947                                  * If the waker queue disappears, then
1948                                  * bfqq->waker_bfqq must be reset. To
1949                                  * this goal, we maintain in each
1950                                  * waker queue a list, woken_list, of
1951                                  * all the queues that reference the
1952                                  * waker queue through their
1953                                  * waker_bfqq pointer. When the waker
1954                                  * queue exits, the waker_bfqq pointer
1955                                  * of all the queues in the woken_list
1956                                  * is reset.
1957                                  *
1958                                  * In addition, if bfqq is already in
1959                                  * the woken_list of a waker queue,
1960                                  * then, before being inserted into
1961                                  * the woken_list of a new waker
1962                                  * queue, bfqq must be removed from
1963                                  * the woken_list of the old waker
1964                                  * queue.
1965                                  */
1966                                 if (!hlist_unhashed(&bfqq->woken_list_node))
1967                                         hlist_del_init(&bfqq->woken_list_node);
1968                                 hlist_add_head(&bfqq->woken_list_node,
1969                                     &bfqd->last_completed_rq_bfqq->woken_list);
1970 
1971                                 bfq_clear_bfqq_has_waker(bfqq);
1972                         } else if (bfqd->last_completed_rq_bfqq ==
1973                                    bfqq->waker_bfqq &&
1974                                    !bfq_bfqq_has_waker(bfqq)) {
1975                                 /*
1976                                  * synchronization with waker_bfqq
1977                                  * seen for the second time
1978                                  */
1979                                 bfq_mark_bfqq_has_waker(bfqq);
1980                         }
1981                 }
1982 
1983                 /*
1984                  * Periodically reset inject limit, to make sure that
1985                  * the latter eventually drops in case workload
1986                  * changes, see step (3) in the comments on
1987                  * bfq_update_inject_limit().
1988                  */
1989                 if (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
1990                                              msecs_to_jiffies(1000)))
1991                         bfq_reset_inject_limit(bfqd, bfqq);
1992 
1993                 /*
1994                  * The following conditions must hold to setup a new
1995                  * sampling of total service time, and then a new
1996                  * update of the inject limit:
1997                  * - bfqq is in service, because the total service
1998                  *   time is evaluated only for the I/O requests of
1999                  *   the queues in service;
2000                  * - this is the right occasion to compute or to
2001                  *   lower the baseline total service time, because
2002                  *   there are actually no requests in the drive,
2003                  *   or
2004                  *   the baseline total service time is available, and
2005                  *   this is the right occasion to compute the other
2006                  *   quantity needed to update the inject limit, i.e.,
2007                  *   the total service time caused by the amount of
2008                  *   injection allowed by the current value of the
2009                  *   limit. It is the right occasion because injection
2010                  *   has actually been performed during the service
2011                  *   hole, and there are still in-flight requests,
2012                  *   which are very likely to be exactly the injected
2013                  *   requests, or part of them;
2014                  * - the minimum interval for sampling the total
2015                  *   service time and updating the inject limit has
2016                  *   elapsed.
2017                  */
2018                 if (bfqq == bfqd->in_service_queue &&
2019                     (bfqd->rq_in_driver == 0 ||
2020                      (bfqq->last_serv_time_ns > 0 &&
2021                       bfqd->rqs_injected && bfqd->rq_in_driver > 0)) &&
2022                     time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2023                                               msecs_to_jiffies(10))) {
2024                         bfqd->last_empty_occupied_ns = ktime_get_ns();
2025                         /*
2026                          * Start the state machine for measuring the
2027                          * total service time of rq: setting
2028                          * wait_dispatch will cause bfqd->waited_rq to
2029                          * be set when rq will be dispatched.
2030                          */
2031                         bfqd->wait_dispatch = true;
2032                         /*
2033                          * If there is no I/O in service in the drive,
2034                          * then possible injection occurred before the
2035                          * arrival of rq will not affect the total
2036                          * service time of rq. So the injection limit
2037                          * must not be updated as a function of such
2038                          * total service time, unless new injection
2039                          * occurs before rq is completed. To have the
2040                          * injection limit updated only in the latter
2041                          * case, reset rqs_injected here (rqs_injected
2042                          * will be set in case injection is performed
2043                          * on bfqq before rq is completed).
2044                          */
2045                         if (bfqd->rq_in_driver == 0)
2046                                 bfqd->rqs_injected = false;
2047                 }
2048         }
2049 
2050         elv_rb_add(&bfqq->sort_list, rq);
2051 
2052         /*
2053          * Check if this request is a better next-serve candidate.
2054          */
2055         prev = bfqq->next_rq;
2056         next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
2057         bfqq->next_rq = next_rq;
2058 
2059         /*
2060          * Adjust priority tree position, if next_rq changes.
2061          * See comments on bfq_pos_tree_add_move() for the unlikely().
2062          */
2063         if (unlikely(!bfqd->nonrot_with_queueing && prev != bfqq->next_rq))
2064                 bfq_pos_tree_add_move(bfqd, bfqq);
2065 
2066         if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
2067                 bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
2068                                                  rq, &interactive);
2069         else {
2070                 if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
2071                     time_is_before_jiffies(
2072                                 bfqq->last_wr_start_finish +
2073                                 bfqd->bfq_wr_min_inter_arr_async)) {
2074                         bfqq->wr_coeff = bfqd->bfq_wr_coeff;
2075                         bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
2076 
2077                         bfqd->wr_busy_queues++;
2078                         bfqq->entity.prio_changed = 1;
2079                 }
2080                 if (prev != bfqq->next_rq)
2081                         bfq_updated_next_req(bfqd, bfqq);
2082         }
2083 
2084         /*
2085          * Assign jiffies to last_wr_start_finish in the following
2086          * cases:
2087          *
2088          * . if bfqq is not going to be weight-raised, because, for
2089          *   non weight-raised queues, last_wr_start_finish stores the
2090          *   arrival time of the last request; as of now, this piece
2091          *   of information is used only for deciding whether to
2092          *   weight-raise async queues
2093          *
2094          * . if bfqq is not weight-raised, because, if bfqq is now
2095          *   switching to weight-raised, then last_wr_start_finish
2096          *   stores the time when weight-raising starts
2097          *
2098          * . if bfqq is interactive, because, regardless of whether
2099          *   bfqq is currently weight-raised, the weight-raising
2100          *   period must start or restart (this case is considered
2101          *   separately because it is not detected by the above
2102          *   conditions, if bfqq is already weight-raised)
2103          *
2104          * last_wr_start_finish has to be updated also if bfqq is soft
2105          * real-time, because the weight-raising period is constantly
2106          * restarted on idle-to-busy transitions for these queues, but
2107          * this is already done in bfq_bfqq_handle_idle_busy_switch if
2108          * needed.
2109          */
2110         if (bfqd->low_latency &&
2111                 (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
2112                 bfqq->last_wr_start_finish = jiffies;
2113 }
2114 
2115 static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
2116                                           struct bio *bio,
2117                                           struct request_queue *q)
2118 {
2119         struct bfq_queue *bfqq = bfqd->bio_bfqq;
2120 
2121 
2122         if (bfqq)
2123                 return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
2124 
2125         return NULL;
2126 }
2127 
2128 static sector_t get_sdist(sector_t last_pos, struct request *rq)
2129 {
2130         if (last_pos)
2131                 return abs(blk_rq_pos(rq) - last_pos);
2132 
2133         return 0;
2134 }
2135 
2136 #if 0 /* Still not clear if we can do without next two functions */
2137 static void bfq_activate_request(struct request_queue *q, struct request *rq)
2138 {
2139         struct bfq_data *bfqd = q->elevator->elevator_data;
2140 
2141         bfqd->rq_in_driver++;
2142 }
2143 
2144 static void bfq_deactivate_request(struct request_queue *q, struct request *rq)
2145 {
2146         struct bfq_data *bfqd = q->elevator->elevator_data;
2147 
2148         bfqd->rq_in_driver--;
2149 }
2150 #endif
2151 
2152 static void bfq_remove_request(struct request_queue *q,
2153                                struct request *rq)
2154 {
2155         struct bfq_queue *bfqq = RQ_BFQQ(rq);
2156         struct bfq_data *bfqd = bfqq->bfqd;
2157         const int sync = rq_is_sync(rq);
2158 
2159         if (bfqq->next_rq == rq) {
2160                 bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
2161                 bfq_updated_next_req(bfqd, bfqq);
2162         }
2163 
2164         if (rq->queuelist.prev != &rq->queuelist)
2165                 list_del_init(&rq->queuelist);
2166         bfqq->queued[sync]--;
2167         bfqd->queued--;
2168         elv_rb_del(&bfqq->sort_list, rq);
2169 
2170         elv_rqhash_del(q, rq);
2171         if (q->last_merge == rq)
2172                 q->last_merge = NULL;
2173 
2174         if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
2175                 bfqq->next_rq = NULL;
2176 
2177                 if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
2178                         bfq_del_bfqq_busy(bfqd, bfqq, false);
2179                         /*
2180                          * bfqq emptied. In normal operation, when
2181                          * bfqq is empty, bfqq->entity.service and
2182                          * bfqq->entity.budget must contain,
2183                          * respectively, the service received and the
2184                          * budget used last time bfqq emptied. These
2185                          * facts do not hold in this case, as at least
2186                          * this last removal occurred while bfqq is
2187                          * not in service. To avoid inconsistencies,
2188                          * reset both bfqq->entity.service and
2189                          * bfqq->entity.budget, if bfqq has still a
2190                          * process that may issue I/O requests to it.
2191                          */
2192                         bfqq->entity.budget = bfqq->entity.service = 0;
2193                 }
2194 
2195                 /*
2196                  * Remove queue from request-position tree as it is empty.
2197                  */
2198                 if (bfqq->pos_root) {
2199                         rb_erase(&bfqq->pos_node, bfqq->pos_root);
2200                         bfqq->pos_root = NULL;
2201                 }
2202         } else {
2203                 /* see comments on bfq_pos_tree_add_move() for the unlikely() */
2204                 if (unlikely(!bfqd->nonrot_with_queueing))
2205                         bfq_pos_tree_add_move(bfqd, bfqq);
2206         }
2207 
2208         if (rq->cmd_flags & REQ_META)
2209                 bfqq->meta_pending--;
2210 
2211 }
2212 
2213 static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio,
2214                 unsigned int nr_segs)
2215 {
2216         struct request_queue *q = hctx->queue;
2217         struct bfq_data *bfqd = q->elevator->elevator_data;
2218         struct request *free = NULL;
2219         /*
2220          * bfq_bic_lookup grabs the queue_lock: invoke it now and
2221          * store its return value for later use, to avoid nesting
2222          * queue_lock inside the bfqd->lock. We assume that the bic
2223          * returned by bfq_bic_lookup does not go away before
2224          * bfqd->lock is taken.
2225          */
2226         struct bfq_io_cq *bic = bfq_bic_lookup(bfqd, current->io_context, q);
2227         bool ret;
2228 
2229         spin_lock_irq(&bfqd->lock);
2230 
2231         if (bic)
2232                 bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
2233         else
2234                 bfqd->bio_bfqq = NULL;
2235         bfqd->bio_bic = bic;
2236 
2237         ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free);
2238 
2239         if (free)
2240                 blk_mq_free_request(free);
2241         spin_unlock_irq(&bfqd->lock);
2242 
2243         return ret;
2244 }
2245 
2246 static int bfq_request_merge(struct request_queue *q, struct request **req,
2247                              struct bio *bio)
2248 {
2249         struct bfq_data *bfqd = q->elevator->elevator_data;
2250         struct request *__rq;
2251 
2252         __rq = bfq_find_rq_fmerge(bfqd, bio, q);
2253         if (__rq && elv_bio_merge_ok(__rq, bio)) {
2254                 *req = __rq;
2255                 return ELEVATOR_FRONT_MERGE;
2256         }
2257 
2258         return ELEVATOR_NO_MERGE;
2259 }
2260 
2261 static struct bfq_queue *bfq_init_rq(struct request *rq);
2262 
2263 static void bfq_request_merged(struct request_queue *q, struct request *req,
2264                                enum elv_merge type)
2265 {
2266         if (type == ELEVATOR_FRONT_MERGE &&
2267             rb_prev(&req->rb_node) &&
2268             blk_rq_pos(req) <
2269             blk_rq_pos(container_of(rb_prev(&req->rb_node),
2270                                     struct request, rb_node))) {
2271                 struct bfq_queue *bfqq = bfq_init_rq(req);
2272                 struct bfq_data *bfqd;
2273                 struct request *prev, *next_rq;
2274 
2275                 if (!bfqq)
2276                         return;
2277 
2278                 bfqd = bfqq->bfqd;
2279 
2280                 /* Reposition request in its sort_list */
2281                 elv_rb_del(&bfqq->sort_list, req);
2282                 elv_rb_add(&bfqq->sort_list, req);
2283 
2284                 /* Choose next request to be served for bfqq */
2285                 prev = bfqq->next_rq;
2286                 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
2287                                          bfqd->last_position);
2288                 bfqq->next_rq = next_rq;
2289                 /*
2290                  * If next_rq changes, update both the queue's budget to
2291                  * fit the new request and the queue's position in its
2292                  * rq_pos_tree.
2293                  */
2294                 if (prev != bfqq->next_rq) {
2295                         bfq_updated_next_req(bfqd, bfqq);
2296                         /*
2297                          * See comments on bfq_pos_tree_add_move() for
2298                          * the unlikely().
2299                          */
2300                         if (unlikely(!bfqd->nonrot_with_queueing))
2301                                 bfq_pos_tree_add_move(bfqd, bfqq);
2302                 }
2303         }
2304 }
2305 
2306 /*
2307  * This function is called to notify the scheduler that the requests
2308  * rq and 'next' have been merged, with 'next' going away.  BFQ
2309  * exploits this hook to address the following issue: if 'next' has a
2310  * fifo_time lower that rq, then the fifo_time of rq must be set to
2311  * the value of 'next', to not forget the greater age of 'next'.
2312  *
2313  * NOTE: in this function we assume that rq is in a bfq_queue, basing
2314  * on that rq is picked from the hash table q->elevator->hash, which,
2315  * in its turn, is filled only with I/O requests present in
2316  * bfq_queues, while BFQ is in use for the request queue q. In fact,
2317  * the function that fills this hash table (elv_rqhash_add) is called
2318  * only by bfq_insert_request.
2319  */
2320 static void bfq_requests_merged(struct request_queue *q, struct request *rq,
2321                                 struct request *next)
2322 {
2323         struct bfq_queue *bfqq = bfq_init_rq(rq),
2324                 *next_bfqq = bfq_init_rq(next);
2325 
2326         if (!bfqq)
2327                 return;
2328 
2329         /*
2330          * If next and rq belong to the same bfq_queue and next is older
2331          * than rq, then reposition rq in the fifo (by substituting next
2332          * with rq). Otherwise, if next and rq belong to different
2333          * bfq_queues, never reposition rq: in fact, we would have to
2334          * reposition it with respect to next's position in its own fifo,
2335          * which would most certainly be too expensive with respect to
2336          * the benefits.
2337          */
2338         if (bfqq == next_bfqq &&
2339             !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
2340             next->fifo_time < rq->fifo_time) {
2341                 list_del_init(&rq->queuelist);
2342                 list_replace_init(&next->queuelist, &rq->queuelist);
2343                 rq->fifo_time = next->fifo_time;
2344         }
2345 
2346         if (bfqq->next_rq == next)
2347                 bfqq->next_rq = rq;
2348 
2349         bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
2350 }
2351 
2352 /* Must be called with bfqq != NULL */
2353 static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
2354 {
2355         if (bfq_bfqq_busy(bfqq))
2356                 bfqq->bfqd->wr_busy_queues--;
2357         bfqq->wr_coeff = 1;
2358         bfqq->wr_cur_max_time = 0;
2359         bfqq->last_wr_start_finish = jiffies;
2360         /*
2361          * Trigger a weight change on the next invocation of
2362          * __bfq_entity_update_weight_prio.
2363          */
2364         bfqq->entity.prio_changed = 1;
2365 }
2366 
2367 void bfq_end_wr_async_queues(struct bfq_data *bfqd,
2368                              struct bfq_group *bfqg)
2369 {
2370         int i, j;
2371 
2372         for (i = 0; i < 2; i++)
2373                 for (j = 0; j < IOPRIO_BE_NR; j++)
2374                         if (bfqg->async_bfqq[i][j])
2375                                 bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]);
2376         if (bfqg->async_idle_bfqq)
2377                 bfq_bfqq_end_wr(bfqg->async_idle_bfqq);
2378 }
2379 
2380 static void bfq_end_wr(struct bfq_data *bfqd)
2381 {
2382         struct bfq_queue *bfqq;
2383 
2384         spin_lock_irq(&bfqd->lock);
2385 
2386         list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
2387                 bfq_bfqq_end_wr(bfqq);
2388         list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
2389                 bfq_bfqq_end_wr(bfqq);
2390         bfq_end_wr_async(bfqd);
2391 
2392         spin_unlock_irq(&bfqd->lock);
2393 }
2394 
2395 static sector_t bfq_io_struct_pos(void *io_struct, bool request)
2396 {
2397         if (request)
2398                 return blk_rq_pos(io_struct);
2399         else
2400                 return ((struct bio *)io_struct)->bi_iter.bi_sector;
2401 }
2402 
2403 static int bfq_rq_close_to_sector(void *io_struct, bool request,
2404                                   sector_t sector)
2405 {
2406         return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
2407                BFQQ_CLOSE_THR;
2408 }
2409 
2410 static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
2411                                          struct bfq_queue *bfqq,
2412                                          sector_t sector)
2413 {
2414         struct rb_root *root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
2415         struct rb_node *parent, *node;
2416         struct bfq_queue *__bfqq;
2417 
2418         if (RB_EMPTY_ROOT(root))
2419                 return NULL;
2420 
2421         /*
2422          * First, if we find a request starting at the end of the last
2423          * request, choose it.
2424          */
2425         __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL);
2426         if (__bfqq)
2427                 return __bfqq;
2428 
2429         /*
2430          * If the exact sector wasn't found, the parent of the NULL leaf
2431          * will contain the closest sector (rq_pos_tree sorted by
2432          * next_request position).
2433          */
2434         __bfqq = rb_entry(parent, struct bfq_queue, pos_node);
2435         if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2436                 return __bfqq;
2437 
2438         if (blk_rq_pos(__bfqq->next_rq) < sector)
2439                 node = rb_next(&__bfqq->pos_node);
2440         else
2441                 node = rb_prev(&__bfqq->pos_node);
2442         if (!node)
2443                 return NULL;
2444 
2445         __bfqq = rb_entry(node, struct bfq_queue, pos_node);
2446         if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2447                 return __bfqq;
2448 
2449         return NULL;
2450 }
2451 
2452 static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
2453                                                    struct bfq_queue *cur_bfqq,
2454                                                    sector_t sector)
2455 {
2456         struct bfq_queue *bfqq;
2457 
2458         /*
2459          * We shall notice if some of the queues are cooperating,
2460          * e.g., working closely on the same area of the device. In
2461          * that case, we can group them together and: 1) don't waste
2462          * time idling, and 2) serve the union of their requests in
2463          * the best possible order for throughput.
2464          */
2465         bfqq = bfqq_find_close(bfqd, cur_bfqq, sector);
2466         if (!bfqq || bfqq == cur_bfqq)
2467                 return NULL;
2468 
2469         return bfqq;
2470 }
2471 
2472 static struct bfq_queue *
2473 bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2474 {
2475         int process_refs, new_process_refs;
2476         struct bfq_queue *__bfqq;
2477 
2478         /*
2479          * If there are no process references on the new_bfqq, then it is
2480          * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
2481          * may have dropped their last reference (not just their last process
2482          * reference).
2483          */
2484         if (!bfqq_process_refs(new_bfqq))
2485                 return NULL;
2486 
2487         /* Avoid a circular list and skip interim queue merges. */
2488         while ((__bfqq = new_bfqq->new_bfqq)) {
2489                 if (__bfqq == bfqq)
2490                         return NULL;
2491                 new_bfqq = __bfqq;
2492         }
2493 
2494         process_refs = bfqq_process_refs(bfqq);
2495         new_process_refs = bfqq_process_refs(new_bfqq);
2496         /*
2497          * If the process for the bfqq has gone away, there is no
2498          * sense in merging the queues.
2499          */
2500         if (process_refs == 0 || new_process_refs == 0)
2501                 return NULL;
2502 
2503         bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
2504                 new_bfqq->pid);
2505 
2506         /*
2507          * Merging is just a redirection: the requests of the process
2508          * owning one of the two queues are redirected to the other queue.
2509          * The latter queue, in its turn, is set as shared if this is the
2510          * first time that the requests of some process are redirected to
2511          * it.
2512          *
2513          * We redirect bfqq to new_bfqq and not the opposite, because
2514          * we are in the context of the process owning bfqq, thus we
2515          * have the io_cq of this process. So we can immediately
2516          * configure this io_cq to redirect the requests of the
2517          * process to new_bfqq. In contrast, the io_cq of new_bfqq is
2518          * not available any more (new_bfqq->bic == NULL).
2519          *
2520          * Anyway, even in case new_bfqq coincides with the in-service
2521          * queue, redirecting requests the in-service queue is the
2522          * best option, as we feed the in-service queue with new
2523          * requests close to the last request served and, by doing so,
2524          * are likely to increase the throughput.
2525          */
2526         bfqq->new_bfqq = new_bfqq;
2527         new_bfqq->ref += process_refs;
2528         return new_bfqq;
2529 }
2530 
2531 static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
2532                                         struct bfq_queue *new_bfqq)
2533 {
2534         if (bfq_too_late_for_merging(new_bfqq))
2535                 return false;
2536 
2537         if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
2538             (bfqq->ioprio_class != new_bfqq->ioprio_class))
2539                 return false;
2540 
2541         /*
2542          * If either of the queues has already been detected as seeky,
2543          * then merging it with the other queue is unlikely to lead to
2544          * sequential I/O.
2545          */
2546         if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
2547                 return false;
2548 
2549         /*
2550          * Interleaved I/O is known to be done by (some) applications
2551          * only for reads, so it does not make sense to merge async
2552          * queues.
2553          */
2554         if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq))
2555                 return false;
2556 
2557         return true;
2558 }
2559 
2560 /*
2561  * Attempt to schedule a merge of bfqq with the currently in-service
2562  * queue or with a close queue among the scheduled queues.  Return
2563  * NULL if no merge was scheduled, a pointer to the shared bfq_queue
2564  * structure otherwise.
2565  *
2566  * The OOM queue is not allowed to participate to cooperation: in fact, since
2567  * the requests temporarily redirected to the OOM queue could be redirected
2568  * again to dedicated queues at any time, the state needed to correctly
2569  * handle merging with the OOM queue would be quite complex and expensive
2570  * to maintain. Besides, in such a critical condition as an out of memory,
2571  * the benefits of queue merging may be little relevant, or even negligible.
2572  *
2573  * WARNING: queue merging may impair fairness among non-weight raised
2574  * queues, for at least two reasons: 1) the original weight of a
2575  * merged queue may change during the merged state, 2) even being the
2576  * weight the same, a merged queue may be bloated with many more
2577  * requests than the ones produced by its originally-associated
2578  * process.
2579  */
2580 static struct bfq_queue *
2581 bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2582                      void *io_struct, bool request)
2583 {
2584         struct bfq_queue *in_service_bfqq, *new_bfqq;
2585 
2586         /*
2587          * Do not perform queue merging if the device is non
2588          * rotational and performs internal queueing. In fact, such a
2589          * device reaches a high speed through internal parallelism
2590          * and pipelining. This means that, to reach a high
2591          * throughput, it must have many requests enqueued at the same
2592          * time. But, in this configuration, the internal scheduling
2593          * algorithm of the device does exactly the job of queue
2594          * merging: it reorders requests so as to obtain as much as
2595          * possible a sequential I/O pattern. As a consequence, with
2596          * the workload generated by processes doing interleaved I/O,
2597          * the throughput reached by the device is likely to be the
2598          * same, with and without queue merging.
2599          *
2600          * Disabling merging also provides a remarkable benefit in
2601          * terms of throughput. Merging tends to make many workloads
2602          * artificially more uneven, because of shared queues
2603          * remaining non empty for incomparably more time than
2604          * non-merged queues. This may accentuate workload
2605          * asymmetries. For example, if one of the queues in a set of
2606          * merged queues has a higher weight than a normal queue, then
2607          * the shared queue may inherit such a high weight and, by
2608          * staying almost always active, may force BFQ to perform I/O
2609          * plugging most of the time. This evidently makes it harder
2610          * for BFQ to let the device reach a high throughput.
2611          *
2612          * Finally, the likely() macro below is not used because one
2613          * of the two branches is more likely than the other, but to
2614          * have the code path after the following if() executed as
2615          * fast as possible for the case of a non rotational device
2616          * with queueing. We want it because this is the fastest kind
2617          * of device. On the opposite end, the likely() may lengthen
2618          * the execution time of BFQ for the case of slower devices
2619          * (rotational or at least without queueing). But in this case
2620          * the execution time of BFQ matters very little, if not at
2621          * all.
2622          */
2623         if (likely(bfqd->nonrot_with_queueing))
2624                 return NULL;
2625 
2626         /*
2627          * Prevent bfqq from being merged if it has been created too
2628          * long ago. The idea is that true cooperating processes, and
2629          * thus their associated bfq_queues, are supposed to be
2630          * created shortly after each other. This is the case, e.g.,
2631          * for KVM/QEMU and dump I/O threads. Basing on this
2632          * assumption, the following filtering greatly reduces the
2633          * probability that two non-cooperating processes, which just
2634          * happen to do close I/O for some short time interval, have
2635          * their queues merged by mistake.
2636          */
2637         if (bfq_too_late_for_merging(bfqq))
2638                 return NULL;
2639 
2640         if (bfqq->new_bfqq)
2641                 return bfqq->new_bfqq;
2642 
2643         if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
2644                 return NULL;
2645 
2646         /* If there is only one backlogged queue, don't search. */
2647         if (bfq_tot_busy_queues(bfqd) == 1)
2648                 return NULL;
2649 
2650         in_service_bfqq = bfqd->in_service_queue;
2651 
2652         if (in_service_bfqq && in_service_bfqq != bfqq &&
2653             likely(in_service_bfqq != &bfqd->oom_bfqq) &&
2654             bfq_rq_close_to_sector(io_struct, request,
2655                                    bfqd->in_serv_last_pos) &&
2656             bfqq->entity.parent == in_service_bfqq->entity.parent &&
2657             bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
2658                 new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
2659                 if (new_bfqq)
2660                         return new_bfqq;
2661         }
2662         /*
2663          * Check whether there is a cooperator among currently scheduled
2664          * queues. The only thing we need is that the bio/request is not
2665          * NULL, as we need it to establish whether a cooperator exists.
2666          */
2667         new_bfqq = bfq_find_close_cooperator(bfqd, bfqq,
2668                         bfq_io_struct_pos(io_struct, request));
2669 
2670         if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) &&
2671             bfq_may_be_close_cooperator(bfqq, new_bfqq))
2672                 return bfq_setup_merge(bfqq, new_bfqq);
2673 
2674         return NULL;
2675 }
2676 
2677 static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
2678 {
2679         struct bfq_io_cq *bic = bfqq->bic;
2680 
2681         /*
2682          * If !bfqq->bic, the queue is already shared or its requests
2683          * have already been redirected to a shared queue; both idle window
2684          * and weight raising state have already been saved. Do nothing.
2685          */
2686         if (!bic)
2687                 return;
2688 
2689         bic->saved_weight = bfqq->entity.orig_weight;
2690         bic->saved_ttime = bfqq->ttime;
2691         bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
2692         bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
2693         bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
2694         bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
2695         if (unlikely(bfq_bfqq_just_created(bfqq) &&
2696                      !bfq_bfqq_in_large_burst(bfqq) &&
2697                      bfqq->bfqd->low_latency)) {
2698                 /*
2699                  * bfqq being merged right after being created: bfqq
2700                  * would have deserved interactive weight raising, but
2701                  * did not make it to be set in a weight-raised state,
2702                  * because of this early merge. Store directly the
2703                  * weight-raising state that would have been assigned
2704                  * to bfqq, so that to avoid that bfqq unjustly fails
2705                  * to enjoy weight raising if split soon.
2706                  */
2707                 bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
2708                 bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now();
2709                 bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
2710                 bic->saved_last_wr_start_finish = jiffies;
2711         } else {
2712                 bic->saved_wr_coeff = bfqq->wr_coeff;
2713                 bic->saved_wr_start_at_switch_to_srt =
2714                         bfqq->wr_start_at_switch_to_srt;
2715                 bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
2716                 bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
2717         }
2718 }
2719 
2720 void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq)
2721 {
2722         /*
2723          * To prevent bfqq's service guarantees from being violated,
2724          * bfqq may be left busy, i.e., queued for service, even if
2725          * empty (see comments in __bfq_bfqq_expire() for
2726          * details). But, if no process will send requests to bfqq any
2727          * longer, then there is no point in keeping bfqq queued for
2728          * service. In addition, keeping bfqq queued for service, but
2729          * with no process ref any longer, may have caused bfqq to be
2730          * freed when dequeued from service. But this is assumed to
2731          * never happen.
2732          */
2733         if (bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list) &&
2734             bfqq != bfqd->in_service_queue)
2735                 bfq_del_bfqq_busy(bfqd, bfqq, false);
2736 
2737         bfq_put_queue(bfqq);
2738 }
2739 
2740 static void
2741 bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
2742                 struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2743 {
2744         bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
2745                 (unsigned long)new_bfqq->pid);
2746         /* Save weight raising and idle window of the merged queues */
2747         bfq_bfqq_save_state(bfqq);
2748         bfq_bfqq_save_state(new_bfqq);
2749         if (bfq_bfqq_IO_bound(bfqq))
2750                 bfq_mark_bfqq_IO_bound(new_bfqq);
2751         bfq_clear_bfqq_IO_bound(bfqq);
2752 
2753         /*
2754          * If bfqq is weight-raised, then let new_bfqq inherit
2755          * weight-raising. To reduce false positives, neglect the case
2756          * where bfqq has just been created, but has not yet made it
2757          * to be weight-raised (which may happen because EQM may merge
2758          * bfqq even before bfq_add_request is executed for the first
2759          * time for bfqq). Handling this case would however be very
2760          * easy, thanks to the flag just_created.
2761          */
2762         if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
2763                 new_bfqq->wr_coeff = bfqq->wr_coeff;
2764                 new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
2765                 new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
2766                 new_bfqq->wr_start_at_switch_to_srt =
2767                         bfqq->wr_start_at_switch_to_srt;
2768                 if (bfq_bfqq_busy(new_bfqq))
2769                         bfqd->wr_busy_queues++;
2770                 new_bfqq->entity.prio_changed = 1;
2771         }
2772 
2773         if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
2774                 bfqq->wr_coeff = 1;
2775                 bfqq->entity.prio_changed = 1;
2776                 if (bfq_bfqq_busy(bfqq))
2777                         bfqd->wr_busy_queues--;
2778         }
2779 
2780         bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
2781                      bfqd->wr_busy_queues);
2782 
2783         /*
2784          * Merge queues (that is, let bic redirect its requests to new_bfqq)
2785          */
2786         bic_set_bfqq(bic, new_bfqq, 1);
2787         bfq_mark_bfqq_coop(new_bfqq);
2788         /*
2789          * new_bfqq now belongs to at least two bics (it is a shared queue):
2790          * set new_bfqq->bic to NULL. bfqq either:
2791          * - does not belong to any bic any more, and hence bfqq->bic must
2792          *   be set to NULL, or
2793          * - is a queue whose owning bics have already been redirected to a
2794          *   different queue, hence the queue is destined to not belong to
2795          *   any bic soon and bfqq->bic is already NULL (therefore the next
2796          *   assignment causes no harm).
2797          */
2798         new_bfqq->bic = NULL;
2799         /*
2800          * If the queue is shared, the pid is the pid of one of the associated
2801          * processes. Which pid depends on the exact sequence of merge events
2802          * the queue underwent. So printing such a pid is useless and confusing
2803          * because it reports a random pid between those of the associated
2804          * processes.
2805          * We mark such a queue with a pid -1, and then print SHARED instead of
2806          * a pid in logging messages.
2807          */
2808         new_bfqq->pid = -1;
2809         bfqq->bic = NULL;
2810         bfq_release_process_ref(bfqd, bfqq);
2811 }
2812 
2813 static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
2814                                 struct bio *bio)
2815 {
2816         struct bfq_data *bfqd = q->elevator->elevator_data;
2817         bool is_sync = op_is_sync(bio->bi_opf);
2818         struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
2819 
2820         /*
2821          * Disallow merge of a sync bio into an async request.
2822          */
2823         if (is_sync && !rq_is_sync(rq))
2824                 return false;
2825 
2826         /*
2827          * Lookup the bfqq that this bio will be queued with. Allow
2828          * merge only if rq is queued there.
2829          */
2830         if (!bfqq)
2831                 return false;
2832 
2833         /*
2834          * We take advantage of this function to perform an early merge
2835          * of the queues of possible cooperating processes.
2836          */
2837         new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false);
2838         if (new_bfqq) {
2839                 /*
2840                  * bic still points to bfqq, then it has not yet been
2841                  * redirected to some other bfq_queue, and a queue
2842                  * merge between bfqq and new_bfqq can be safely
2843                  * fulfilled, i.e., bic can be redirected to new_bfqq
2844                  * and bfqq can be put.
2845                  */
2846                 bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
2847                                 new_bfqq);
2848                 /*
2849                  * If we get here, bio will be queued into new_queue,
2850                  * so use new_bfqq to decide whether bio and rq can be
2851                  * merged.
2852                  */
2853                 bfqq = new_bfqq;
2854 
2855                 /*
2856                  * Change also bqfd->bio_bfqq, as
2857                  * bfqd->bio_bic now points to new_bfqq, and
2858                  * this function may be invoked again (and then may
2859                  * use again bqfd->bio_bfqq).
2860                  */
2861                 bfqd->bio_bfqq = bfqq;
2862         }
2863 
2864         return bfqq == RQ_BFQQ(rq);
2865 }
2866 
2867 /*
2868  * Set the maximum time for the in-service queue to consume its
2869  * budget. This prevents seeky processes from lowering the throughput.
2870  * In practice, a time-slice service scheme is used with seeky
2871  * processes.
2872  */
2873 static void bfq_set_budget_timeout(struct bfq_data *bfqd,
2874                                    struct bfq_queue *bfqq)
2875 {
2876         unsigned int timeout_coeff;
2877 
2878         if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
2879                 timeout_coeff = 1;
2880         else
2881                 timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
2882 
2883         bfqd->last_budget_start = ktime_get();
2884 
2885         bfqq->budget_timeout = jiffies +
2886                 bfqd->bfq_timeout * timeout_coeff;
2887 }
2888 
2889 static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
2890                                        struct bfq_queue *bfqq)
2891 {
2892         if (bfqq) {
2893                 bfq_clear_bfqq_fifo_expire(bfqq);
2894 
2895                 bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
2896 
2897                 if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
2898                     bfqq->wr_coeff > 1 &&
2899                     bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
2900                     time_is_before_jiffies(bfqq->budget_timeout)) {
2901                         /*
2902                          * For soft real-time queues, move the start
2903                          * of the weight-raising period forward by the
2904                          * time the queue has not received any
2905                          * service. Otherwise, a relatively long
2906                          * service delay is likely to cause the
2907                          * weight-raising period of the queue to end,
2908                          * because of the short duration of the
2909                          * weight-raising period of a soft real-time
2910                          * queue.  It is worth noting that this move
2911                          * is not so dangerous for the other queues,
2912                          * because soft real-time queues are not
2913                          * greedy.
2914                          *
2915                          * To not add a further variable, we use the
2916                          * overloaded field budget_timeout to
2917                          * determine for how long the queue has not
2918                          * received service, i.e., how much time has
2919                          * elapsed since the queue expired. However,
2920                          * this is a little imprecise, because
2921                          * budget_timeout is set to jiffies if bfqq
2922                          * not only expires, but also remains with no
2923                          * request.
2924                          */
2925                         if (time_after(bfqq->budget_timeout,
2926                                        bfqq->last_wr_start_finish))
2927                                 bfqq->last_wr_start_finish +=
2928                                         jiffies - bfqq->budget_timeout;
2929                         else
2930                                 bfqq->last_wr_start_finish = jiffies;
2931                 }
2932 
2933                 bfq_set_budget_timeout(bfqd, bfqq);
2934                 bfq_log_bfqq(bfqd, bfqq,
2935                              "set_in_service_queue, cur-budget = %d",
2936                              bfqq->entity.budget);
2937         }
2938 
2939         bfqd->in_service_queue = bfqq;
2940 }
2941 
2942 /*
2943  * Get and set a new queue for service.
2944  */
2945 static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
2946 {
2947         struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
2948 
2949         __bfq_set_in_service_queue(bfqd, bfqq);
2950         return bfqq;
2951 }
2952 
2953 static void bfq_arm_slice_timer(struct bfq_data *bfqd)
2954 {
2955         struct bfq_queue *bfqq = bfqd->in_service_queue;
2956         u32 sl;
2957 
2958         bfq_mark_bfqq_wait_request(bfqq);
2959 
2960         /*
2961          * We don't want to idle for seeks, but we do want to allow
2962          * fair distribution of slice time for a process doing back-to-back
2963          * seeks. So allow a little bit of time for him to submit a new rq.
2964          */
2965         sl = bfqd->bfq_slice_idle;
2966         /*
2967          * Unless the queue is being weight-raised or the scenario is
2968          * asymmetric, grant only minimum idle time if the queue
2969          * is seeky. A long idling is preserved for a weight-raised
2970          * queue, or, more in general, in an asymmetric scenario,
2971          * because a long idling is needed for guaranteeing to a queue
2972          * its reserved share of the throughput (in particular, it is
2973          * needed if the queue has a higher weight than some other
2974          * queue).
2975          */
2976         if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
2977             !bfq_asymmetric_scenario(bfqd, bfqq))
2978                 sl = min_t(u64, sl, BFQ_MIN_TT);
2979         else if (bfqq->wr_coeff > 1)
2980                 sl = max_t(u32, sl, 20ULL * NSEC_PER_MSEC);
2981 
2982         bfqd->last_idling_start = ktime_get();
2983         bfqd->last_idling_start_jiffies = jiffies;
2984 
2985         hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
2986                       HRTIMER_MODE_REL);
2987         bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
2988 }
2989 
2990 /*
2991  * In autotuning mode, max_budget is dynamically recomputed as the
2992  * amount of sectors transferred in timeout at the estimated peak
2993  * rate. This enables BFQ to utilize a full timeslice with a full
2994  * budget, even if the in-service queue is served at peak rate. And
2995  * this maximises throughput with sequential workloads.
2996  */
2997 static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
2998 {
2999         return (u64)bfqd->peak_rate * USEC_PER_MSEC *
3000                 jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
3001 }
3002 
3003 /*
3004  * Update parameters related to throughput and responsiveness, as a
3005  * function of the estimated peak rate. See comments on
3006  * bfq_calc_max_budget(), and on the ref_wr_duration array.
3007  */
3008 static void update_thr_responsiveness_params(struct bfq_data *bfqd)
3009 {
3010         if (bfqd->bfq_user_max_budget == 0) {
3011                 bfqd->bfq_max_budget =
3012                         bfq_calc_max_budget(bfqd);
3013                 bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget);
3014         }
3015 }
3016 
3017 static void bfq_reset_rate_computation(struct bfq_data *bfqd,
3018                                        struct request *rq)
3019 {
3020         if (rq != NULL) { /* new rq dispatch now, reset accordingly */
3021                 bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
3022                 bfqd->peak_rate_samples = 1;
3023                 bfqd->sequential_samples = 0;
3024                 bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
3025                         blk_rq_sectors(rq);
3026         } else /* no new rq dispatched, just reset the number of samples */
3027                 bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
3028 
3029         bfq_log(bfqd,
3030                 "reset_rate_computation at end, sample %u/%u tot_sects %llu",
3031                 bfqd->peak_rate_samples, bfqd->sequential_samples,
3032                 bfqd->tot_sectors_dispatched);
3033 }
3034 
3035 static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
3036 {
3037         u32 rate, weight, divisor;
3038 
3039         /*
3040          * For the convergence property to hold (see comments on
3041          * bfq_update_peak_rate()) and for the assessment to be
3042          * reliable, a minimum number of samples must be present, and
3043          * a minimum amount of time must have elapsed. If not so, do
3044          * not compute new rate. Just reset parameters, to get ready
3045          * for a new evaluation attempt.
3046          */
3047         if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
3048             bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
3049                 goto reset_computation;
3050 
3051         /*
3052          * If a new request completion has occurred after last
3053          * dispatch, then, to approximate the rate at which requests
3054          * have been served by the device, it is more precise to
3055          * extend the observation interval to the last completion.
3056          */
3057         bfqd->delta_from_first =
3058                 max_t(u64, bfqd->delta_from_first,
3059                       bfqd->last_completion - bfqd->first_dispatch);
3060 
3061         /*
3062          * Rate computed in sects/usec, and not sects/nsec, for
3063          * precision issues.
3064          */
3065         rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
3066                         div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
3067 
3068         /*
3069          * Peak rate not updated if:
3070          * - the percentage of sequential dispatches is below 3/4 of the
3071          *   total, and rate is below the current estimated peak rate
3072          * - rate is unreasonably high (> 20M sectors/sec)
3073          */
3074         if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
3075              rate <= bfqd->peak_rate) ||
3076                 rate > 20<<BFQ_RATE_SHIFT)
3077                 goto reset_computation;
3078 
3079         /*
3080          * We have to update the peak rate, at last! To this purpose,
3081          * we use a low-pass filter. We compute the smoothing constant
3082          * of the filter as a function of the 'weight' of the new
3083          * measured rate.
3084          *
3085          * As can be seen in next formulas, we define this weight as a
3086          * quantity proportional to how sequential the workload is,
3087          * and to how long the observation time interval is.
3088          *
3089          * The weight runs from 0 to 8. The maximum value of the
3090          * weight, 8, yields the minimum value for the smoothing
3091          * constant. At this minimum value for the smoothing constant,
3092          * the measured rate contributes for half of the next value of
3093          * the estimated peak rate.
3094          *
3095          * So, the first step is to compute the weight as a function
3096          * of how sequential the workload is. Note that the weight
3097          * cannot reach 9, because bfqd->sequential_samples cannot
3098          * become equal to bfqd->peak_rate_samples, which, in its
3099          * turn, holds true because bfqd->sequential_samples is not
3100          * incremented for the first sample.
3101          */
3102         weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
3103 
3104         /*
3105          * Second step: further refine the weight as a function of the
3106          * duration of the observation interval.
3107          */
3108         weight = min_t(u32, 8,
3109                        div_u64(weight * bfqd->delta_from_first,
3110                                BFQ_RATE_REF_INTERVAL));
3111 
3112         /*
3113          * Divisor ranging from 10, for minimum weight, to 2, for
3114          * maximum weight.
3115          */
3116         divisor = 10 - weight;
3117 
3118         /*
3119          * Finally, update peak rate:
3120          *
3121          * peak_rate = peak_rate * (divisor-1) / divisor  +  rate / divisor
3122          */
3123         bfqd->peak_rate *= divisor-1;
3124         bfqd->peak_rate /= divisor;
3125         rate /= divisor; /* smoothing constant alpha = 1/divisor */
3126 
3127         bfqd->peak_rate += rate;
3128 
3129         /*
3130          * For a very slow device, bfqd->peak_rate can reach 0 (see
3131          * the minimum representable values reported in the comments
3132          * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
3133          * divisions by zero where bfqd->peak_rate is used as a
3134          * divisor.
3135          */
3136         bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
3137 
3138         update_thr_responsiveness_params(bfqd);
3139 
3140 reset_computation:
3141         bfq_reset_rate_computation(bfqd, rq);
3142 }
3143 
3144 /*
3145  * Update the read/write peak rate (the main quantity used for
3146  * auto-tuning, see update_thr_responsiveness_params()).
3147  *
3148  * It is not trivial to estimate the peak rate (correctly): because of
3149  * the presence of sw and hw queues between the scheduler and the
3150  * device components that finally serve I/O requests, it is hard to
3151  * say exactly when a given dispatched request is served inside the
3152  * device, and for how long. As a consequence, it is hard to know
3153  * precisely at what rate a given set of requests is actually served
3154  * by the device.
3155  *
3156  * On the opposite end, the dispatch time of any request is trivially
3157  * available, and, from this piece of information, the "dispatch rate"
3158  * of requests can be immediately computed. So, the idea in the next
3159  * function is to use what is known, namely request dispatch times
3160  * (plus, when useful, request completion times), to estimate what is
3161  * unknown, namely in-device request service rate.
3162  *
3163  * The main issue is that, because of the above facts, the rate at
3164  * which a certain set of requests is dispatched over a certain time
3165  * interval can vary greatly with respect to the rate at which the
3166  * same requests are then served. But, since the size of any
3167  * intermediate queue is limited, and the service scheme is lossless
3168  * (no request is silently dropped), the following obvious convergence
3169  * property holds: the number of requests dispatched MUST become
3170  * closer and closer to the number of requests completed as the
3171  * observation interval grows. This is the key property used in
3172  * the next function to estimate the peak service rate as a function
3173  * of the observed dispatch rate. The function assumes to be invoked
3174  * on every request dispatch.
3175  */
3176 static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
3177 {
3178         u64 now_ns = ktime_get_ns();
3179 
3180         if (bfqd->peak_rate_samples == 0) { /* first dispatch */
3181                 bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
3182                         bfqd->peak_rate_samples);
3183                 bfq_reset_rate_computation(bfqd, rq);
3184                 goto update_last_values; /* will add one sample */
3185         }
3186 
3187         /*
3188          * Device idle for very long: the observation interval lasting
3189          * up to this dispatch cannot be a valid observation interval
3190          * for computing a new peak rate (similarly to the late-
3191          * completion event in bfq_completed_request()). Go to
3192          * update_rate_and_reset to have the following three steps
3193          * taken:
3194          * - close the observation interval at the last (previous)
3195          *   request dispatch or completion
3196          * - compute rate, if possible, for that observation interval
3197          * - start a new observation interval with this dispatch
3198          */
3199         if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
3200             bfqd->rq_in_driver == 0)
3201                 goto update_rate_and_reset;
3202 
3203         /* Update sampling information */
3204         bfqd->peak_rate_samples++;
3205 
3206         if ((bfqd->rq_in_driver > 0 ||
3207                 now_ns - bfqd->last_completion < BFQ_MIN_TT)
3208             && !BFQ_RQ_SEEKY(bfqd, bfqd->last_position, rq))
3209                 bfqd->sequential_samples++;
3210 
3211         bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
3212 
3213         /* Reset max observed rq size every 32 dispatches */
3214         if (likely(bfqd->peak_rate_samples % 32))
3215                 bfqd->last_rq_max_size =
3216                         max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
3217         else
3218                 bfqd->last_rq_max_size = blk_rq_sectors(rq);
3219 
3220         bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
3221 
3222         /* Target observation interval not yet reached, go on sampling */
3223         if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
3224                 goto update_last_values;
3225 
3226 update_rate_and_reset:
3227         bfq_update_rate_reset(bfqd, rq);
3228 update_last_values:
3229         bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
3230         if (RQ_BFQQ(rq) == bfqd->in_service_queue)
3231                 bfqd->in_serv_last_pos = bfqd->last_position;
3232         bfqd->last_dispatch = now_ns;
3233 }
3234 
3235 /*
3236  * Remove request from internal lists.
3237  */
3238 static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
3239 {
3240         struct bfq_queue *bfqq = RQ_BFQQ(rq);
3241 
3242         /*
3243          * For consistency, the next instruction should have been
3244          * executed after removing the request from the queue and
3245          * dispatching it.  We execute instead this instruction before
3246          * bfq_remove_request() (and hence introduce a temporary
3247          * inconsistency), for efficiency.  In fact, should this
3248          * dispatch occur for a non in-service bfqq, this anticipated
3249          * increment prevents two counters related to bfqq->dispatched
3250          * from risking to be, first, uselessly decremented, and then
3251          * incremented again when the (new) value of bfqq->dispatched
3252          * happens to be taken into account.
3253          */
3254         bfqq->dispatched++;
3255         bfq_update_peak_rate(q->elevator->elevator_data, rq);
3256 
3257         bfq_remove_request(q, rq);
3258 }
3259 
3260 /*
3261  * There is a case where idling does not have to be performed for
3262  * throughput concerns, but to preserve the throughput share of
3263  * the process associated with bfqq.
3264  *
3265  * To introduce this case, we can note that allowing the drive
3266  * to enqueue more than one request at a time, and hence
3267  * delegating de facto final scheduling decisions to the
3268  * drive's internal scheduler, entails loss of control on the
3269  * actual request service order. In particular, the critical
3270  * situation is when requests from different processes happen
3271  * to be present, at the same time, in the internal queue(s)
3272  * of the drive. In such a situation, the drive, by deciding
3273  * the service order of the internally-queued requests, does
3274  * determine also the actual throughput distribution among
3275  * these processes. But the drive typically has no notion or
3276  * concern about per-process throughput distribution, and
3277  * makes its decisions only on a per-request basis. Therefore,
3278  * the service distribution enforced by the drive's internal
3279  * scheduler is likely to coincide with the desired throughput
3280  * distribution only in a completely symmetric, or favorably
3281  * skewed scenario where:
3282  * (i-a) each of these processes must get the same throughput as
3283  *       the others,
3284  * (i-b) in case (i-a) does not hold, it holds that the process
3285  *       associated with bfqq must receive a lower or equal
3286  *       throughput than any of the other processes;
3287  * (ii)  the I/O of each process has the same properties, in
3288  *       terms of locality (sequential or random), direction
3289  *       (reads or writes), request sizes, greediness
3290  *       (from I/O-bound to sporadic), and so on;
3291 
3292  * In fact, in such a scenario, the drive tends to treat the requests
3293  * of each process in about the same way as the requests of the
3294  * others, and thus to provide each of these processes with about the
3295  * same throughput.  This is exactly the desired throughput
3296  * distribution if (i-a) holds, or, if (i-b) holds instead, this is an
3297  * even more convenient distribution for (the process associated with)
3298  * bfqq.
3299  *
3300  * In contrast, in any asymmetric or unfavorable scenario, device
3301  * idling (I/O-dispatch plugging) is certainly needed to guarantee
3302  * that bfqq receives its assigned fraction of the device throughput
3303  * (see [1] for details).
3304  *
3305  * The problem is that idling may significantly reduce throughput with
3306  * certain combinations of types of I/O and devices. An important
3307  * example is sync random I/O on flash storage with command
3308  * queueing. So, unless bfqq falls in cases where idling also boosts
3309  * throughput, it is important to check conditions (i-a), i(-b) and
3310  * (ii) accurately, so as to avoid idling when not strictly needed for
3311  * service guarantees.
3312  *
3313  * Unfortunately, it is extremely difficult to thoroughly check
3314  * condition (ii). And, in case there are active groups, it becomes
3315  * very difficult to check conditions (i-a) and (i-b) too.  In fact,
3316  * if there are active groups, then, for conditions (i-a) or (i-b) to
3317  * become false 'indirectly', it is enough that an active group
3318  * contains more active processes or sub-groups than some other active
3319  * group. More precisely, for conditions (i-a) or (i-b) to become
3320  * false because of such a group, it is not even necessary that the
3321  * group is (still) active: it is sufficient that, even if the group
3322  * has become inactive, some of its descendant processes still have
3323  * some request already dispatched but still waiting for
3324  * completion. In fact, requests have still to be guaranteed their
3325  * share of the throughput even after being dispatched. In this
3326  * respect, it is easy to show that, if a group frequently becomes
3327  * inactive while still having in-flight requests, and if, when this
3328  * happens, the group is not considered in the calculation of whether
3329  * the scenario is asymmetric, then the group may fail to be
3330  * guaranteed its fair share of the throughput (basically because
3331  * idling may not be performed for the descendant processes of the
3332  * group, but it had to be).  We address this issue with the following
3333  * bi-modal behavior, implemented in the function
3334  * bfq_asymmetric_scenario().
3335  *
3336  * If there are groups with requests waiting for completion
3337  * (as commented above, some of these groups may even be
3338  * already inactive), then the scenario is tagged as
3339  * asymmetric, conservatively, without checking any of the
3340  * conditions (i-a), (i-b) or (ii). So the device is idled for bfqq.
3341  * This behavior matches also the fact that groups are created
3342  * exactly if controlling I/O is a primary concern (to
3343  * preserve bandwidth and latency guarantees).
3344  *
3345  * On the opposite end, if there are no groups with requests waiting
3346  * for completion, then only conditions (i-a) and (i-b) are actually
3347  * controlled, i.e., provided that conditions (i-a) or (i-b) holds,
3348  * idling is not performed, regardless of whether condition (ii)
3349  * holds.  In other words, only if conditions (i-a) and (i-b) do not
3350  * hold, then idling is allowed, and the device tends to be prevented
3351  * from queueing many requests, possibly of several processes. Since
3352  * there are no groups with requests waiting for completion, then, to
3353  * control conditions (i-a) and (i-b) it is enough to check just
3354  * whether all the queues with requests waiting for completion also
3355  * have the same weight.
3356  *
3357  * Not checking condition (ii) evidently exposes bfqq to the
3358  * risk of getting less throughput than its fair share.
3359  * However, for queues with the same weight, a further
3360  * mechanism, preemption, mitigates or even eliminates this
3361  * problem. And it does so without consequences on overall
3362  * throughput. This mechanism and its benefits are explained
3363  * in the next three paragraphs.
3364  *
3365  * Even if a queue, say Q, is expired when it remains idle, Q
3366  * can still preempt the new in-service queue if the next
3367  * request of Q arrives soon (see the comments on
3368  * bfq_bfqq_update_budg_for_activation). If all queues and
3369  * groups have the same weight, this form of preemption,
3370  * combined with the hole-recovery heuristic described in the
3371  * comments on function bfq_bfqq_update_budg_for_activation,
3372  * are enough to preserve a correct bandwidth distribution in
3373  * the mid term, even without idling. In fact, even if not
3374  * idling allows the internal queues of the device to contain
3375  * many requests, and thus to reorder requests, we can rather
3376  * safely assume that the internal scheduler still preserves a
3377  * minimum of mid-term fairness.
3378  *
3379  * More precisely, this preemption-based, idleless approach
3380  * provides fairness in terms of IOPS, and not sectors per
3381  * second. This can be seen with a simple example. Suppose
3382  * that there are two queues with the same weight, but that
3383  * the first queue receives requests of 8 sectors, while the
3384  * second queue receives requests of 1024 sectors. In
3385  * addition, suppose that each of the two queues contains at
3386  * most one request at a time, which implies that each queue
3387  * always remains idle after it is served. Finally, after
3388  * remaining idle, each queue receives very quickly a new
3389  * request. It follows that the two queues are served
3390  * alternatively, preempting each other if needed. This
3391  * implies that, although both queues have the same weight,
3392  * the queue with large requests receives a service that is
3393  * 1024/8 times as high as the service received by the other
3394  * queue.
3395  *
3396  * The motivation for using preemption instead of idling (for
3397  * queues with the same weight) is that, by not idling,
3398  * service guarantees are preserved (completely or at least in
3399  * part) without minimally sacrificing throughput. And, if
3400  * there is no active group, then the primary expectation for
3401  * this device is probably a high throughput.
3402  *
3403  * We are now left only with explaining the two sub-conditions in the
3404  * additional compound condition that is checked below for deciding
3405  * whether the scenario is asymmetric. To explain the first
3406  * sub-condition, we need to add that the function
3407  * bfq_asymmetric_scenario checks the weights of only
3408  * non-weight-raised queues, for efficiency reasons (see comments on
3409  * bfq_weights_tree_add()). Then the fact that bfqq is weight-raised
3410  * is checked explicitly here. More precisely, the compound condition
3411  * below takes into account also the fact that, even if bfqq is being
3412  * weight-raised, the scenario is still symmetric if all queues with
3413  * requests waiting for completion happen to be
3414  * weight-raised. Actually, we should be even more precise here, and
3415  * differentiate between interactive weight raising and soft real-time
3416  * weight raising.
3417  *
3418  * The second sub-condition checked in the compound condition is
3419  * whether there is a fair amount of already in-flight I/O not
3420  * belonging to bfqq. If so, I/O dispatching is to be plugged, for the
3421  * following reason. The drive may decide to serve in-flight
3422  * non-bfqq's I/O requests before bfqq's ones, thereby delaying the
3423  * arrival of new I/O requests for bfqq (recall that bfqq is sync). If
3424  * I/O-dispatching is not plugged, then, while bfqq remains empty, a
3425  * basically uncontrolled amount of I/O from other queues may be
3426  * dispatched too, possibly causing the service of bfqq's I/O to be
3427  * delayed even longer in the drive. This problem gets more and more
3428  * serious as the speed and the queue depth of the drive grow,
3429  * because, as these two quantities grow, the probability to find no
3430  * queue busy but many requests in flight grows too. By contrast,
3431  * plugging I/O dispatching minimizes the delay induced by already
3432  * in-flight I/O, and enables bfqq to recover the bandwidth it may
3433  * lose because of this delay.
3434  *
3435  * As a side note, it is worth considering that the above
3436  * device-idling countermeasures may however fail in the following
3437  * unlucky scenario: if I/O-dispatch plugging is (correctly) disabled
3438  * in a time period during which all symmetry sub-conditions hold, and
3439  * therefore the device is allowed to enqueue many requests, but at
3440  * some later point in time some sub-condition stops to hold, then it
3441  * may become impossible to make requests be served in the desired
3442  * order until all the requests already queued in the device have been
3443  * served. The last sub-condition commented above somewhat mitigates
3444  * this problem for weight-raised queues.
3445  */
3446 static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd,
3447                                                  struct bfq_queue *bfqq)
3448 {
3449         /* No point in idling for bfqq if it won't get requests any longer */
3450         if (unlikely(!bfqq_process_refs(bfqq)))
3451                 return false;
3452 
3453         return (bfqq->wr_coeff > 1 &&
3454                 (bfqd->wr_busy_queues <
3455                  bfq_tot_busy_queues(bfqd) ||
3456                  bfqd->rq_in_driver >=
3457                  bfqq->dispatched + 4)) ||
3458                 bfq_asymmetric_scenario(bfqd, bfqq);
3459 }
3460 
3461 static bool __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3462                               enum bfqq_expiration reason)
3463 {
3464         /*
3465          * If this bfqq is shared between multiple processes, check
3466          * to make sure that those processes are still issuing I/Os
3467          * within the mean seek distance. If not, it may be time to
3468          * break the queues apart again.
3469          */
3470         if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
3471                 bfq_mark_bfqq_split_coop(bfqq);
3472 
3473         /*
3474          * Consider queues with a higher finish virtual time than
3475          * bfqq. If idling_needed_for_service_guarantees(bfqq) returns
3476          * true, then bfqq's bandwidth would be violated if an
3477          * uncontrolled amount of I/O from these queues were
3478          * dispatched while bfqq is waiting for its new I/O to
3479          * arrive. This is exactly what may happen if this is a forced
3480          * expiration caused by a preemption attempt, and if bfqq is
3481          * not re-scheduled. To prevent this from happening, re-queue
3482          * bfqq if it needs I/O-dispatch plugging, even if it is
3483          * empty. By doing so, bfqq is granted to be served before the
3484          * above queues (provided that bfqq is of course eligible).
3485          */
3486         if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
3487             !(reason == BFQQE_PREEMPTED &&
3488               idling_needed_for_service_guarantees(bfqd, bfqq))) {
3489                 if (bfqq->dispatched == 0)
3490                         /*
3491                          * Overloading budget_timeout field to store
3492                          * the time at which the queue remains with no
3493                          * backlog and no outstanding request; used by
3494                          * the weight-raising mechanism.
3495                          */
3496                         bfqq->budget_timeout = jiffies;
3497 
3498                 bfq_del_bfqq_busy(bfqd, bfqq, true);
3499         } else {
3500                 bfq_requeue_bfqq(bfqd, bfqq, true);
3501                 /*
3502                  * Resort priority tree of potential close cooperators.
3503                  * See comments on bfq_pos_tree_add_move() for the unlikely().
3504                  */
3505                 if (unlikely(!bfqd->nonrot_with_queueing &&
3506                              !RB_EMPTY_ROOT(&bfqq->sort_list)))
3507                         bfq_pos_tree_add_move(bfqd, bfqq);
3508         }
3509 
3510         /*
3511          * All in-service entities must have been properly deactivated
3512          * or requeued before executing the next function, which
3513          * resets all in-service entities as no more in service. This
3514          * may cause bfqq to be freed. If this happens, the next
3515          * function returns true.
3516          */
3517         return __bfq_bfqd_reset_in_service(bfqd);
3518 }
3519 
3520 /**
3521  * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
3522  * @bfqd: device data.
3523  * @bfqq: queue to update.
3524  * @reason: reason for expiration.
3525  *
3526  * Handle the feedback on @bfqq budget at queue expiration.
3527  * See the body for detailed comments.
3528  */
3529 static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
3530                                      struct bfq_queue *bfqq,
3531                                      enum bfqq_expiration reason)
3532 {
3533         struct request *next_rq;
3534         int budget, min_budget;
3535 
3536         min_budget = bfq_min_budget(bfqd);
3537 
3538         if (bfqq->wr_coeff == 1)
3539                 budget = bfqq->max_budget;
3540         else /*
3541               * Use a constant, low budget for weight-raised queues,
3542               * to help achieve a low latency. Keep it slightly higher
3543               * than the minimum possible budget, to cause a little
3544               * bit fewer expirations.
3545               */
3546                 budget = 2 * min_budget;
3547 
3548         bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
3549                 bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
3550         bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
3551                 budget, bfq_min_budget(bfqd));
3552         bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
3553                 bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
3554 
3555         if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
3556                 switch (reason) {
3557                 /*
3558                  * Caveat: in all the following cases we trade latency
3559                  * for throughput.
3560                  */
3561                 case BFQQE_TOO_IDLE:
3562                         /*
3563                          * This is the only case where we may reduce
3564                          * the budget: if there is no request of the
3565                          * process still waiting for completion, then
3566                          * we assume (tentatively) that the timer has
3567                          * expired because the batch of requests of
3568                          * the process could have been served with a
3569                          * smaller budget.  Hence, betting that
3570                          * process will behave in the same way when it
3571                          * becomes backlogged again, we reduce its
3572                          * next budget.  As long as we guess right,
3573                          * this budget cut reduces the latency
3574                          * experienced by the process.
3575                          *
3576                          * However, if there are still outstanding
3577                          * requests, then the process may have not yet
3578                          * issued its next request just because it is
3579                          * still waiting for the completion of some of
3580                          * the still outstanding ones.  So in this
3581                          * subcase we do not reduce its budget, on the
3582                          * contrary we increase it to possibly boost
3583                          * the throughput, as discussed in the
3584                          * comments to the BUDGET_TIMEOUT case.
3585                          */
3586                         if (bfqq->dispatched > 0) /* still outstanding reqs */
3587                                 budget = min(budget * 2, bfqd->bfq_max_budget);
3588                         else {
3589                                 if (budget > 5 * min_budget)
3590                                         budget -= 4 * min_budget;
3591                                 else
3592                                         budget = min_budget;
3593                         }
3594                         break;
3595                 case BFQQE_BUDGET_TIMEOUT:
3596                         /*
3597                          * We double the budget here because it gives
3598                          * the chance to boost the throughput if this
3599                          * is not a seeky process (and has bumped into
3600                          * this timeout because of, e.g., ZBR).
3601                          */
3602                         budget = min(budget * 2, bfqd->bfq_max_budget);
3603                         break;
3604                 case BFQQE_BUDGET_EXHAUSTED:
3605                         /*
3606                          * The process still has backlog, and did not
3607                          * let either the budget timeout or the disk
3608                          * idling timeout expire. Hence it is not
3609                          * seeky, has a short thinktime and may be
3610                          * happy with a higher budget too. So
3611                          * definitely increase the budget of this good
3612                          * candidate to boost the disk throughput.
3613                          */
3614                         budget = min(budget * 4, bfqd->bfq_max_budget);
3615                         break;
3616                 case BFQQE_NO_MORE_REQUESTS:
3617                         /*
3618                          * For queues that expire for this reason, it
3619                          * is particularly important to keep the
3620                          * budget close to the actual service they
3621                          * need. Doing so reduces the timestamp
3622                          * misalignment problem described in the
3623                          * comments in the body of
3624                          * __bfq_activate_entity. In fact, suppose
3625                          * that a queue systematically expires for
3626                          * BFQQE_NO_MORE_REQUESTS and presents a
3627                          * new request in time to enjoy timestamp
3628                          * back-shifting. The larger the budget of the
3629                          * queue is with respect to the service the
3630                          * queue actually requests in each service
3631                          * slot, the more times the queue can be
3632                          * reactivated with the same virtual finish
3633                          * time. It follows that, even if this finish
3634                          * time is pushed to the system virtual time
3635                          * to reduce the consequent timestamp
3636                          * misalignment, the queue unjustly enjoys for
3637                          * many re-activations a lower finish time
3638                          * than all newly activated queues.
3639                          *
3640                          * The service needed by bfqq is measured
3641                          * quite precisely by bfqq->entity.service.
3642                          * Since bfqq does not enjoy device idling,
3643                          * bfqq->entity.service is equal to the number
3644                          * of sectors that the process associated with
3645                          * bfqq requested to read/write before waiting
3646                          * for request completions, or blocking for
3647                          * other reasons.
3648                          */
3649                         budget = max_t(int, bfqq->entity.service, min_budget);
3650                         break;
3651                 default:
3652                         return;
3653                 }
3654         } else if (!bfq_bfqq_sync(bfqq)) {
3655                 /*
3656                  * Async queues get always the maximum possible
3657                  * budget, as for them we do not care about latency
3658                  * (in addition, their ability to dispatch is limited
3659                  * by the charging factor).
3660                  */
3661                 budget = bfqd->bfq_max_budget;
3662         }
3663 
3664         bfqq->max_budget = budget;
3665 
3666         if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
3667             !bfqd->bfq_user_max_budget)
3668                 bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
3669 
3670         /*
3671          * If there is still backlog, then assign a new budget, making
3672          * sure that it is large enough for the next request.  Since
3673          * the finish time of bfqq must be kept in sync with the
3674          * budget, be sure to call __bfq_bfqq_expire() *after* this
3675          * update.
3676          *
3677          * If there is no backlog, then no need to update the budget;
3678          * it will be updated on the arrival of a new request.
3679          */
3680         next_rq = bfqq->next_rq;
3681         if (next_rq)
3682                 bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
3683                                             bfq_serv_to_charge(next_rq, bfqq));
3684 
3685         bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
3686                         next_rq ? blk_rq_sectors(next_rq) : 0,
3687                         bfqq->entity.budget);
3688 }
3689 
3690 /*
3691  * Return true if the process associated with bfqq is "slow". The slow
3692  * flag is used, in addition to the budget timeout, to reduce the
3693  * amount of service provided to seeky processes, and thus reduce
3694  * their chances to lower the throughput. More details in the comments
3695  * on the function bfq_bfqq_expire().
3696  *
3697  * An important observation is in order: as discussed in the comments
3698  * on the function bfq_update_peak_rate(), with devices with internal
3699  * queues, it is hard if ever possible to know when and for how long
3700  * an I/O request is processed by the device (apart from the trivial
3701  * I/O pattern where a new request is dispatched only after the
3702  * previous one has been completed). This makes it hard to evaluate
3703  * the real rate at which the I/O requests of each bfq_queue are
3704  * served.  In fact, for an I/O scheduler like BFQ, serving a
3705  * bfq_queue means just dispatching its requests during its service
3706  * slot (i.e., until the budget of the queue is exhausted, or the
3707  * queue remains idle, or, finally, a timeout fires). But, during the
3708  * service slot of a bfq_queue, around 100 ms at most, the device may
3709  * be even still processing requests of bfq_queues served in previous
3710  * service slots. On the opposite end, the requests of the in-service
3711  * bfq_queue may be completed after the service slot of the queue
3712  * finishes.
3713  *
3714  * Anyway, unless more sophisticated solutions are used
3715  * (where possible), the sum of the sizes of the requests dispatched
3716  * during the service slot of a bfq_queue is probably the only
3717  * approximation available for the service received by the bfq_queue
3718  * during its service slot. And this sum is the quantity used in this
3719  * function to evaluate the I/O speed of a process.
3720  */
3721 static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3722                                  bool compensate, enum bfqq_expiration reason,
3723                                  unsigned long *delta_ms)
3724 {
3725         ktime_t delta_ktime;
3726         u32 delta_usecs;
3727         bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
3728 
3729         if (!bfq_bfqq_sync(bfqq))
3730                 return false;
3731 
3732         if (compensate)
3733                 delta_ktime = bfqd->last_idling_start;
3734         else
3735                 delta_ktime = ktime_get();
3736         delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
3737         delta_usecs = ktime_to_us(delta_ktime);
3738 
3739         /* don't use too short time intervals */
3740         if (delta_usecs < 1000) {
3741                 if (blk_queue_nonrot(bfqd->queue))
3742                          /*
3743                           * give same worst-case guarantees as idling
3744                           * for seeky
3745                           */
3746                         *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
3747                 else /* charge at least one seek */
3748                         *delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
3749 
3750                 return slow;
3751         }
3752 
3753         *delta_ms = delta_usecs / USEC_PER_MSEC;
3754 
3755         /*
3756          * Use only long (> 20ms) intervals to filter out excessive
3757          * spikes in service rate estimation.
3758          */
3759         if (delta_usecs > 20000) {
3760                 /*
3761                  * Caveat for rotational devices: processes doing I/O
3762                  * in the slower disk zones tend to be slow(er) even
3763                  * if not seeky. In this respect, the estimated peak
3764                  * rate is likely to be an average over the disk
3765                  * surface. Accordingly, to not be too harsh with
3766                  * unlucky processes, a process is deemed slow only if
3767                  * its rate has been lower than half of the estimated
3768                  * peak rate.
3769                  */
3770                 slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
3771         }
3772 
3773         bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
3774 
3775         return slow;
3776 }
3777 
3778 /*
3779  * To be deemed as soft real-time, an application must meet two
3780  * requirements. First, the application must not require an average
3781  * bandwidth higher than the approximate bandwidth required to playback or
3782  * record a compressed high-definition video.
3783  * The next function is invoked on the completion of the last request of a
3784  * batch, to compute the next-start time instant, soft_rt_next_start, such
3785  * that, if the next request of the application does not arrive before
3786  * soft_rt_next_start, then the above requirement on the bandwidth is met.
3787  *
3788  * The second requirement is that the request pattern of the application is
3789  * isochronous, i.e., that, after issuing a request or a batch of requests,
3790  * the application stops issuing new requests until all its pending requests
3791  * have been completed. After that, the application may issue a new batch,
3792  * and so on.
3793  * For this reason the next function is invoked to compute
3794  * soft_rt_next_start only for applications that meet this requirement,
3795  * whereas soft_rt_next_start is set to infinity for applications that do
3796  * not.
3797  *
3798  * Unfortunately, even a greedy (i.e., I/O-bound) application may
3799  * happen to meet, occasionally or systematically, both the above
3800  * bandwidth and isochrony requirements. This may happen at least in
3801  * the following circumstances. First, if the CPU load is high. The
3802  * application may stop issuing requests while the CPUs are busy
3803  * serving other processes, then restart, then stop again for a while,
3804  * and so on. The other circumstances are related to the storage
3805  * device: the storage device is highly loaded or reaches a low-enough
3806  * throughput with the I/O of the application (e.g., because the I/O
3807  * is random and/or the device is slow). In all these cases, the
3808  * I/O of the application may be simply slowed down enough to meet
3809  * the bandwidth and isochrony requirements. To reduce the probability
3810  * that greedy applications are deemed as soft real-time in these
3811  * corner cases, a further rule is used in the computation of
3812  * soft_rt_next_start: the return value of this function is forced to
3813  * be higher than the maximum between the following two quantities.
3814  *
3815  * (a) Current time plus: (1) the maximum time for which the arrival
3816  *     of a request is waited for when a sync queue becomes idle,
3817  *     namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We
3818  *     postpone for a moment the reason for adding a few extra
3819  *     jiffies; we get back to it after next item (b).  Lower-bounding
3820  *     the return value of this function with the current time plus
3821  *     bfqd->bfq_slice_idle tends to filter out greedy applications,
3822  *     because the latter issue their next request as soon as possible
3823  *     after the last one has been completed. In contrast, a soft
3824  *     real-time application spends some time processing data, after a
3825  *     batch of its requests has been completed.
3826  *
3827  * (b) Current value of bfqq->soft_rt_next_start. As pointed out
3828  *     above, greedy applications may happen to meet both the
3829  *     bandwidth and isochrony requirements under heavy CPU or
3830  *     storage-device load. In more detail, in these scenarios, these
3831  *     applications happen, only for limited time periods, to do I/O
3832  *     slowly enough to meet all the requirements described so far,
3833  *     including the filtering in above item (a). These slow-speed
3834  *     time intervals are usually interspersed between other time
3835  *     intervals during which these applications do I/O at a very high
3836  *     speed. Fortunately, exactly because of the high speed of the
3837  *     I/O in the high-speed intervals, the values returned by this
3838  *     function happen to be so high, near the end of any such
3839  *     high-speed interval, to be likely to fall *after* the end of
3840  *     the low-speed time interval that follows. These high values are
3841  *     stored in bfqq->soft_rt_next_start after each invocation of
3842  *     this function. As a consequence, if the last value of
3843  *     bfqq->soft_rt_next_start is constantly used to lower-bound the
3844  *     next value that this function may return, then, from the very
3845  *     beginning of a low-speed interval, bfqq->soft_rt_next_start is
3846  *     likely to be constantly kept so high that any I/O request
3847  *     issued during the low-speed interval is considered as arriving
3848  *     to soon for the application to be deemed as soft
3849  *     real-time. Then, in the high-speed interval that follows, the
3850  *     application will not be deemed as soft real-time, just because
3851  *     it will do I/O at a high speed. And so on.
3852  *
3853  * Getting back to the filtering in item (a), in the following two
3854  * cases this filtering might be easily passed by a greedy
3855  * application, if the reference quantity was just
3856  * bfqd->bfq_slice_idle:
3857  * 1) HZ is so low that the duration of a jiffy is comparable to or
3858  *    higher than bfqd->bfq_slice_idle. This happens, e.g., on slow
3859  *    devices with HZ=100. The time granularity may be so coarse
3860  *    that the approximation, in jiffies, of bfqd->bfq_slice_idle
3861  *    is rather lower than the exact value.
3862  * 2) jiffies, instead of increasing at a constant rate, may stop increasing
3863  *    for a while, then suddenly 'jump' by several units to recover the lost
3864  *    increments. This seems to happen, e.g., inside virtual machines.
3865  * To address this issue, in the filtering in (a) we do not use as a
3866  * reference time interval just bfqd->bfq_slice_idle, but
3867  * bfqd->bfq_slice_idle plus a few jiffies. In particular, we add the
3868  * minimum number of jiffies for which the filter seems to be quite
3869  * precise also in embedded systems and KVM/QEMU virtual machines.
3870  */
3871 static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
3872                                                 struct bfq_queue *bfqq)
3873 {
3874         return max3(bfqq->soft_rt_next_start,
3875                     bfqq->last_idle_bklogged +
3876                     HZ * bfqq->service_from_backlogged /
3877                     bfqd->bfq_wr_max_softrt_rate,
3878                     jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
3879 }
3880 
3881 /**
3882  * bfq_bfqq_expire - expire a queue.
3883  * @bfqd: device owning the queue.
3884  * @bfqq: the queue to expire.
3885  * @compensate: if true, compensate for the time spent idling.
3886  * @reason: the reason causing the expiration.
3887  *
3888  * If the process associated with bfqq does slow I/O (e.g., because it
3889  * issues random requests), we charge bfqq with the time it has been
3890  * in service instead of the service it has received (see
3891  * bfq_bfqq_charge_time for details on how this goal is achieved). As
3892  * a consequence, bfqq will typically get higher timestamps upon
3893  * reactivation, and hence it will be rescheduled as if it had
3894  * received more service than what it has actually received. In the
3895  * end, bfqq receives less service in proportion to how slowly its
3896  * associated process consumes its budgets (and hence how seriously it
3897  * tends to lower the throughput). In addition, this time-charging
3898  * strategy guarantees time fairness among slow processes. In
3899  * contrast, if the process associated with bfqq is not slow, we
3900  * charge bfqq exactly with the service it has received.
3901  *
3902  * Charging time to the first type of queues and the exact service to
3903  * the other has the effect of using the WF2Q+ policy to schedule the
3904  * former on a timeslice basis, without violating service domain
3905  * guarantees among the latter.
3906  */
3907 void bfq_bfqq_expire(struct bfq_data *bfqd,
3908                      struct bfq_queue *bfqq,
3909                      bool compensate,
3910                      enum bfqq_expiration reason)
3911 {
3912         bool slow;
3913         unsigned long delta = 0;
3914         struct bfq_entity *entity = &bfqq->entity;
3915 
3916         /*
3917          * Check whether the process is slow (see bfq_bfqq_is_slow).
3918          */
3919         slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
3920 
3921         /*
3922          * As above explained, charge slow (typically seeky) and
3923          * timed-out queues with the time and not the service
3924          * received, to favor sequential workloads.
3925          *
3926          * Processes doing I/O in the slower disk zones will tend to
3927          * be slow(er) even if not seeky. Therefore, since the
3928          * estimated peak rate is actually an average over the disk
3929          * surface, these processes may timeout just for bad luck. To
3930          * avoid punishing them, do not charge time to processes that
3931          * succeeded in consuming at least 2/3 of their budget. This
3932          * allows BFQ to preserve enough elasticity to still perform
3933          * bandwidth, and not time, distribution with little unlucky
3934          * or quasi-sequential processes.
3935          */
3936         if (bfqq->wr_coeff == 1 &&
3937             (slow ||
3938              (reason == BFQQE_BUDGET_TIMEOUT &&
3939               bfq_bfqq_budget_left(bfqq) >=  entity->budget / 3)))
3940                 bfq_bfqq_charge_time(bfqd, bfqq, delta);
3941 
3942         if (reason == BFQQE_TOO_IDLE &&
3943             entity->service <= 2 * entity->budget / 10)
3944                 bfq_clear_bfqq_IO_bound(bfqq);
3945 
3946         if (bfqd->low_latency && bfqq->wr_coeff == 1)
3947                 bfqq->last_wr_start_finish = jiffies;
3948 
3949         if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
3950             RB_EMPTY_ROOT(&bfqq->sort_list)) {
3951                 /*
3952                  * If we get here, and there are no outstanding
3953                  * requests, then the request pattern is isochronous
3954                  * (see the comments on the function
3955                  * bfq_bfqq_softrt_next_start()). Thus we can compute
3956                  * soft_rt_next_start. And we do it, unless bfqq is in
3957                  * interactive weight raising. We do not do it in the
3958                  * latter subcase, for the following reason. bfqq may
3959                  * be conveying the I/O needed to load a soft
3960                  * real-time application. Such an application will
3961                  * actually exhibit a soft real-time I/O pattern after
3962                  * it finally starts doing its job. But, if
3963                  * soft_rt_next_start is computed here for an
3964                  * interactive bfqq, and bfqq had received a lot of
3965                  * service before remaining with no outstanding
3966                  * request (likely to happen on a fast device), then
3967                  * soft_rt_next_start would be assigned such a high
3968                  * value that, for a very long time, bfqq would be
3969                  * prevented from being possibly considered as soft
3970                  * real time.
3971                  *
3972                  * If, instead, the queue still has outstanding
3973                  * requests, then we have to wait for the completion
3974                  * of all the outstanding requests to discover whether
3975                  * the request pattern is actually isochronous.
3976                  */
3977                 if (bfqq->dispatched == 0 &&
3978                     bfqq->wr_coeff != bfqd->bfq_wr_coeff)
3979                         bfqq->soft_rt_next_start =
3980                                 bfq_bfqq_softrt_next_start(bfqd, bfqq);
3981                 else if (bfqq->dispatched > 0) {
3982                         /*
3983                          * Schedule an update of soft_rt_next_start to when
3984                          * the task may be discovered to be isochronous.
3985                          */
3986                         bfq_mark_bfqq_softrt_update(bfqq);
3987                 }
3988         }
3989 
3990         bfq_log_bfqq(bfqd, bfqq,
3991                 "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
3992                 slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
3993 
3994         /*
3995          * bfqq expired, so no total service time needs to be computed
3996          * any longer: reset state machine for measuring total service
3997          * times.
3998          */
3999         bfqd->rqs_injected = bfqd->wait_dispatch = false;
4000         bfqd->waited_rq = NULL;
4001 
4002         /*
4003          * Increase, decrease or leave budget unchanged according to
4004          * reason.
4005          */
4006         __bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
4007         if (__bfq_bfqq_expire(bfqd, bfqq, reason))
4008                 /* bfqq is gone, no more actions on it */
4009                 return;
4010 
4011         /* mark bfqq as waiting a request only if a bic still points to it */
4012         if (!bfq_bfqq_busy(bfqq) &&
4013             reason != BFQQE_BUDGET_TIMEOUT &&
4014             reason != BFQQE_BUDGET_EXHAUSTED) {
4015                 bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
4016                 /*
4017                  * Not setting service to 0, because, if the next rq
4018                  * arrives in time, the queue will go on receiving
4019                  * service with this same budget (as if it never expired)
4020                  */
4021         } else
4022                 entity->service = 0;
4023 
4024         /*
4025          * Reset the received-service counter for every parent entity.
4026          * Differently from what happens with bfqq->entity.service,
4027          * the resetting of this counter never needs to be postponed
4028          * for parent entities. In fact, in case bfqq may have a
4029          * chance to go on being served using the last, partially
4030          * consumed budget, bfqq->entity.service needs to be kept,
4031          * because if bfqq then actually goes on being served using
4032          * the same budget, the last value of bfqq->entity.service is
4033          * needed to properly decrement bfqq->entity.budget by the
4034          * portion already consumed. In contrast, it is not necessary
4035          * to keep entity->service for parent entities too, because
4036          * the bubble up of the new value of bfqq->entity.budget will
4037          * make sure that the budgets of parent entities are correct,
4038          * even in case bfqq and thus parent entities go on receiving
4039          * service with the same budget.
4040          */
4041         entity = entity->parent;
4042         for_each_entity(entity)
4043                 entity->service = 0;
4044 }
4045 
4046 /*
4047  * Budget timeout is not implemented through a dedicated timer, but
4048  * just checked on request arrivals and completions, as well as on
4049  * idle timer expirations.
4050  */
4051 static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
4052 {
4053         return time_is_before_eq_jiffies(bfqq->budget_timeout);
4054 }
4055 
4056 /*
4057  * If we expire a queue that is actively waiting (i.e., with the
4058  * device idled) for the arrival of a new request, then we may incur
4059  * the timestamp misalignment problem described in the body of the
4060  * function __bfq_activate_entity. Hence we return true only if this
4061  * condition does not hold, or if the queue is slow enough to deserve
4062  * only to be kicked off for preserving a high throughput.
4063  */
4064 static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
4065 {
4066         bfq_log_bfqq(bfqq->bfqd, bfqq,
4067                 "may_budget_timeout: wait_request %d left %d timeout %d",
4068                 bfq_bfqq_wait_request(bfqq),
4069                         bfq_bfqq_budget_left(bfqq) >=  bfqq->entity.budget / 3,
4070                 bfq_bfqq_budget_timeout(bfqq));
4071 
4072         return (!bfq_bfqq_wait_request(bfqq) ||
4073                 bfq_bfqq_budget_left(bfqq) >=  bfqq->entity.budget / 3)
4074                 &&
4075                 bfq_bfqq_budget_timeout(bfqq);
4076 }
4077 
4078 static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
4079                                              struct bfq_queue *bfqq)
4080 {
4081         bool rot_without_queueing =
4082                 !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag,
4083                 bfqq_sequential_and_IO_bound,
4084                 idling_boosts_thr;
4085 
4086         /* No point in idling for bfqq if it won't get requests any longer */
4087         if (unlikely(!bfqq_process_refs(bfqq)))
4088                 return false;
4089 
4090         bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
4091                 bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);
4092 
4093         /*
4094          * The next variable takes into account the cases where idling
4095          * boosts the throughput.
4096          *
4097          * The value of the variable is computed considering, first, that
4098          * idling is virtually always beneficial for the throughput if:
4099          * (a) the device is not NCQ-capable and rotational, or
4100          * (b) regardless of the presence of NCQ, the device is rotational and
4101          *     the request pattern for bfqq is I/O-bound and sequential, or
4102          * (c) regardless of whether it is rotational, the device is
4103          *     not NCQ-capable and the request pattern for bfqq is
4104          *     I/O-bound and sequential.
4105          *
4106          * Secondly, and in contrast to the above item (b), idling an
4107          * NCQ-capable flash-based device would not boost the
4108          * throughput even with sequential I/O; rather it would lower
4109          * the throughput in proportion to how fast the device
4110          * is. Accordingly, the next variable is true if any of the
4111          * above conditions (a), (b) or (c) is true, and, in
4112          * particular, happens to be false if bfqd is an NCQ-capable
4113          * flash-based device.
4114          */
4115         idling_boosts_thr = rot_without_queueing ||
4116                 ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) &&
4117                  bfqq_sequential_and_IO_bound);
4118 
4119         /*
4120          * The return value of this function is equal to that of
4121          * idling_boosts_thr, unless a special case holds. In this
4122          * special case, described below, idling may cause problems to
4123          * weight-raised queues.
4124          *
4125          * When the request pool is saturated (e.g., in the presence
4126          * of write hogs), if the processes associated with
4127          * non-weight-raised queues ask for requests at a lower rate,
4128          * then processes associated with weight-raised queues have a
4129          * higher probability to get a request from the pool
4130          * immediately (or at least soon) when they need one. Thus
4131          * they have a higher probability to actually get a fraction
4132          * of the device throughput proportional to their high
4133          * weight. This is especially true with NCQ-capable drives,
4134          * which enqueue several requests in advance, and further
4135          * reorder internally-queued requests.
4136          *
4137          * For this reason, we force to false the return value if
4138          * there are weight-raised busy queues. In this case, and if
4139          * bfqq is not weight-raised, this guarantees that the device
4140          * is not idled for bfqq (if, instead, bfqq is weight-raised,
4141          * then idling will be guaranteed by another variable, see
4142          * below). Combined with the timestamping rules of BFQ (see
4143          * [1] for details), this behavior causes bfqq, and hence any
4144          * sync non-weight-raised queue, to get a lower number of
4145          * requests served, and thus to ask for a lower number of
4146          * requests from the request pool, before the busy
4147          * weight-raised queues get served again. This often mitigates
4148          * starvation problems in the presence of heavy write
4149          * workloads and NCQ, thereby guaranteeing a higher
4150          * application and system responsiveness in these hostile
4151          * scenarios.
4152          */
4153         return idling_boosts_thr &&
4154                 bfqd->wr_busy_queues == 0;
4155 }
4156 
4157 /*
4158  * For a queue that becomes empty, device idling is allowed only if
4159  * this function returns true for that queue. As a consequence, since
4160  * device idling plays a critical role for both throughput boosting
4161  * and service guarantees, the return value of this function plays a
4162  * critical role as well.
4163  *
4164  * In a nutshell, this function returns true only if idling is
4165  * beneficial for throughput or, even if detrimental for throughput,
4166  * idling is however necessary to preserve service guarantees (low
4167  * latency, desired throughput distribution, ...). In particular, on
4168  * NCQ-capable devices, this function tries to return false, so as to
4169  * help keep the drives' internal queues full, whenever this helps the
4170  * device boost the throughput without causing any service-guarantee
4171  * issue.
4172  *
4173  * Most of the issues taken into account to get the return value of
4174  * this function are not trivial. We discuss these issues in the two
4175  * functions providing the main pieces of information needed by this
4176  * function.
4177  */
4178 static bool bfq_better_to_idle(struct bfq_queue *bfqq)
4179 {
4180         struct bfq_data *bfqd = bfqq->bfqd;
4181         bool idling_boosts_thr_with_no_issue, idling_needed_for_service_guar;
4182 
4183         /* No point in idling for bfqq if it won't get requests any longer */
4184         if (unlikely(!bfqq_process_refs(bfqq)))
4185                 return false;
4186 
4187         if (unlikely(bfqd->strict_guarantees))
4188                 return true;
4189 
4190         /*
4191          * Idling is performed only if slice_idle > 0. In addition, we
4192          * do not idle if
4193          * (a) bfqq is async
4194          * (b) bfqq is in the idle io prio class: in this case we do
4195          * not idle because we want to minimize the bandwidth that
4196          * queues in this class can steal to higher-priority queues
4197          */
4198         if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
4199            bfq_class_idle(bfqq))
4200                 return false;
4201 
4202         idling_boosts_thr_with_no_issue =
4203                 idling_boosts_thr_without_issues(bfqd, bfqq);
4204 
4205         idling_needed_for_service_guar =
4206                 idling_needed_for_service_guarantees(bfqd, bfqq);
4207 
4208         /*
4209          * We have now the two components we need to compute the
4210          * return value of the function, which is true only if idling
4211          * either boosts the throughput (without issues), or is
4212          * necessary to preserve service guarantees.
4213          */
4214         return idling_boosts_thr_with_no_issue ||
4215                 idling_needed_for_service_guar;
4216 }
4217 
4218 /*
4219  * If the in-service queue is empty but the function bfq_better_to_idle
4220  * returns true, then:
4221  * 1) the queue must remain in service and cannot be expired, and
4222  * 2) the device must be idled to wait for the possible arrival of a new
4223  *    request for the queue.
4224  * See the comments on the function bfq_better_to_idle for the reasons
4225  * why performing device idling is the best choice to boost the throughput
4226  * and preserve service guarantees when bfq_better_to_idle itself
4227  * returns true.
4228  */
4229 static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
4230 {
4231         return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq);
4232 }
4233 
4234 /*
4235  * This function chooses the queue from which to pick the next extra
4236  * I/O request to inject, if it finds a compatible queue. See the
4237  * comments on bfq_update_inject_limit() for details on the injection
4238  * mechanism, and for the definitions of the quantities mentioned
4239  * below.
4240  */
4241 static struct bfq_queue *
4242 bfq_choose_bfqq_for_injection(struct bfq_data *bfqd)
4243 {
4244         struct bfq_queue *bfqq, *in_serv_bfqq = bfqd->in_service_queue;
4245         unsigned int limit = in_serv_bfqq->inject_limit;
4246         /*
4247          * If
4248          * - bfqq is not weight-raised and therefore does not carry
4249          *   time-critical I/O,
4250          * or
4251          * - regardless of whether bfqq is weight-raised, bfqq has
4252          *   however a long think time, during which it can absorb the
4253          *   effect of an appropriate number of extra I/O requests
4254          *   from other queues (see bfq_update_inject_limit for
4255          *   details on the computation of this number);
4256          * then injection can be performed without restrictions.
4257          */
4258         bool in_serv_always_inject = in_serv_bfqq->wr_coeff == 1 ||
4259                 !bfq_bfqq_has_short_ttime(in_serv_bfqq);
4260 
4261         /*
4262          * If
4263          * - the baseline total service time could not be sampled yet,
4264          *   so the inject limit happens to be still 0, and
4265          * - a lot of time has elapsed since the plugging of I/O
4266          *   dispatching started, so drive speed is being wasted
4267          *   significantly;
4268          * then temporarily raise inject limit to one request.
4269          */
4270         if (limit == 0 && in_serv_bfqq->last_serv_time_ns == 0 &&
4271             bfq_bfqq_wait_request(in_serv_bfqq) &&
4272             time_is_before_eq_jiffies(bfqd->last_idling_start_jiffies +
4273                                       bfqd->bfq_slice_idle)
4274                 )
4275                 limit = 1;
4276 
4277         if (bfqd->rq_in_driver >= limit)
4278                 return NULL;
4279 
4280         /*
4281          * Linear search of the source queue for injection; but, with
4282          * a high probability, very few steps are needed to find a
4283          * candidate queue, i.e., a queue with enough budget left for
4284          * its next request. In fact:
4285          * - BFQ dynamically updates the budget of every queue so as
4286          *   to accommodate the expected backlog of the queue;
4287          * - if a queue gets all its requests dispatched as injected
4288          *   service, then the queue is removed from the active list
4289          *   (and re-added only if it gets new requests, but then it
4290          *   is assigned again enough budget for its new backlog).
4291          */
4292         list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
4293                 if (!RB_EMPTY_ROOT(&bfqq->sort_list) &&
4294                     (in_serv_always_inject || bfqq->wr_coeff > 1) &&
4295                     bfq_serv_to_charge(bfqq->next_rq, bfqq) <=
4296                     bfq_bfqq_budget_left(bfqq)) {
4297                         /*
4298                          * Allow for only one large in-flight request
4299                          * on non-rotational devices, for the
4300                          * following reason. On non-rotationl drives,
4301                          * large requests take much longer than
4302                          * smaller requests to be served. In addition,
4303                          * the drive prefers to serve large requests
4304                          * w.r.t. to small ones, if it can choose. So,
4305                          * having more than one large requests queued
4306                          * in the drive may easily make the next first
4307                          * request of the in-service queue wait for so
4308                          * long to break bfqq's service guarantees. On
4309                          * the bright side, large requests let the
4310                          * drive reach a very high throughput, even if
4311                          * there is only one in-flight large request
4312                          * at a time.
4313                          */
4314                         if (blk_queue_nonrot(bfqd->queue) &&
4315                             blk_rq_sectors(bfqq->next_rq) >=
4316                             BFQQ_SECT_THR_NONROT)
4317                                 limit = min_t(unsigned int, 1, limit);
4318                         else
4319                                 limit = in_serv_bfqq->inject_limit;
4320 
4321                         if (bfqd->rq_in_driver < limit) {
4322                                 bfqd->rqs_injected = true;
4323                                 return bfqq;
4324                         }
4325                 }
4326 
4327         return NULL;
4328 }
4329 
4330 /*
4331  * Select a queue for service.  If we have a current queue in service,
4332  * check whether to continue servicing it, or retrieve and set a new one.
4333  */
4334 static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
4335 {
4336         struct bfq_queue *bfqq;
4337         struct request *next_rq;
4338         enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
4339 
4340         bfqq = bfqd->in_service_queue;
4341         if (!bfqq)
4342                 goto new_queue;
4343 
4344         bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
4345 
4346         /*
4347          * Do not expire bfqq for budget timeout if bfqq may be about
4348          * to enjoy device idling. The reason why, in this case, we
4349          * prevent bfqq from expiring is the same as in the comments
4350          * on the case where bfq_bfqq_must_idle() returns true, in
4351          * bfq_completed_request().
4352          */
4353         if (bfq_may_expire_for_budg_timeout(bfqq) &&
4354             !bfq_bfqq_must_idle(bfqq))
4355                 goto expire;
4356 
4357 check_queue:
4358         /*
4359          * This loop is rarely executed more than once. Even when it
4360          * happens, it is much more convenient to re-execute this loop
4361          * than to return NULL and trigger a new dispatch to get a
4362          * request served.
4363          */
4364         next_rq = bfqq->next_rq;
4365         /*
4366          * If bfqq has requests queued and it has enough budget left to
4367          * serve them, keep the queue, otherwise expire it.
4368          */
4369         if (next_rq) {
4370                 if (bfq_serv_to_charge(next_rq, bfqq) >
4371                         bfq_bfqq_budget_left(bfqq)) {
4372                         /*
4373                          * Expire the queue for budget exhaustion,
4374                          * which makes sure that the next budget is
4375                          * enough to serve the next request, even if
4376                          * it comes from the fifo expired path.
4377                          */
4378                         reason = BFQQE_BUDGET_EXHAUSTED;
4379                         goto expire;
4380                 } else {
4381                         /*
4382                          * The idle timer may be pending because we may
4383                          * not disable disk idling even when a new request
4384                          * arrives.
4385                          */
4386                         if (bfq_bfqq_wait_request(bfqq)) {
4387                                 /*
4388                                  * If we get here: 1) at least a new request
4389                                  * has arrived but we have not disabled the
4390                                  * timer because the request was too small,
4391                                  * 2) then the block layer has unplugged
4392                                  * the device, causing the dispatch to be
4393                                  * invoked.
4394                                  *
4395                                  * Since the device is unplugged, now the
4396                                  * requests are probably large enough to
4397                                  * provide a reasonable throughput.
4398                                  * So we disable idling.
4399                                  */
4400                                 bfq_clear_bfqq_wait_request(bfqq);
4401                                 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
4402                         }
4403                         goto keep_queue;
4404                 }
4405         }
4406 
4407         /*
4408          * No requests pending. However, if the in-service queue is idling
4409          * for a new request, or has requests waiting for a completion and
4410          * may idle after their completion, then keep it anyway.
4411          *
4412          * Yet, inject service from other queues if it boosts
4413          * throughput and is possible.
4414          */
4415         if (bfq_bfqq_wait_request(bfqq) ||
4416             (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) {
4417                 struct bfq_queue *async_bfqq =
4418                         bfqq->bic && bfqq->bic->bfqq[0] &&
4419                         bfq_bfqq_busy(bfqq->bic->bfqq[0]) &&
4420                         bfqq->bic->bfqq[0]->next_rq ?
4421                         bfqq->bic->bfqq[0] : NULL;
4422 
4423                 /*
4424                  * The next three mutually-exclusive ifs decide
4425                  * whether to try injection, and choose the queue to
4426                  * pick an I/O request from.
4427                  *
4428                  * The first if checks whether the process associated
4429                  * with bfqq has also async I/O pending. If so, it
4430                  * injects such I/O unconditionally. Injecting async
4431                  * I/O from the same process can cause no harm to the
4432                  * process. On the contrary, it can only increase
4433                  * bandwidth and reduce latency for the process.
4434                  *
4435                  * The second if checks whether there happens to be a
4436                  * non-empty waker queue for bfqq, i.e., a queue whose
4437                  * I/O needs to be completed for bfqq to receive new
4438                  * I/O. This happens, e.g., if bfqq is associated with
4439                  * a process that does some sync. A sync generates
4440                  * extra blocking I/O, which must be completed before
4441                  * the process associated with bfqq can go on with its
4442                  * I/O. If the I/O of the waker queue is not served,
4443                  * then bfqq remains empty, and no I/O is dispatched,
4444                  * until the idle timeout fires for bfqq. This is
4445                  * likely to result in lower bandwidth and higher
4446                  * latencies for bfqq, and in a severe loss of total
4447                  * throughput. The best action to take is therefore to
4448                  * serve the waker queue as soon as possible. So do it
4449                  * (without relying on the third alternative below for
4450                  * eventually serving waker_bfqq's I/O; see the last
4451                  * paragraph for further details). This systematic
4452                  * injection of I/O from the waker queue does not
4453                  * cause any delay to bfqq's I/O. On the contrary,
4454                  * next bfqq's I/O is brought forward dramatically,
4455                  * for it is not blocked for milliseconds.
4456                  *
4457                  * The third if checks whether bfqq is a queue for
4458                  * which it is better to avoid injection. It is so if
4459                  * bfqq delivers more throughput when served without
4460                  * any further I/O from other queues in the middle, or
4461                  * if the service times of bfqq's I/O requests both
4462                  * count more than overall throughput, and may be
4463                  * easily increased by injection (this happens if bfqq
4464                  * has a short think time). If none of these
4465                  * conditions holds, then a candidate queue for
4466                  * injection is looked for through
4467                  * bfq_choose_bfqq_for_injection(). Note that the
4468                  * latter may return NULL (for example if the inject
4469                  * limit for bfqq is currently 0).
4470                  *
4471                  * NOTE: motivation for the second alternative
4472                  *
4473                  * Thanks to the way the inject limit is updated in
4474                  * bfq_update_has_short_ttime(), it is rather likely
4475                  * that, if I/O is being plugged for bfqq and the
4476                  * waker queue has pending I/O requests that are
4477                  * blocking bfqq's I/O, then the third alternative
4478                  * above lets the waker queue get served before the
4479                  * I/O-plugging timeout fires. So one may deem the
4480                  * second alternative superfluous. It is not, because
4481                  * the third alternative may be way less effective in
4482                  * case of a synchronization. For two main
4483                  * reasons. First, throughput may be low because the
4484                  * inject limit may be too low to guarantee the same
4485                  * amount of injected I/O, from the waker queue or
4486                  * other queues, that the second alternative
4487                  * guarantees (the second alternative unconditionally
4488                  * injects a pending I/O request of the waker queue
4489                  * for each bfq_dispatch_request()). Second, with the
4490                  * third alternative, the duration of the plugging,
4491                  * i.e., the time before bfqq finally receives new I/O,
4492                  * may not be minimized, because the waker queue may
4493                  * happen to be served only after other queues.
4494                  */
4495                 if (async_bfqq &&
4496                     icq_to_bic(async_bfqq->next_rq->elv.icq) == bfqq->bic &&
4497                     bfq_serv_to_charge(async_bfqq->next_rq, async_bfqq) <=
4498                     bfq_bfqq_budget_left(async_bfqq))
4499                         bfqq = bfqq->bic->bfqq[0];
4500                 else if (bfq_bfqq_has_waker(bfqq) &&
4501                            bfq_bfqq_busy(bfqq->waker_bfqq) &&
4502                            bfqq->next_rq &&
4503                            bfq_serv_to_charge(bfqq->waker_bfqq->next_rq,
4504                                               bfqq->waker_bfqq) <=
4505                            bfq_bfqq_budget_left(bfqq->waker_bfqq)
4506                         )
4507                         bfqq = bfqq->waker_bfqq;
4508                 else if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
4509                          (bfqq->wr_coeff == 1 || bfqd->wr_busy_queues > 1 ||
4510                           !bfq_bfqq_has_short_ttime(bfqq)))
4511                         bfqq = bfq_choose_bfqq_for_injection(bfqd);
4512                 else
4513                         bfqq = NULL;
4514 
4515                 goto keep_queue;
4516         }
4517 
4518         reason = BFQQE_NO_MORE_REQUESTS;
4519 expire:
4520         bfq_bfqq_expire(bfqd, bfqq, false, reason);
4521 new_queue:
4522         bfqq = bfq_set_in_service_queue(bfqd);
4523         if (bfqq) {
4524                 bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
4525                 goto check_queue;
4526         }
4527 keep_queue:
4528         if (bfqq)
4529                 bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
4530         else
4531                 bfq_log(bfqd, "select_queue: no queue returned");
4532 
4533         return bfqq;
4534 }
4535 
4536 static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
4537 {
4538         struct bfq_entity *entity = &bfqq->entity;
4539 
4540         if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
4541                 bfq_log_bfqq(bfqd, bfqq,
4542                         "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
4543                         jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
4544                         jiffies_to_msecs(bfqq->wr_cur_max_time),
4545                         bfqq->wr_coeff,
4546                         bfqq->entity.weight, bfqq->entity.orig_weight);
4547 
4548                 if (entity->prio_changed)
4549                         bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
4550 
4551                 /*
4552                  * If the queue was activated in a burst, or too much
4553                  * time has elapsed from the beginning of this
4554                  * weight-raising period, then end weight raising.
4555                  */
4556                 if (bfq_bfqq_in_large_burst(bfqq))
4557                         bfq_bfqq_end_wr(bfqq);
4558                 else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
4559                                                 bfqq->wr_cur_max_time)) {
4560                         if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
4561                         time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
4562                                                bfq_wr_duration(bfqd)))
4563                                 bfq_bfqq_end_wr(bfqq);
4564                         else {
4565                                 switch_back_to_interactive_wr(bfqq, bfqd);
4566                                 bfqq->entity.prio_changed = 1;
4567                         }
4568                 }
4569                 if (bfqq->wr_coeff > 1 &&
4570                     bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time &&
4571                     bfqq->service_from_wr > max_service_from_wr) {
4572                         /* see comments on max_service_from_wr */
4573                         bfq_bfqq_end_wr(bfqq);
4574                 }
4575         }
4576         /*
4577          * To improve latency (for this or other queues), immediately
4578          * update weight both if it must be raised and if it must be
4579          * lowered. Since, entity may be on some active tree here, and
4580          * might have a pending change of its ioprio class, invoke
4581          * next function with the last parameter unset (see the
4582          * comments on the function).
4583          */
4584         if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
4585                 __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
4586                                                 entity, false);
4587 }
4588 
4589 /*
4590  * Dispatch next request from bfqq.
4591  */
4592 static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
4593                                                  struct bfq_queue *bfqq)
4594 {
4595         struct request *rq = bfqq->next_rq;
4596         unsigned long service_to_charge;
4597 
4598         service_to_charge = bfq_serv_to_charge(rq, bfqq);
4599 
4600         bfq_bfqq_served(bfqq, service_to_charge);
4601 
4602         if (bfqq == bfqd->in_service_queue && bfqd->wait_dispatch) {
4603                 bfqd->wait_dispatch = false;
4604                 bfqd->waited_rq = rq;
4605         }
4606 
4607         bfq_dispatch_remove(bfqd->queue, rq);
4608 
4609         if (bfqq != bfqd->in_service_queue)
4610                 goto return_rq;
4611 
4612         /*
4613          * If weight raising has to terminate for bfqq, then next
4614          * function causes an immediate update of bfqq's weight,
4615          * without waiting for next activation. As a consequence, on
4616          * expiration, bfqq will be timestamped as if has never been
4617          * weight-raised during this service slot, even if it has
4618          * received part or even most of the service as a
4619          * weight-raised queue. This inflates bfqq's timestamps, which
4620          * is beneficial, as bfqq is then more willing to leave the
4621          * device immediately to possible other weight-raised queues.
4622          */
4623         bfq_update_wr_data(bfqd, bfqq);
4624 
4625         /*
4626          * Expire bfqq, pretending that its budget expired, if bfqq
4627          * belongs to CLASS_IDLE and other queues are waiting for
4628          * service.
4629          */
4630         if (!(bfq_tot_busy_queues(bfqd) > 1 && bfq_class_idle(bfqq)))
4631                 goto return_rq;
4632 
4633         bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
4634 
4635 return_rq:
4636         return rq;
4637 }
4638 
4639 static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
4640 {
4641         struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
4642 
4643         /*
4644          * Avoiding lock: a race on bfqd->busy_queues should cause at
4645          * most a call to dispatch for nothing
4646          */
4647         return !list_empty_careful(&bfqd->dispatch) ||
4648                 bfq_tot_busy_queues(bfqd) > 0;
4649 }
4650 
4651 static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
4652 {
4653         struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
4654         struct request *rq = NULL;
4655         struct bfq_queue *bfqq = NULL;
4656 
4657         if (!list_empty(&bfqd->dispatch)) {
4658                 rq = list_first_entry(&bfqd->dispatch, struct request,
4659                                       queuelist);
4660                 list_del_init(&rq->queuelist);
4661 
4662                 bfqq = RQ_BFQQ(rq);
4663 
4664                 if (bfqq) {
4665                         /*
4666                          * Increment counters here, because this
4667                          * dispatch does not follow the standard
4668                          * dispatch flow (where counters are
4669                          * incremented)
4670                          */
4671                         bfqq->dispatched++;
4672 
4673                         goto inc_in_driver_start_rq;
4674                 }
4675 
4676                 /*
4677                  * We exploit the bfq_finish_requeue_request hook to
4678                  * decrement rq_in_driver, but
4679                  * bfq_finish_requeue_request will not be invoked on
4680                  * this request. So, to avoid unbalance, just start
4681                  * this request, without incrementing rq_in_driver. As
4682                  * a negative consequence, rq_in_driver is deceptively
4683                  * lower than it should be while this request is in
4684                  * service. This may cause bfq_schedule_dispatch to be
4685                  * invoked uselessly.
4686                  *
4687                  * As for implementing an exact solution, the
4688                  * bfq_finish_requeue_request hook, if defined, is
4689                  * probably invoked also on this request. So, by
4690                  * exploiting this hook, we could 1) increment
4691                  * rq_in_driver here, and 2) decrement it in
4692                  * bfq_finish_requeue_request. Such a solution would
4693                  * let the value of the counter be always accurate,
4694                  * but it would entail using an extra interface
4695                  * function. This cost seems higher than the benefit,
4696                  * being the frequency of non-elevator-private
4697                  * requests very low.
4698                  */
4699                 goto start_rq;
4700         }
4701 
4702         bfq_log(bfqd, "dispatch requests: %d busy queues",
4703                 bfq_tot_busy_queues(bfqd));
4704 
4705         if (bfq_tot_busy_queues(bfqd) == 0)
4706                 goto exit;
4707 
4708         /*
4709          * Force device to serve one request at a time if
4710          * strict_guarantees is true. Forcing this service scheme is
4711          * currently the ONLY way to guarantee that the request
4712          * service order enforced by the scheduler is respected by a
4713          * queueing device. Otherwise the device is free even to make
4714          * some unlucky request wait for as long as the device
4715          * wishes.
4716          *
4717          * Of course, serving one request at at time may cause loss of
4718          * throughput.
4719          */
4720         if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
4721                 goto exit;
4722 
4723         bfqq = bfq_select_queue(bfqd);
4724         if (!bfqq)
4725                 goto exit;
4726 
4727         rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
4728 
4729         if (rq) {
4730 inc_in_driver_start_rq:
4731                 bfqd->rq_in_driver++;
4732 start_rq:
4733                 rq->rq_flags |= RQF_STARTED;
4734         }
4735 exit:
4736         return rq;
4737 }
4738 
4739 #ifdef CONFIG_BFQ_CGROUP_DEBUG
4740 static void bfq_update_dispatch_stats(struct request_queue *q,
4741                                       struct request *rq,
4742                                       struct bfq_queue *in_serv_queue,
4743                                       bool idle_timer_disabled)
4744 {
4745         struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL;
4746 
4747         if (!idle_timer_disabled && !bfqq)
4748                 return;
4749 
4750         /*
4751          * rq and bfqq are guaranteed to exist until this function
4752          * ends, for the following reasons. First, rq can be
4753          * dispatched to the device, and then can be completed and
4754          * freed, only after this function ends. Second, rq cannot be
4755          * merged (and thus freed because of a merge) any longer,
4756          * because it has already started. Thus rq cannot be freed
4757          * before this function ends, and, since rq has a reference to
4758          * bfqq, the same guarantee holds for bfqq too.
4759          *
4760          * In addition, the following queue lock guarantees that
4761          * bfqq_group(bfqq) exists as well.
4762          */
4763         spin_lock_irq(&q->queue_lock);
4764         if (idle_timer_disabled)
4765                 /*
4766                  * Since the idle timer has been disabled,
4767                  * in_serv_queue contained some request when
4768                  * __bfq_dispatch_request was invoked above, which
4769                  * implies that rq was picked exactly from
4770                  * in_serv_queue. Thus in_serv_queue == bfqq, and is
4771                  * therefore guaranteed to exist because of the above
4772                  * arguments.
4773                  */
4774                 bfqg_stats_update_idle_time(bfqq_group(in_serv_queue));
4775         if (bfqq) {
4776                 struct bfq_group *bfqg = bfqq_group(bfqq);
4777 
4778                 bfqg_stats_update_avg_queue_size(bfqg);
4779                 bfqg_stats_set_start_empty_time(bfqg);
4780                 bfqg_stats_update_io_remove(bfqg, rq->cmd_flags);
4781         }
4782         spin_unlock_irq(&q->queue_lock);
4783 }
4784 #else
4785 static inline void bfq_update_dispatch_stats(struct request_queue *q,
4786                                              struct request *rq,
4787                                              struct bfq_queue *in_serv_queue,
4788                                              bool idle_timer_disabled) {}
4789 #endif /* CONFIG_BFQ_CGROUP_DEBUG */
4790 
4791 static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
4792 {
4793         struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
4794         struct request *rq;
4795         struct bfq_queue *in_serv_queue;
4796         bool waiting_rq, idle_timer_disabled;
4797 
4798         spin_lock_irq(&bfqd->lock);
4799 
4800         in_serv_queue = bfqd->in_service_queue;
4801         waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);
4802 
4803         rq = __bfq_dispatch_request(hctx);
4804 
4805         idle_timer_disabled =
4806                 waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
4807 
4808         spin_unlock_irq(&bfqd->lock);
4809 
4810         bfq_update_dispatch_stats(hctx->queue, rq, in_serv_queue,
4811                                   idle_timer_disabled);
4812 
4813         return rq;
4814 }
4815 
4816 /*
4817  * Task holds one reference to the queue, dropped when task exits.  Each rq
4818  * in-flight on this queue also holds a reference, dropped when rq is freed.
4819  *
4820  * Scheduler lock must be held here. Recall not to use bfqq after calling
4821  * this function on it.
4822  */
4823 void bfq_put_queue(struct bfq_queue *bfqq)
4824 {
4825         struct bfq_queue *item;
4826         struct hlist_node *n;
4827         struct bfq_group *bfqg = bfqq_group(bfqq);
4828 
4829         if (bfqq->bfqd)
4830                 bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d",
4831                              bfqq, bfqq->ref);
4832 
4833         bfqq->ref--;
4834         if (bfqq->ref)
4835                 return;
4836 
4837         if (!hlist_unhashed(&bfqq->burst_list_node)) {
4838                 hlist_del_init(&bfqq->burst_list_node);
4839                 /*
4840                  * Decrement also burst size after the removal, if the
4841                  * process associated with bfqq is exiting, and thus
4842                  * does not contribute to the burst any longer. This
4843                  * decrement helps filter out false positives of large
4844                  * bursts, when some short-lived process (often due to
4845                  * the execution of commands by some service) happens
4846                  * to start and exit while a complex application is
4847                  * starting, and thus spawning several processes that
4848                  * do I/O (and that *must not* be treated as a large
4849                  * burst, see comments on bfq_handle_burst).
4850                  *
4851                  * In particular, the decrement is performed only if:
4852                  * 1) bfqq is not a merged queue, because, if it is,
4853                  * then this free of bfqq is not triggered by the exit
4854                  * of the process bfqq is associated with, but exactly
4855                  * by the fact that bfqq has just been merged.
4856                  * 2) burst_size is greater than 0, to handle
4857                  * unbalanced decrements. Unbalanced decrements may
4858                  * happen in te following case: bfqq is inserted into
4859                  * the current burst list--without incrementing
4860                  * bust_size--because of a split, but the current
4861                  * burst list is not the burst list bfqq belonged to
4862                  * (see comments on the case of a split in
4863                  * bfq_set_request).
4864                  */
4865                 if (bfqq->bic && bfqq->bfqd->burst_size > 0)
4866                         bfqq->bfqd->burst_size--;
4867         }
4868 
4869         /*
4870          * bfqq does not exist any longer, so it cannot be woken by
4871          * any other queue, and cannot wake any other queue. Then bfqq
4872          * must be removed from the woken list of its possible waker
4873          * queue, and all queues in the woken list of bfqq must stop
4874          * having a waker queue. Strictly speaking, these updates
4875          * should be performed when bfqq remains with no I/O source
4876          * attached to it, which happens before bfqq gets freed. In
4877          * particular, this happens when the last process associated
4878          * with bfqq exits or gets associated with a different
4879          * queue. However, both events lead to bfqq being freed soon,
4880          * and dangling references would come out only after bfqq gets
4881          * freed. So these updates are done here, as a simple and safe
4882          * way to handle all cases.
4883          */
4884         /* remove bfqq from woken list */
4885         if (!hlist_unhashed(&bfqq->woken_list_node))
4886                 hlist_del_init(&bfqq->woken_list_node);
4887 
4888         /* reset waker for all queues in woken list */
4889         hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
4890                                   woken_list_node) {
4891                 item->waker_bfqq = NULL;
4892                 bfq_clear_bfqq_has_waker(item);
4893                 hlist_del_init(&item->woken_list_node);
4894         }
4895 
4896         if (bfqq->bfqd && bfqq->bfqd->last_completed_rq_bfqq == bfqq)
4897                 bfqq->bfqd->last_completed_rq_bfqq = NULL;
4898 
4899         kmem_cache_free(bfq_pool, bfqq);
4900         bfqg_and_blkg_put(bfqg);
4901 }
4902 
4903 static void bfq_put_cooperator(struct bfq_queue *bfqq)
4904 {
4905         struct bfq_queue *__bfqq, *next;
4906 
4907         /*
4908          * If this queue was scheduled to merge with another queue, be
4909          * sure to drop the reference taken on that queue (and others in
4910          * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
4911          */
4912         __bfqq = bfqq->new_bfqq;
4913         while (__bfqq) {
4914                 if (__bfqq == bfqq)
4915                         break;
4916                 next = __bfqq->new_bfqq;
4917                 bfq_put_queue(__bfqq);
4918                 __bfqq = next;
4919         }
4920 }
4921 
4922 static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
4923 {
4924         if (bfqq == bfqd->in_service_queue) {
4925                 __bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT);
4926                 bfq_schedule_dispatch(bfqd);
4927         }
4928 
4929         bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
4930 
4931         bfq_put_cooperator(bfqq);
4932 
4933         bfq_release_process_ref(bfqd, bfqq);
4934 }
4935 
4936 static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
4937 {
4938         struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
4939         struct bfq_data *bfqd;
4940 
4941         if (bfqq)
4942                 bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
4943 
4944         if (bfqq && bfqd) {
4945                 unsigned long flags;
4946 
4947                 spin_lock_irqsave(&bfqd->lock, flags);
4948                 bfqq->bic = NULL;
4949                 bfq_exit_bfqq(bfqd, bfqq);
4950                 bic_set_bfqq(bic, NULL, is_sync);
4951                 spin_unlock_irqrestore(&bfqd->lock, flags);
4952         }
4953 }
4954 
4955 static void bfq_exit_icq(struct io_cq *icq)
4956 {
4957         struct bfq_io_cq *bic = icq_to_bic(icq);
4958 
4959         bfq_exit_icq_bfqq(bic, true);
4960         bfq_exit_icq_bfqq(bic, false);
4961 }
4962 
4963 /*
4964  * Update the entity prio values; note that the new values will not
4965  * be used until the next (re)activation.
4966  */
4967 static void
4968 bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
4969 {
4970         struct task_struct *tsk = current;
4971         int ioprio_class;
4972         struct bfq_data *bfqd = bfqq->bfqd;
4973 
4974         if (!bfqd)
4975                 return;
4976 
4977         ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
4978         switch (ioprio_class) {
4979         default:
4980                 pr_err("bdi %s: bfq: bad prio class %d\n",
4981                                 bdi_dev_name(bfqq->bfqd->queue->backing_dev_info),
4982                                 ioprio_class);
4983                 /* fall through */
4984         case IOPRIO_CLASS_NONE:
4985                 /*
4986                  * No prio set, inherit CPU scheduling settings.
4987                  */
4988                 bfqq->new_ioprio = task_nice_ioprio(tsk);
4989                 bfqq->new_ioprio_class = task_nice_ioclass(tsk);
4990                 break;
4991         case IOPRIO_CLASS_RT:
4992                 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
4993                 bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
4994                 break;
4995         case IOPRIO_CLASS_BE:
4996                 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
4997                 bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
4998                 break;
4999         case IOPRIO_CLASS_IDLE:
5000                 bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
5001                 bfqq->new_ioprio = 7;
5002                 break;
5003         }
5004 
5005         if (bfqq->new_ioprio >= IOPRIO_BE_NR) {
5006                 pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
5007                         bfqq->new_ioprio);
5008                 bfqq->new_ioprio = IOPRIO_BE_NR;
5009         }
5010 
5011         bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
5012         bfqq->entity.prio_changed = 1;
5013 }
5014 
5015 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5016                                        struct bio *bio, bool is_sync,
5017                                        struct bfq_io_cq *bic);
5018 
5019 static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
5020 {
5021         struct bfq_data *bfqd = bic_to_bfqd(bic);
5022         struct bfq_queue *bfqq;
5023         int ioprio = bic->icq.ioc->ioprio;
5024 
5025         /*
5026          * This condition may trigger on a newly created bic, be sure to
5027          * drop the lock before returning.
5028          */
5029         if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
5030                 return;
5031 
5032         bic->ioprio = ioprio;
5033 
5034         bfqq = bic_to_bfqq(bic, false);
5035         if (bfqq) {
5036                 bfq_release_process_ref(bfqd, bfqq);
5037                 bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic);
5038                 bic_set_bfqq(bic, bfqq, false);
5039         }
5040 
5041         bfqq = bic_to_bfqq(bic, true);
5042         if (bfqq)
5043                 bfq_set_next_ioprio_data(bfqq, bic);
5044 }
5045 
5046 static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5047                           struct bfq_io_cq *bic, pid_t pid, int is_sync)
5048 {
5049         RB_CLEAR_NODE(&bfqq->entity.rb_node);
5050         INIT_LIST_HEAD(&bfqq->fifo);
5051         INIT_HLIST_NODE(&bfqq->burst_list_node);
5052         INIT_HLIST_NODE(&bfqq->woken_list_node);
5053         INIT_HLIST_HEAD(&bfqq->woken_list);
5054 
5055         bfqq->ref = 0;
5056         bfqq->bfqd = bfqd;
5057 
5058         if (bic)
5059                 bfq_set_next_ioprio_data(bfqq, bic);
5060 
5061         if (is_sync) {
5062                 /*
5063                  * No need to mark as has_short_ttime if in
5064                  * idle_class, because no device idling is performed
5065                  * for queues in idle class
5066                  */
5067                 if (!bfq_class_idle(bfqq))
5068                         /* tentatively mark as has_short_ttime */
5069                         bfq_mark_bfqq_has_short_ttime(bfqq);
5070                 bfq_mark_bfqq_sync(bfqq);
5071                 bfq_mark_bfqq_just_created(bfqq);
5072         } else
5073                 bfq_clear_bfqq_sync(bfqq);
5074 
5075         /* set end request to minus infinity from now */
5076         bfqq->ttime.last_end_request = ktime_get_ns() + 1;
5077 
5078         bfq_mark_bfqq_IO_bound(bfqq);
5079 
5080         bfqq->pid = pid;
5081 
5082         /* Tentative initial value to trade off between thr and lat */
5083         bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
5084         bfqq->budget_timeout = bfq_smallest_from_now();
5085 
5086         bfqq->wr_coeff = 1;
5087         bfqq->last_wr_start_finish = jiffies;
5088         bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
5089         bfqq->split_time = bfq_smallest_from_now();
5090 
5091         /*
5092          * To not forget the possibly high bandwidth consumed by a
5093          * process/queue in the recent past,
5094          * bfq_bfqq_softrt_next_start() returns a value at least equal
5095          * to the current value of bfqq->soft_rt_next_start (see
5096          * comments on bfq_bfqq_softrt_next_start).  Set
5097          * soft_rt_next_start to now, to mean that bfqq has consumed
5098          * no bandwidth so far.
5099          */
5100         bfqq->soft_rt_next_start = jiffies;
5101 
5102         /* first request is almost certainly seeky */
5103         bfqq->seek_history = 1;
5104 }
5105 
5106 static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
5107                                                struct bfq_group *bfqg,
5108                                                int ioprio_class, int ioprio)
5109 {
5110         switch (ioprio_class) {
5111         case IOPRIO_CLASS_RT:
5112                 return &bfqg->async_bfqq[0][ioprio];
5113         case IOPRIO_CLASS_NONE:
5114                 ioprio = IOPRIO_NORM;
5115                 /* fall through */
5116         case IOPRIO_CLASS_BE:
5117                 return &bfqg->async_bfqq[1][ioprio];
5118         case IOPRIO_CLASS_IDLE:
5119                 return &bfqg->async_idle_bfqq;
5120         default:
5121                 return NULL;
5122         }
5123 }
5124 
5125 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5126                                        struct bio *bio, bool is_sync,
5127                                        struct bfq_io_cq *bic)
5128 {
5129         const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5130         const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5131         struct bfq_queue **async_bfqq = NULL;
5132         struct bfq_queue *bfqq;
5133         struct bfq_group *bfqg;
5134 
5135         rcu_read_lock();
5136 
5137         bfqg = bfq_find_set_group(bfqd, __bio_blkcg(bio));
5138         if (!bfqg) {
5139                 bfqq = &bfqd->oom_bfqq;
5140                 goto out;
5141         }
5142 
5143         if (!is_sync) {
5144                 async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
5145                                                   ioprio);
5146                 bfqq = *async_bfqq;
5147                 if (bfqq)
5148                         goto out;
5149         }
5150 
5151         bfqq = kmem_cache_alloc_node(bfq_pool,
5152                                      GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
5153                                      bfqd->queue->node);
5154 
5155         if (bfqq) {
5156                 bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
5157                               is_sync);
5158                 bfq_init_entity(&bfqq->entity, bfqg);
5159                 bfq_log_bfqq(bfqd, bfqq, "allocated");
5160         } else {
5161                 bfqq = &bfqd->oom_bfqq;
5162                 bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
5163                 goto out;
5164         }
5165 
5166         /*
5167          * Pin the queue now that it's allocated, scheduler exit will
5168          * prune it.
5169          */
5170         if (async_bfqq) {
5171                 bfqq->ref++; /*
5172                               * Extra group reference, w.r.t. sync
5173                               * queue. This extra reference is removed
5174                               * only if bfqq->bfqg disappears, to
5175                               * guarantee that this queue is not freed
5176                               * until its group goes away.
5177                               */
5178                 bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
5179                              bfqq, bfqq->ref);
5180                 *async_bfqq = bfqq;
5181         }
5182 
5183 out:
5184         bfqq->ref++; /* get a process reference to this queue */
5185         bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref);
5186         rcu_read_unlock();
5187         return bfqq;
5188 }
5189 
5190 static void bfq_update_io_thinktime(struct bfq_data *bfqd,
5191                                     struct bfq_queue *bfqq)
5192 {
5193         struct bfq_ttime *ttime = &bfqq->ttime;
5194         u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
5195 
5196         elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
5197 
5198         ttime->ttime_samples = (7*bfqq->ttime.ttime_samples + 256) / 8;
5199         ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed,  8);
5200         ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
5201                                      ttime->ttime_samples);
5202 }
5203 
5204 static void
5205 bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5206                        struct request *rq)
5207 {
5208         bfqq->seek_history <<= 1;
5209         bfqq->seek_history |= BFQ_RQ_SEEKY(bfqd, bfqq->last_request_pos, rq);
5210 
5211         if (bfqq->wr_coeff > 1 &&
5212             bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
5213             BFQQ_TOTALLY_SEEKY(bfqq))
5214                 bfq_bfqq_end_wr(bfqq);
5215 }
5216 
5217 static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
5218                                        struct bfq_queue *bfqq,
5219                                        struct bfq_io_cq *bic)
5220 {
5221         bool has_short_ttime = true, state_changed;
5222 
5223         /*
5224          * No need to update has_short_ttime if bfqq is async or in
5225          * idle io prio class, or if bfq_slice_idle is zero, because
5226          * no device idling is performed for bfqq in this case.
5227          */
5228         if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
5229             bfqd->bfq_slice_idle == 0)
5230                 return;
5231 
5232         /* Idle window just restored, statistics are meaningless. */
5233         if (time_is_after_eq_jiffies(bfqq->split_time +
5234                                      bfqd->bfq_wr_min_idle_time))
5235                 return;
5236 
5237         /* Think time is infinite if no process is linked to
5238          * bfqq. Otherwise check average think time to
5239          * decide whether to mark as has_short_ttime
5240          */
5241         if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
5242             (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
5243              bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle))
5244                 has_short_ttime = false;
5245 
5246         state_changed = has_short_ttime != bfq_bfqq_has_short_ttime(bfqq);
5247 
5248         if (has_short_ttime)
5249                 bfq_mark_bfqq_has_short_ttime(bfqq);
5250         else
5251                 bfq_clear_bfqq_has_short_ttime(bfqq);
5252 
5253         /*
5254          * Until the base value for the total service time gets
5255          * finally computed for bfqq, the inject limit does depend on
5256          * the think-time state (short|long). In particular, the limit
5257          * is 0 or 1 if the think time is deemed, respectively, as
5258          * short or long (details in the comments in
5259          * bfq_update_inject_limit()). Accordingly, the next
5260          * instructions reset the inject limit if the think-time state
5261          * has changed and the above base value is still to be
5262          * computed.
5263          *
5264          * However, the reset is performed only if more than 100 ms
5265          * have elapsed since the last update of the inject limit, or
5266          * (inclusive) if the change is from short to long think
5267          * time. The reason for this waiting is as follows.
5268          *
5269          * bfqq may have a long think time because of a
5270          * synchronization with some other queue, i.e., because the
5271          * I/O of some other queue may need to be completed for bfqq
5272          * to receive new I/O. Details in the comments on the choice
5273          * of the queue for injection in bfq_select_queue().
5274          *
5275          * As stressed in those comments, if such a synchronization is
5276          * actually in place, then, without injection on bfqq, the
5277          * blocking I/O cannot happen to served while bfqq is in
5278          * service. As a consequence, if bfqq is granted
5279          * I/O-dispatch-plugging, then bfqq remains empty, and no I/O
5280          * is dispatched, until the idle timeout fires. This is likely
5281          * to result in lower bandwidth and higher latencies for bfqq,
5282          * and in a severe loss of total throughput.
5283          *
5284          * On the opposite end, a non-zero inject limit may allow the
5285          * I/O that blocks bfqq to be executed soon, and therefore
5286          * bfqq to receive new I/O soon.
5287          *
5288          * But, if the blocking gets actually eliminated, then the
5289          * next think-time sample for bfqq may be very low. This in
5290          * turn may cause bfqq's think time to be deemed
5291          * short. Without the 100 ms barrier, this new state change
5292          * would cause the body of the next if to be executed
5293          * immediately. But this would set to 0 the inject
5294          * limit. Without injection, the blocking I/O would cause the
5295          * think time of bfqq to become long again, and therefore the
5296          * inject limit to be raised again, and so on. The only effect
5297          * of such a steady oscillation between the two think-time
5298          * states would be to prevent effective injection on bfqq.
5299          *
5300          * In contrast, if the inject limit is not reset during such a
5301          * long time interval as 100 ms, then the number of short
5302          * think time samples can grow significantly before the reset
5303          * is performed. As a consequence, the think time state can
5304          * become stable before the reset. Therefore there will be no
5305          * state change when the 100 ms elapse, and no reset of the
5306          * inject limit. The inject limit remains steadily equal to 1
5307          * both during and after the 100 ms. So injection can be
5308          * performed at all times, and throughput gets boosted.
5309          *
5310          * An inject limit equal to 1 is however in conflict, in
5311          * general, with the fact that the think time of bfqq is
5312          * short, because injection may be likely to delay bfqq's I/O
5313          * (as explained in the comments in
5314          * bfq_update_inject_limit()). But this does not happen in
5315          * this special case, because bfqq's low think time is due to
5316          * an effective handling of a synchronization, through
5317          * injection. In this special case, bfqq's I/O does not get
5318          * delayed by injection; on the contrary, bfqq's I/O is
5319          * brought forward, because it is not blocked for
5320          * milliseconds.
5321          *
5322          * In addition, serving the blocking I/O much sooner, and much
5323          * more frequently than once per I/O-plugging timeout, makes
5324          * it much quicker to detect a waker queue (the concept of
5325          * waker queue is defined in the comments in
5326          * bfq_add_request()). This makes it possible to start sooner
5327          * to boost throughput more effectively, by injecting the I/O
5328          * of the waker queue unconditionally on every
5329          * bfq_dispatch_request().
5330          *
5331          * One last, important benefit of not resetting the inject
5332          * limit before 100 ms is that, during this time interval, the
5333          * base value for the total service time is likely to get
5334          * finally computed for bfqq, freeing the inject limit from
5335          * its relation with the think time.
5336          */
5337         if (state_changed && bfqq->last_serv_time_ns == 0 &&
5338             (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
5339                                       msecs_to_jiffies(100)) ||
5340              !has_short_ttime))
5341                 bfq_reset_inject_limit(bfqd, bfqq);
5342 }
5343 
5344 /*
5345  * Called when a new fs request (rq) is added to bfqq.  Check if there's
5346  * something we should do about it.
5347  */
5348 static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5349                             struct request *rq)
5350 {
5351         if (rq->cmd_flags & REQ_META)
5352                 bfqq->meta_pending++;
5353 
5354         bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
5355 
5356         if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
5357                 bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
5358                                  blk_rq_sectors(rq) < 32;
5359                 bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
5360 
5361                 /*
5362                  * There is just this request queued: if
5363                  * - the request is small, and
5364                  * - we are idling to boost throughput, and
5365                  * - the queue is not to be expired,
5366                  * then just exit.
5367                  *
5368                  * In this way, if the device is being idled to wait
5369                  * for a new request from the in-service queue, we
5370                  * avoid unplugging the device and committing the
5371                  * device to serve just a small request. In contrast
5372                  * we wait for the block layer to decide when to
5373                  * unplug the device: hopefully, new requests will be
5374                  * merged to this one quickly, then the device will be
5375                  * unplugged and larger requests will be dispatched.
5376                  */
5377                 if (small_req && idling_boosts_thr_without_issues(bfqd, bfqq) &&
5378                     !budget_timeout)
5379                         return;
5380 
5381                 /*
5382                  * A large enough request arrived, or idling is being
5383                  * performed to preserve service guarantees, or
5384                  * finally the queue is to be expired: in all these
5385                  * cases disk idling is to be stopped, so clear
5386                  * wait_request flag and reset timer.
5387                  */
5388                 bfq_clear_bfqq_wait_request(bfqq);
5389                 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
5390 
5391                 /*
5392                  * The queue is not empty, because a new request just
5393                  * arrived. Hence we can safely expire the queue, in
5394                  * case of budget timeout, without risking that the
5395                  * timestamps of the queue are not updated correctly.
5396                  * See [1] for more details.
5397                  */
5398                 if (budget_timeout)
5399                         bfq_bfqq_expire(bfqd, bfqq, false,
5400                                         BFQQE_BUDGET_TIMEOUT);
5401         }
5402 }
5403 
5404 /* returns true if it causes the idle timer to be disabled */
5405 static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
5406 {
5407         struct bfq_queue *bfqq = RQ_BFQQ(rq),
5408                 *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true);
5409         bool waiting, idle_timer_disabled = false;
5410 
5411         if (new_bfqq) {
5412                 /*
5413                  * Release the request's reference to the old bfqq
5414                  * and make sure one is taken to the shared queue.
5415                  */
5416                 new_bfqq->allocated++;
5417                 bfqq->allocated--;
5418                 new_bfqq->ref++;
5419                 /*
5420                  * If the bic associated with the process
5421                  * issuing this request still points to bfqq
5422                  * (and thus has not been already redirected
5423                  * to new_bfqq or even some other bfq_queue),
5424                  * then complete the merge and redirect it to
5425                  * new_bfqq.
5426                  */
5427                 if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
5428                         bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
5429                                         bfqq, new_bfqq);
5430 
5431                 bfq_clear_bfqq_just_created(bfqq);
5432                 /*
5433                  * rq is about to be enqueued into new_bfqq,
5434                  * release rq reference on bfqq
5435                  */
5436                 bfq_put_queue(bfqq);
5437                 rq->elv.priv[1] = new_bfqq;
5438                 bfqq = new_bfqq;
5439         }
5440 
5441         bfq_update_io_thinktime(bfqd, bfqq);
5442         bfq_update_has_short_ttime(bfqd, bfqq, RQ_BIC(rq));
5443         bfq_update_io_seektime(bfqd, bfqq, rq);
5444 
5445         waiting = bfqq && bfq_bfqq_wait_request(bfqq);
5446         bfq_add_request(rq);
5447         idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq);
5448 
5449         rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
5450         list_add_tail(&rq->queuelist, &bfqq->fifo);
5451 
5452         bfq_rq_enqueued(bfqd, bfqq, rq);
5453 
5454         return idle_timer_disabled;
5455 }
5456 
5457 #ifdef CONFIG_BFQ_CGROUP_DEBUG
5458 static void bfq_update_insert_stats(struct request_queue *q,
5459                                     struct bfq_queue *bfqq,
5460                                     bool idle_timer_disabled,
5461                                     unsigned int cmd_flags)
5462 {
5463         if (!bfqq)
5464                 return;
5465 
5466         /*
5467          * bfqq still exists, because it can disappear only after
5468          * either it is merged with another queue, or the process it
5469          * is associated with exits. But both actions must be taken by
5470          * the same process currently executing this flow of
5471          * instructions.
5472          *
5473          * In addition, the following queue lock guarantees that
5474          * bfqq_group(bfqq) exists as well.
5475          */
5476         spin_lock_irq(&q->queue_lock);
5477         bfqg_stats_update_io_add(bfqq_group(bfqq), bfqq, cmd_flags);
5478         if (idle_timer_disabled)
5479                 bfqg_stats_update_idle_time(bfqq_group(bfqq));
5480         spin_unlock_irq(&q->queue_lock);
5481 }
5482 #else
5483 static inline void bfq_update_insert_stats(struct request_queue *q,
5484                                            struct bfq_queue *bfqq,
5485                                            bool idle_timer_disabled,
5486                                            unsigned int cmd_flags) {}
5487 #endif /* CONFIG_BFQ_CGROUP_DEBUG */
5488 
5489 static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
5490                                bool at_head)
5491 {
5492         struct request_queue *q = hctx->queue;
5493         struct bfq_data *bfqd = q->elevator->elevator_data;
5494         struct bfq_queue *bfqq;
5495         bool idle_timer_disabled = false;
5496         unsigned int cmd_flags;
5497 
5498 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5499         if (!cgroup_subsys_on_dfl(io_cgrp_subsys) && rq->bio)
5500                 bfqg_stats_update_legacy_io(q, rq);
5501 #endif
5502         spin_lock_irq(&bfqd->lock);
5503         if (blk_mq_sched_try_insert_merge(q, rq)) {
5504                 spin_unlock_irq(&bfqd->lock);
5505                 return;
5506         }
5507 
5508         spin_unlock_irq(&bfqd->lock);
5509 
5510         blk_mq_sched_request_inserted(rq);
5511 
5512         spin_lock_irq(&bfqd->lock);
5513         bfqq = bfq_init_rq(rq);
5514         if (!bfqq || at_head || blk_rq_is_passthrough(rq)) {
5515                 if (at_head)
5516                         list_add(&rq->queuelist, &bfqd->dispatch);
5517                 else
5518                         list_add_tail(&rq->queuelist, &bfqd->dispatch);
5519         } else {
5520                 idle_timer_disabled = __bfq_insert_request(bfqd, rq);
5521                 /*
5522                  * Update bfqq, because, if a queue merge has occurred
5523                  * in __bfq_insert_request, then rq has been
5524                  * redirected into a new queue.
5525                  */
5526                 bfqq = RQ_BFQQ(rq);
5527 
5528                 if (rq_mergeable(rq)) {
5529                         elv_rqhash_add(q, rq);
5530                         if (!q->last_merge)
5531                                 q->last_merge = rq;
5532                 }
5533         }
5534 
5535         /*
5536          * Cache cmd_flags before releasing scheduler lock, because rq
5537          * may disappear afterwards (for example, because of a request
5538          * merge).
5539          */
5540         cmd_flags = rq->cmd_flags;
5541 
5542         spin_unlock_irq(&bfqd->lock);
5543 
5544         bfq_update_insert_stats(q, bfqq, idle_timer_disabled,
5545                                 cmd_flags);
5546 }
5547 
5548 static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
5549                                 struct list_head *list, bool at_head)
5550 {
5551         while (!list_empty(list)) {
5552                 struct request *rq;
5553 
5554                 rq = list_first_entry(list, struct request, queuelist);
5555                 list_del_init(&rq->queuelist);
5556                 bfq_insert_request(hctx, rq, at_head);
5557         }
5558 }
5559 
5560 static void bfq_update_hw_tag(struct bfq_data *bfqd)
5561 {
5562         struct bfq_queue *bfqq = bfqd->in_service_queue;
5563 
5564         bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
5565                                        bfqd->rq_in_driver);
5566 
5567         if (bfqd->hw_tag == 1)
5568                 return;
5569 
5570         /*
5571          * This sample is valid if the number of outstanding requests
5572          * is large enough to allow a queueing behavior.  Note that the
5573          * sum is not exact, as it's not taking into account deactivated
5574          * requests.
5575          */
5576         if (bfqd->rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD)
5577                 return;
5578 
5579         /*
5580          * If active queue hasn't enough requests and can idle, bfq might not
5581          * dispatch sufficient requests to hardware. Don't zero hw_tag in this
5582          * case
5583          */
5584         if (bfqq && bfq_bfqq_has_short_ttime(bfqq) &&
5585             bfqq->dispatched + bfqq->queued[0] + bfqq->queued[1] <
5586             BFQ_HW_QUEUE_THRESHOLD &&
5587             bfqd->rq_in_driver < BFQ_HW_QUEUE_THRESHOLD)
5588                 return;
5589 
5590         if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
5591                 return;
5592 
5593         bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
5594         bfqd->max_rq_in_driver = 0;
5595         bfqd->hw_tag_samples = 0;
5596 
5597         bfqd->nonrot_with_queueing =
5598                 blk_queue_nonrot(bfqd->queue) && bfqd->hw_tag;
5599 }
5600 
5601 static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
5602 {
5603         u64 now_ns;
5604         u32 delta_us;
5605 
5606         bfq_update_hw_tag(bfqd);
5607 
5608         bfqd->rq_in_driver--;
5609         bfqq->dispatched--;
5610 
5611         if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
5612                 /*
5613                  * Set budget_timeout (which we overload to store the
5614                  * time at which the queue remains with no backlog and
5615                  * no outstanding request; used by the weight-raising
5616                  * mechanism).
5617                  */
5618                 bfqq->budget_timeout = jiffies;
5619 
5620                 bfq_weights_tree_remove(bfqd, bfqq);
5621         }
5622 
5623         now_ns = ktime_get_ns();
5624 
5625         bfqq->ttime.last_end_request = now_ns;
5626 
5627         /*
5628          * Using us instead of ns, to get a reasonable precision in
5629          * computing rate in next check.
5630          */
5631         delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);
5632 
5633         /*
5634          * If the request took rather long to complete, and, according
5635          * to the maximum request size recorded, this completion latency
5636          * implies that the request was certainly served at a very low
5637          * rate (less than 1M sectors/sec), then the whole observation
5638          * interval that lasts up to this time instant cannot be a
5639          * valid time interval for computing a new peak rate.  Invoke
5640          * bfq_update_rate_reset to have the following three steps
5641          * taken:
5642          * - close the observation interval at the last (previous)
5643          *   request dispatch or completion
5644          * - compute rate, if possible, for that observation interval
5645          * - reset to zero samples, which will trigger a proper
5646          *   re-initialization of the observation interval on next
5647          *   dispatch
5648          */
5649         if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
5650            (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
5651                         1UL<<(BFQ_RATE_SHIFT - 10))
5652                 bfq_update_rate_reset(bfqd, NULL);
5653         bfqd->last_completion = now_ns;
5654         bfqd->last_completed_rq_bfqq = bfqq;
5655 
5656         /*
5657          * If we are waiting to discover whether the request pattern
5658          * of the task associated with the queue is actually
5659          * isochronous, and both requisites for this condition to hold
5660          * are now satisfied, then compute soft_rt_next_start (see the
5661          * comments on the function bfq_bfqq_softrt_next_start()). We
5662          * do not compute soft_rt_next_start if bfqq is in interactive
5663          * weight raising (see the comments in bfq_bfqq_expire() for
5664          * an explanation). We schedule this delayed update when bfqq
5665          * expires, if it still has in-flight requests.
5666          */
5667         if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
5668             RB_EMPTY_ROOT(&bfqq->sort_list) &&
5669             bfqq->wr_coeff != bfqd->bfq_wr_coeff)
5670                 bfqq->soft_rt_next_start =
5671                         bfq_bfqq_softrt_next_start(bfqd, bfqq);
5672 
5673         /*
5674          * If this is the in-service queue, check if it needs to be expired,
5675          * or if we want to idle in case it has no pending requests.
5676          */
5677         if (bfqd->in_service_queue == bfqq) {
5678                 if (bfq_bfqq_must_idle(bfqq)) {
5679                         if (bfqq->dispatched == 0)
5680                                 bfq_arm_slice_timer(bfqd);
5681                         /*
5682                          * If we get here, we do not expire bfqq, even
5683                          * if bfqq was in budget timeout or had no
5684                          * more requests (as controlled in the next
5685                          * conditional instructions). The reason for
5686                          * not expiring bfqq is as follows.
5687                          *
5688                          * Here bfqq->dispatched > 0 holds, but
5689                          * bfq_bfqq_must_idle() returned true. This
5690                          * implies that, even if no request arrives
5691                          * for bfqq before bfqq->dispatched reaches 0,
5692                          * bfqq will, however, not be expired on the
5693                          * completion event that causes bfqq->dispatch
5694                          * to reach zero. In contrast, on this event,
5695                          * bfqq will start enjoying device idling
5696                          * (I/O-dispatch plugging).
5697                          *
5698                          * But, if we expired bfqq here, bfqq would
5699                          * not have the chance to enjoy device idling
5700                          * when bfqq->dispatched finally reaches
5701                          * zero. This would expose bfqq to violation
5702                          * of its reserved service guarantees.
5703                          */
5704                         return;
5705                 } else if (bfq_may_expire_for_budg_timeout(bfqq))
5706                         bfq_bfqq_expire(bfqd, bfqq, false,
5707                                         BFQQE_BUDGET_TIMEOUT);
5708                 else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
5709                          (bfqq->dispatched == 0 ||
5710                           !bfq_better_to_idle(bfqq)))
5711                         bfq_bfqq_expire(bfqd, bfqq, false,
5712                                         BFQQE_NO_MORE_REQUESTS);
5713         }
5714 
5715         if (!bfqd->rq_in_driver)
5716                 bfq_schedule_dispatch(bfqd);
5717 }
5718 
5719 static void bfq_finish_requeue_request_body(struct bfq_queue *bfqq)
5720 {
5721         bfqq->allocated--;
5722 
5723         bfq_put_queue(bfqq);
5724 }
5725 
5726 /*
5727  * The processes associated with bfqq may happen to generate their
5728  * cumulative I/O at a lower rate than the rate at which the device
5729  * could serve the same I/O. This is rather probable, e.g., if only
5730  * one process is associated with bfqq and the device is an SSD. It
5731  * results in bfqq becoming often empty while in service. In this
5732  * respect, if BFQ is allowed to switch to another queue when bfqq
5733  * remains empty, then the device goes on being fed with I/O requests,
5734  * and the throughput is not affected. In contrast, if BFQ is not
5735  * allowed to switch to another queue---because bfqq is sync and
5736  * I/O-dispatch needs to be plugged while bfqq is temporarily
5737  * empty---then, during the service of bfqq, there will be frequent
5738  * "service holes", i.e., time intervals during which bfqq gets empty
5739  * and the device can only consume the I/O already queued in its
5740  * hardware queues. During service holes, the device may even get to
5741  * remaining idle. In the end, during the service of bfqq, the device
5742  * is driven at a lower speed than the one it can reach with the kind
5743  * of I/O flowing through bfqq.
5744  *
5745  * To counter this loss of throughput, BFQ implements a "request
5746  * injection mechanism", which tries to fill the above service holes
5747  * with I/O requests taken from other queues. The hard part in this
5748  * mechanism is finding the right amount of I/O to inject, so as to
5749  * both boost throughput and not break bfqq's bandwidth and latency
5750  * guarantees. In this respect, the mechanism maintains a per-queue
5751  * inject limit, computed as below. While bfqq is empty, the injection
5752  * mechanism dispatches extra I/O requests only until the total number
5753  * of I/O requests in flight---i.e., already dispatched but not yet
5754  * completed---remains lower than this limit.
5755  *
5756  * A first definition comes in handy to introduce the algorithm by
5757  * which the inject limit is computed.  We define as first request for
5758  * bfqq, an I/O request for bfqq that arrives while bfqq is in
5759  * service, and causes bfqq to switch from empty to non-empty. The
5760  * algorithm updates the limit as a function of the effect of
5761  * injection on the service times of only the first requests of
5762  * bfqq. The reason for this restriction is that these are the
5763  * requests whose service time is affected most, because they are the
5764  * first to arrive after injection possibly occurred.
5765  *
5766  * To evaluate the effect of injection, the algorithm measures the
5767  * "total service time" of first requests. We define as total service
5768  * time of an I/O request, the time that elapses since when the
5769  * request is enqueued into bfqq, to when it is completed. This
5770  * quantity allows the whole effect of injection to be measured. It is
5771  * easy to see why. Suppose that some requests of other queues are
5772  * actually injected while bfqq is empty, and that a new request R
5773  * then arrives for bfqq. If the device does start to serve all or
5774  * part of the injected requests during the service hole, then,
5775  * because of this extra service, it may delay the next invocation of
5776  * the dispatch hook of BFQ. Then, even after R gets eventually
5777  * dispatched, the device may delay the actual service of R if it is
5778  * still busy serving the extra requests, or if it decides to serve,
5779  * before R, some extra request still present in its queues. As a
5780  * conclusion, the cumulative extra delay caused by injection can be
5781  * easily evaluated by just comparing the total service time of first
5782  * requests with and without injection.
5783  *
5784  * The limit-update algorithm works as follows. On the arrival of a
5785  * first request of bfqq, the algorithm measures the total time of the
5786  * request only if one of the three cases below holds, and, for each
5787  * case, it updates the limit as described below:
5788  *
5789  * (1) If there is no in-flight request. This gives a baseline for the
5790  *     total service time of the requests of bfqq. If the baseline has
5791  *     not been computed yet, then, after computing it, the limit is
5792  *     set to 1, to start boosting throughput, and to prepare the
5793  *     ground for the next case. If the baseline has already been
5794  *     computed, then it is updated, in case it results to be lower
5795  *     than the previous value.
5796  *
5797  * (2) If the limit is higher than 0 and there are in-flight
5798  *     requests. By comparing the total service time in this case with
5799  *     the above baseline, it is possible to know at which extent the
5800  *     current value of the limit is inflating the total service
5801  *     time. If the inflation is below a certain threshold, then bfqq
5802  *     is assumed to be suffering from no perceivable loss of its
5803  *     service guarantees, and the limit is even tentatively
5804  *     increased. If the inflation is above the threshold, then the
5805  *     limit is decreased. Due to the lack of any hysteresis, this
5806  *     logic makes the limit oscillate even in steady workload
5807  *     conditions. Yet we opted for it, because it is fast in reaching
5808  *     the best value for the limit, as a function of the current I/O
5809  *     workload. To reduce oscillations, this step is disabled for a
5810  *     short time interval after the limit happens to be decreased.
5811  *
5812  * (3) Periodically, after resetting the limit, to make sure that the
5813  *     limit eventually drops in case the workload changes. This is
5814  *     needed because, after the limit has gone safely up for a
5815  *     certain workload, it is impossible to guess whether the
5816  *     baseline total service time may have changed, without measuring
5817  *     it again without injection. A more effective version of this
5818  *     step might be to just sample the baseline, by interrupting
5819  *     injection only once, and then to reset/lower the limit only if
5820  *     the total service time with the current limit does happen to be
5821  *     too large.
5822  *
5823  * More details on each step are provided in the comments on the
5824  * pieces of code that implement these steps: the branch handling the
5825  * transition from empty to non empty in bfq_add_request(), the branch
5826  * handling injection in bfq_select_queue(), and the function
5827  * bfq_choose_bfqq_for_injection(). These comments also explain some
5828  * exceptions, made by the injection mechanism in some special cases.
5829  */
5830 static void bfq_update_inject_limit(struct bfq_data *bfqd,
5831                                     struct bfq_queue *bfqq)
5832 {
5833         u64 tot_time_ns = ktime_get_ns() - bfqd->last_empty_occupied_ns;
5834         unsigned int old_limit = bfqq->inject_limit;
5835 
5836         if (bfqq->last_serv_time_ns > 0 && bfqd->rqs_injected) {
5837                 u64 threshold = (bfqq->last_serv_time_ns * 3)>>1;
5838 
5839                 if (tot_time_ns >= threshold && old_limit > 0) {
5840                         bfqq->inject_limit--;
5841                         bfqq->decrease_time_jif = jiffies;
5842                 } else if (tot_time_ns < threshold &&
5843                            old_limit <= bfqd->max_rq_in_driver)
5844                         bfqq->inject_limit++;
5845         }
5846 
5847         /*
5848          * Either we still have to compute the base value for the
5849          * total service time, and there seem to be the right
5850          * conditions to do it, or we can lower the last base value
5851          * computed.
5852          *
5853          * NOTE: (bfqd->rq_in_driver == 1) means that there is no I/O
5854          * request in flight, because this function is in the code
5855          * path that handles the completion of a request of bfqq, and,
5856          * in particular, this function is executed before
5857          * bfqd->rq_in_driver is decremented in such a code path.
5858          */
5859         if ((bfqq->last_serv_time_ns == 0 && bfqd->rq_in_driver == 1) ||
5860             tot_time_ns < bfqq->last_serv_time_ns) {
5861                 if (bfqq->last_serv_time_ns == 0) {
5862                         /*
5863                          * Now we certainly have a base value: make sure we
5864                          * start trying injection.
5865                          */
5866                         bfqq->inject_limit = max_t(unsigned int, 1, old_limit);
5867                 }
5868                 bfqq->last_serv_time_ns = tot_time_ns;
5869         } else if (!bfqd->rqs_injected && bfqd->rq_in_driver == 1)
5870                 /*
5871                  * No I/O injected and no request still in service in
5872                  * the drive: these are the exact conditions for
5873                  * computing the base value of the total service time
5874                  * for bfqq. So let's update this value, because it is
5875                  * rather variable. For example, it varies if the size
5876                  * or the spatial locality of the I/O requests in bfqq
5877                  * change.
5878                  */
5879                 bfqq->last_serv_time_ns = tot_time_ns;
5880 
5881 
5882         /* update complete, not waiting for any request completion any longer */
5883         bfqd->waited_rq = NULL;
5884         bfqd->rqs_injected = false;
5885 }
5886 
5887 /*
5888  * Handle either a requeue or a finish for rq. The things to do are
5889  * the same in both cases: all references to rq are to be dropped. In
5890  * particular, rq is considered completed from the point of view of
5891  * the scheduler.
5892  */
5893 static void bfq_finish_requeue_request(struct request *rq)
5894 {
5895         struct bfq_queue *bfqq = RQ_BFQQ(rq);
5896         struct bfq_data *bfqd;
5897 
5898         /*
5899          * Requeue and finish hooks are invoked in blk-mq without
5900          * checking whether the involved request is actually still
5901          * referenced in the scheduler. To handle this fact, the
5902          * following two checks make this function exit in case of
5903          * spurious invocations, for which there is nothing to do.
5904          *
5905          * First, check whether rq has nothing to do with an elevator.
5906          */
5907         if (unlikely(!(rq->rq_flags & RQF_ELVPRIV)))
5908                 return;
5909 
5910         /*
5911          * rq either is not associated with any icq, or is an already
5912          * requeued request that has not (yet) been re-inserted into
5913          * a bfq_queue.
5914          */
5915         if (!rq->elv.icq || !bfqq)
5916                 return;
5917 
5918         bfqd = bfqq->bfqd;
5919 
5920         if (rq->rq_flags & RQF_STARTED)
5921                 bfqg_stats_update_completion(bfqq_group(bfqq),
5922                                              rq->start_time_ns,
5923                                              rq->io_start_time_ns,
5924                                              rq->cmd_flags);
5925 
5926         if (likely(rq->rq_flags & RQF_STARTED)) {
5927                 unsigned long flags;
5928 
5929                 spin_lock_irqsave(&bfqd->lock, flags);
5930 
5931                 if (rq == bfqd->waited_rq)
5932                         bfq_update_inject_limit(bfqd, bfqq);
5933 
5934                 bfq_completed_request(bfqq, bfqd);
5935                 bfq_finish_requeue_request_body(bfqq);
5936 
5937                 spin_unlock_irqrestore(&bfqd->lock, flags);
5938         } else {
5939                 /*
5940                  * Request rq may be still/already in the scheduler,
5941                  * in which case we need to remove it (this should
5942                  * never happen in case of requeue). And we cannot
5943                  * defer such a check and removal, to avoid
5944                  * inconsistencies in the time interval from the end
5945                  * of this function to the start of the deferred work.
5946                  * This situation seems to occur only in process
5947                  * context, as a consequence of a merge. In the
5948                  * current version of the code, this implies that the
5949                  * lock is held.
5950                  */
5951 
5952                 if (!RB_EMPTY_NODE(&rq->rb_node)) {
5953                         bfq_remove_request(rq->q, rq);
5954                         bfqg_stats_update_io_remove(bfqq_group(bfqq),
5955                                                     rq->cmd_flags);
5956                 }
5957                 bfq_finish_requeue_request_body(bfqq);
5958         }
5959 
5960         /*
5961          * Reset private fields. In case of a requeue, this allows
5962          * this function to correctly do nothing if it is spuriously
5963          * invoked again on this same request (see the check at the
5964          * beginning of the function). Probably, a better general
5965          * design would be to prevent blk-mq from invoking the requeue
5966          * or finish hooks of an elevator, for a request that is not
5967          * referred by that elevator.
5968          *
5969          * Resetting the following fields would break the
5970          * request-insertion logic if rq is re-inserted into a bfq
5971          * internal queue, without a re-preparation. Here we assume
5972          * that re-insertions of requeued requests, without
5973          * re-preparation, can happen only for pass_through or at_head
5974          * requests (which are not re-inserted into bfq internal
5975          * queues).
5976          */
5977         rq->elv.priv[0] = NULL;
5978         rq->elv.priv[1] = NULL;
5979 }
5980 
5981 /*
5982  * Removes the association between the current task and bfqq, assuming
5983  * that bic points to the bfq iocontext of the task.
5984  * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
5985  * was the last process referring to that bfqq.
5986  */
5987 static struct bfq_queue *
5988 bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
5989 {
5990         bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
5991 
5992         if (bfqq_process_refs(bfqq) == 1) {
5993                 bfqq->pid = current->pid;
5994                 bfq_clear_bfqq_coop(bfqq);
5995                 bfq_clear_bfqq_split_coop(bfqq);
5996                 return bfqq;
5997         }
5998 
5999         bic_set_bfqq(bic, NULL, 1);
6000 
6001         bfq_put_cooperator(bfqq);
6002 
6003         bfq_release_process_ref(bfqq->bfqd, bfqq);
6004         return NULL;
6005 }
6006 
6007 static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
6008                                                    struct bfq_io_cq *bic,
6009                                                    struct bio *bio,
6010                                                    bool split, bool is_sync,
6011                                                    bool *new_queue)
6012 {
6013         struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
6014 
6015         if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
6016                 return bfqq;
6017 
6018         if (new_queue)
6019                 *new_queue = true;
6020 
6021         if (bfqq)
6022                 bfq_put_queue(bfqq);
6023         bfqq = bfq_get_queue(bfqd, bio, is_sync, bic);
6024 
6025         bic_set_bfqq(bic, bfqq, is_sync);
6026         if (split && is_sync) {
6027                 if ((bic->was_in_burst_list && bfqd->large_burst) ||
6028                     bic->saved_in_large_burst)
6029                         bfq_mark_bfqq_in_large_burst(bfqq);
6030                 else {
6031                         bfq_clear_bfqq_in_large_burst(bfqq);
6032                         if (bic->was_in_burst_list)
6033                                 /*
6034                                  * If bfqq was in the current
6035                                  * burst list before being
6036                                  * merged, then we have to add
6037                                  * it back. And we do not need
6038                                  * to increase burst_size, as
6039                                  * we did not decrement
6040                                  * burst_size when we removed
6041                                  * bfqq from the burst list as
6042                                  * a consequence of a merge
6043                                  * (see comments in
6044                                  * bfq_put_queue). In this
6045                                  * respect, it would be rather
6046                                  * costly to know whether the
6047                                  * current burst list is still
6048                                  * the same burst list from
6049                                  * which bfqq was removed on
6050                                  * the merge. To avoid this
6051                                  * cost, if bfqq was in a
6052                                  * burst list, then we add
6053                                  * bfqq to the current burst
6054                                  * list without any further
6055                                  * check. This can cause
6056                                  * inappropriate insertions,
6057                                  * but rarely enough to not
6058                                  * harm the detection of large
6059                                  * bursts significantly.
6060                                  */
6061                                 hlist_add_head(&bfqq->burst_list_node,
6062                                                &bfqd->burst_list);
6063                 }
6064                 bfqq->split_time = jiffies;
6065         }
6066 
6067         return bfqq;
6068 }
6069 
6070 /*
6071  * Only reset private fields. The actual request preparation will be
6072  * performed by bfq_init_rq, when rq is either inserted or merged. See
6073  * comments on bfq_init_rq for the reason behind this delayed
6074  * preparation.
6075  */
6076 static void bfq_prepare_request(struct request *rq)
6077 {
6078         /*
6079          * Regardless of whether we have an icq attached, we have to
6080          * clear the scheduler pointers, as they might point to
6081          * previously allocated bic/bfqq structs.
6082          */
6083         rq->elv.priv[0] = rq->elv.priv[1] = NULL;
6084 }
6085 
6086 /*
6087  * If needed, init rq, allocate bfq data structures associated with
6088  * rq, and increment reference counters in the destination bfq_queue
6089  * for rq. Return the destination bfq_queue for rq, or NULL is rq is
6090  * not associated with any bfq_queue.
6091  *
6092  * This function is invoked by the functions that perform rq insertion
6093  * or merging. One may have expected the above preparation operations
6094  * to be performed in bfq_prepare_request, and not delayed to when rq
6095  * is inserted or merged. The rationale behind this delayed
6096  * preparation is that, after the prepare_request hook is invoked for
6097  * rq, rq may still be transformed into a request with no icq, i.e., a
6098  * request not associated with any queue. No bfq hook is invoked to
6099  * signal this transformation. As a consequence, should these
6100  * preparation operations be performed when the prepare_request hook
6101  * is invoked, and should rq be transformed one moment later, bfq
6102  * would end up in an inconsistent state, because it would have
6103  * incremented some queue counters for an rq destined to
6104  * transformation, without any chance to correctly lower these
6105  * counters back. In contrast, no transformation can still happen for
6106  * rq after rq has been inserted or merged. So, it is safe to execute
6107  * these preparation operations when rq is finally inserted or merged.
6108  */
6109 static struct bfq_queue *bfq_init_rq(struct request *rq)
6110 {
6111         struct request_queue *q = rq->q;
6112         struct bio *bio = rq->bio;
6113         struct bfq_data *bfqd = q->elevator->elevator_data;
6114         struct bfq_io_cq *bic;
6115         const int is_sync = rq_is_sync(rq);
6116         struct bfq_queue *bfqq;
6117         bool new_queue = false;
6118         bool bfqq_already_existing = false, split = false;
6119 
6120         if (unlikely(!rq->elv.icq))
6121                 return NULL;
6122 
6123         /*
6124          * Assuming that elv.priv[1] is set only if everything is set
6125          * for this rq. This holds true, because this function is
6126          * invoked only for insertion or merging, and, after such
6127          * events, a request cannot be manipulated any longer before
6128          * being removed from bfq.
6129          */
6130         if (rq->elv.priv[1])
6131                 return rq->elv.priv[1];
6132 
6133         bic = icq_to_bic(rq->elv.icq);
6134 
6135         bfq_check_ioprio_change(bic, bio);
6136 
6137         bfq_bic_update_cgroup(bic, bio);
6138 
6139         bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
6140                                          &new_queue);
6141 
6142         if (likely(!new_queue)) {
6143                 /* If the queue was seeky for too long, break it apart. */
6144                 if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) {
6145                         bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq");
6146 
6147                         /* Update bic before losing reference to bfqq */
6148                         if (bfq_bfqq_in_large_burst(bfqq))
6149                                 bic->saved_in_large_burst = true;
6150 
6151                         bfqq = bfq_split_bfqq(bic, bfqq);
6152                         split = true;
6153 
6154                         if (!bfqq)
6155                                 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
6156                                                                  true, is_sync,
6157                                                                  NULL);
6158                         else
6159                                 bfqq_already_existing = true;
6160                 }
6161         }
6162 
6163         bfqq->allocated++;
6164         bfqq->ref++;
6165         bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
6166                      rq, bfqq, bfqq->ref);
6167 
6168         rq->elv.priv[0] = bic;
6169         rq->elv.priv[1] = bfqq;
6170 
6171         /*
6172          * If a bfq_queue has only one process reference, it is owned
6173          * by only this bic: we can then set bfqq->bic = bic. in
6174          * addition, if the queue has also just been split, we have to
6175          * resume its state.
6176          */
6177         if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
6178                 bfqq->bic = bic;
6179                 if (split) {
6180                         /*
6181                          * The queue has just been split from a shared
6182                          * queue: restore the idle window and the
6183                          * possible weight raising period.
6184                          */
6185                         bfq_bfqq_resume_state(bfqq, bfqd, bic,
6186                                               bfqq_already_existing);
6187                 }
6188         }
6189 
6190         /*
6191          * Consider bfqq as possibly belonging to a burst of newly
6192          * created queues only if:
6193          * 1) A burst is actually happening (bfqd->burst_size > 0)
6194          * or
6195          * 2) There is no other active queue. In fact, if, in
6196          *    contrast, there are active queues not belonging to the
6197          *    possible burst bfqq may belong to, then there is no gain
6198          *    in considering bfqq as belonging to a burst, and
6199          *    therefore in not weight-raising bfqq. See comments on
6200          *    bfq_handle_burst().
6201          *
6202          * This filtering also helps eliminating false positives,
6203          * occurring when bfqq does not belong to an actual large
6204          * burst, but some background task (e.g., a service) happens
6205          * to trigger the creation of new queues very close to when
6206          * bfqq and its possible companion queues are created. See
6207          * comments on bfq_handle_burst() for further details also on
6208          * this issue.
6209          */
6210         if (unlikely(bfq_bfqq_just_created(bfqq) &&
6211                      (bfqd->burst_size > 0 ||
6212                       bfq_tot_busy_queues(bfqd) == 0)))
6213                 bfq_handle_burst(bfqd, bfqq);
6214 
6215         return bfqq;
6216 }
6217 
6218 static void
6219 bfq_idle_slice_timer_body(struct bfq_data *bfqd, struct bfq_queue *bfqq)
6220 {
6221         enum bfqq_expiration reason;
6222         unsigned long flags;
6223 
6224         spin_lock_irqsave(&bfqd->lock, flags);
6225 
6226         /*
6227          * Considering that bfqq may be in race, we should firstly check
6228          * whether bfqq is in service before doing something on it. If
6229          * the bfqq in race is not in service, it has already been expired
6230          * through __bfq_bfqq_expire func and its wait_request flags has
6231          * been cleared in __bfq_bfqd_reset_in_service func.
6232          */
6233         if (bfqq != bfqd->in_service_queue) {
6234                 spin_unlock_irqrestore(&bfqd->lock, flags);
6235                 return;
6236         }
6237 
6238         bfq_clear_bfqq_wait_request(bfqq);
6239 
6240         if (bfq_bfqq_budget_timeout(bfqq))
6241                 /*
6242                  * Also here the queue can be safely expired
6243                  * for budget timeout without wasting
6244                  * guarantees
6245                  */
6246                 reason = BFQQE_BUDGET_TIMEOUT;
6247         else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
6248                 /*
6249                  * The queue may not be empty upon timer expiration,
6250                  * because we may not disable the timer when the
6251                  * first request of the in-service queue arrives
6252                  * during disk idling.
6253                  */
6254                 reason = BFQQE_TOO_IDLE;
6255         else
6256                 goto schedule_dispatch;
6257 
6258         bfq_bfqq_expire(bfqd, bfqq, true, reason);
6259 
6260 schedule_dispatch:
6261         spin_unlock_irqrestore(&bfqd->lock, flags);
6262         bfq_schedule_dispatch(bfqd);
6263 }
6264 
6265 /*
6266  * Handler of the expiration of the timer running if the in-service queue
6267  * is idling inside its time slice.
6268  */
6269 static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
6270 {
6271         struct bfq_data *bfqd = container_of(timer, struct bfq_data,
6272                                              idle_slice_timer);
6273         struct bfq_queue *bfqq = bfqd->in_service_queue;
6274 
6275         /*
6276          * Theoretical race here: the in-service queue can be NULL or
6277          * different from the queue that was idling if a new request
6278          * arrives for the current queue and there is a full dispatch
6279          * cycle that changes the in-service queue.  This can hardly
6280          * happen, but in the worst case we just expire a queue too
6281          * early.
6282          */
6283         if (bfqq)
6284                 bfq_idle_slice_timer_body(bfqd, bfqq);
6285 
6286         return HRTIMER_NORESTART;
6287 }
6288 
6289 static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
6290                                  struct bfq_queue **bfqq_ptr)
6291 {
6292         struct bfq_queue *bfqq = *bfqq_ptr;
6293 
6294         bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
6295         if (bfqq) {
6296                 bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
6297 
6298                 bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
6299                              bfqq, bfqq->ref);
6300                 bfq_put_queue(bfqq);
6301                 *bfqq_ptr = NULL;
6302         }
6303 }
6304 
6305 /*
6306  * Release all the bfqg references to its async queues.  If we are
6307  * deallocating the group these queues may still contain requests, so
6308  * we reparent them to the root cgroup (i.e., the only one that will
6309  * exist for sure until all the requests on a device are gone).
6310  */
6311 void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
6312 {
6313         int i, j;
6314 
6315         for (i = 0; i < 2; i++)
6316                 for (j = 0; j < IOPRIO_BE_NR; j++)
6317                         __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);
6318 
6319         __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
6320 }
6321 
6322 /*
6323  * See the comments on bfq_limit_depth for the purpose of
6324  * the depths set in the function. Return minimum shallow depth we'll use.
6325  */
6326 static unsigned int bfq_update_depths(struct bfq_data *bfqd,
6327                                       struct sbitmap_queue *bt)
6328 {
6329         unsigned int i, j, min_shallow = UINT_MAX;
6330 
6331         /*
6332          * In-word depths if no bfq_queue is being weight-raised:
6333          * leaving 25% of tags only for sync reads.
6334          *
6335          * In next formulas, right-shift the value
6336          * (1U<<bt->sb.shift), instead of computing directly
6337          * (1U<<(bt->sb.shift - something)), to be robust against
6338          * any possible value of bt->sb.shift, without having to
6339          * limit 'something'.
6340          */
6341         /* no more than 50% of tags for async I/O */
6342         bfqd->word_depths[0][0] = max((1U << bt->sb.shift) >> 1, 1U);
6343         /*
6344          * no more than 75% of tags for sync writes (25% extra tags
6345          * w.r.t. async I/O, to prevent async I/O from starving sync
6346          * writes)
6347          */
6348         bfqd->word_depths[0][1] = max(((1U << bt->sb.shift) * 3) >> 2, 1U);
6349 
6350         /*
6351          * In-word depths in case some bfq_queue is being weight-
6352          * raised: leaving ~63% of tags for sync reads. This is the
6353          * highest percentage for which, in our tests, application
6354          * start-up times didn't suffer from any regression due to tag
6355          * shortage.
6356          */
6357         /* no more than ~18% of tags for async I/O */
6358         bfqd->word_depths[1][0] = max(((1U << bt->sb.shift) * 3) >> 4, 1U);
6359         /* no more than ~37% of tags for sync writes (~20% extra tags) */
6360         bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U);
6361 
6362         for (i = 0; i < 2; i++)
6363                 for (j = 0; j < 2; j++)
6364                         min_shallow = min(min_shallow, bfqd->word_depths[i][j]);
6365 
6366         return min_shallow;
6367 }
6368 
6369 static void bfq_depth_updated(struct blk_mq_hw_ctx *hctx)
6370 {
6371         struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
6372         struct blk_mq_tags *tags = hctx->sched_tags;
6373         unsigned int min_shallow;
6374 
6375         min_shallow = bfq_update_depths(bfqd, &tags->bitmap_tags);
6376         sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, min_shallow);
6377 }
6378 
6379 static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
6380 {
6381         bfq_depth_updated(hctx);
6382         return 0;
6383 }
6384 
6385 static void bfq_exit_queue(struct elevator_queue *e)
6386 {
6387         struct bfq_data *bfqd = e->elevator_data;
6388         struct bfq_queue *bfqq, *n;
6389 
6390         hrtimer_cancel(&bfqd->idle_slice_timer);
6391 
6392         spin_lock_irq(&bfqd->lock);
6393         list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
6394                 bfq_deactivate_bfqq(bfqd, bfqq, false, false);
6395         spin_unlock_irq(&bfqd->lock);
6396 
6397         hrtimer_cancel(&bfqd->idle_slice_timer);
6398 
6399         /* release oom-queue reference to root group */
6400         bfqg_and_blkg_put(bfqd->root_group);
6401 
6402 #ifdef CONFIG_BFQ_GROUP_IOSCHED
6403         blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
6404 #else
6405         spin_lock_irq(&bfqd->lock);
6406         bfq_put_async_queues(bfqd, bfqd->root_group);
6407         kfree(bfqd->root_group);
6408         spin_unlock_irq(&bfqd->lock);
6409 #endif
6410 
6411         kfree(bfqd);
6412 }
6413 
6414 static void bfq_init_root_group(struct bfq_group *root_group,
6415                                 struct bfq_data *bfqd)
6416 {
6417         int i;
6418 
6419 #ifdef CONFIG_BFQ_GROUP_IOSCHED
6420         root_group->entity.parent = NULL;
6421         root_group->my_entity = NULL;
6422         root_group->bfqd = bfqd;
6423 #endif
6424         root_group->rq_pos_tree = RB_ROOT;
6425         for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
6426                 root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
6427         root_group->sched_data.bfq_class_idle_last_service = jiffies;
6428 }
6429 
6430 static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
6431 {
6432         struct bfq_data *bfqd;
6433         struct elevator_queue *eq;
6434 
6435         eq = elevator_alloc(q, e);
6436         if (!eq)
6437                 return -ENOMEM;
6438 
6439         bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
6440         if (!bfqd) {
6441                 kobject_put(&eq->kobj);
6442                 return -ENOMEM;
6443         }
6444         eq->elevator_data = bfqd;
6445 
6446         spin_lock_irq(&q->queue_lock);
6447         q->elevator = eq;
6448         spin_unlock_irq(&q->queue_lock);
6449 
6450         /*
6451          * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
6452          * Grab a permanent reference to it, so that the normal code flow
6453          * will not attempt to free it.
6454          */
6455         bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
6456         bfqd->oom_bfqq.ref++;
6457         bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
6458         bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
6459         bfqd->oom_bfqq.entity.new_weight =
6460                 bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
6461 
6462         /* oom_bfqq does not participate to bursts */
6463         bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
6464 
6465         /*
6466          * Trigger weight initialization, according to ioprio, at the
6467          * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
6468          * class won't be changed any more.
6469          */
6470         bfqd->oom_bfqq.entity.prio_changed = 1;
6471 
6472         bfqd->queue = q;
6473 
6474         INIT_LIST_HEAD(&bfqd->dispatch);
6475 
6476         hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
6477                      HRTIMER_MODE_REL);
6478         bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
6479 
6480         bfqd->queue_weights_tree = RB_ROOT_CACHED;
6481         bfqd->num_groups_with_pending_reqs = 0;
6482 
6483         INIT_LIST_HEAD(&bfqd->active_list);
6484         INIT_LIST_HEAD(&bfqd->idle_list);
6485         INIT_HLIST_HEAD(&bfqd->burst_list);
6486 
6487         bfqd->hw_tag = -1;
6488         bfqd->nonrot_with_queueing = blk_queue_nonrot(bfqd->queue);
6489 
6490         bfqd->bfq_max_budget = bfq_default_max_budget;
6491 
6492         bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
6493         bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
6494         bfqd->bfq_back_max = bfq_back_max;
6495         bfqd->bfq_back_penalty = bfq_back_penalty;
6496         bfqd->bfq_slice_idle = bfq_slice_idle;
6497         bfqd->bfq_timeout = bfq_timeout;
6498 
6499         bfqd->bfq_requests_within_timer = 120;
6500 
6501         bfqd->bfq_large_burst_thresh = 8;
6502         bfqd->bfq_burst_interval = msecs_to_jiffies(180);
6503 
6504         bfqd->low_latency = true;
6505 
6506         /*
6507          * Trade-off between responsiveness and fairness.
6508          */
6509         bfqd->bfq_wr_coeff = 30;
6510         bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
6511         bfqd->bfq_wr_max_time = 0;
6512         bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
6513         bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500);
6514         bfqd->bfq_wr_max_softrt_rate = 7000; /*
6515                                               * Approximate rate required
6516                                               * to playback or record a
6517                                               * high-definition compressed
6518                                               * video.
6519                                               */
6520         bfqd->wr_busy_queues = 0;
6521 
6522         /*
6523          * Begin by assuming, optimistically, that the device peak
6524          * rate is equal to 2/3 of the highest reference rate.
6525          */
6526         bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] *
6527                 ref_wr_duration[blk_queue_nonrot(bfqd->queue)];
6528         bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
6529 
6530         spin_lock_init(&bfqd->lock);
6531 
6532         /*
6533          * The invocation of the next bfq_create_group_hierarchy
6534          * function is the head of a chain of function calls
6535          * (bfq_create_group_hierarchy->blkcg_activate_policy->
6536          * blk_mq_freeze_queue) that may lead to the invocation of the
6537          * has_work hook function. For this reason,
6538          * bfq_create_group_hierarchy is invoked only after all
6539          * scheduler data has been initialized, apart from the fields
6540          * that can be initialized only after invoking
6541          * bfq_create_group_hierarchy. This, in particular, enables
6542          * has_work to correctly return false. Of course, to avoid
6543          * other inconsistencies, the blk-mq stack must then refrain
6544          * from invoking further scheduler hooks before this init
6545          * function is finished.
6546          */
6547         bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
6548         if (!bfqd->root_group)
6549                 goto out_free;
6550         bfq_init_root_group(bfqd->root_group, bfqd);
6551         bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
6552 
6553         wbt_disable_default(q);
6554         return 0;
6555 
6556 out_free:
6557         kfree(bfqd);
6558         kobject_put(&eq->kobj);
6559         return -ENOMEM;
6560 }
6561 
6562 static void bfq_slab_kill(void)
6563 {
6564         kmem_cache_destroy(bfq_pool);
6565 }
6566 
6567 static int __init bfq_slab_setup(void)
6568 {
6569         bfq_pool = KMEM_CACHE(bfq_queue, 0);
6570         if (!bfq_pool)
6571                 return -ENOMEM;
6572         return 0;
6573 }
6574 
6575 static ssize_t bfq_var_show(unsigned int var, char *page)
6576 {
6577         return sprintf(page, "%u\n", var);
6578 }
6579 
6580 static int bfq_var_store(unsigned long *var, const char *page)
6581 {
6582         unsigned long new_val;
6583         int ret = kstrtoul(page, 10, &new_val);
6584 
6585         if (ret)
6586                 return ret;
6587         *var = new_val;
6588         return 0;
6589 }
6590 
6591 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
6592 static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
6593 {                                                                       \
6594         struct bfq_data *bfqd = e->elevator_data;                       \
6595         u64 __data = __VAR;                                             \
6596         if (__CONV == 1)                                                \
6597                 __data = jiffies_to_msecs(__data);                      \
6598         else if (__CONV == 2)                                           \
6599                 __data = div_u64(__data, NSEC_PER_MSEC);                \
6600         return bfq_var_show(__data, (page));                            \
6601 }
6602 SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
6603 SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
6604 SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
6605 SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
6606 SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
6607 SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
6608 SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
6609 SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
6610 SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
6611 #undef SHOW_FUNCTION
6612 
6613 #define USEC_SHOW_FUNCTION(__FUNC, __VAR)                               \
6614 static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
6615 {                                                                       \
6616         struct bfq_data *bfqd = e->elevator_data;                       \
6617         u64 __data = __VAR;                                             \
6618         __data = div_u64(__data, NSEC_PER_USEC);                        \
6619         return bfq_var_show(__data, (page));                            \
6620 }
6621 USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
6622 #undef USEC_SHOW_FUNCTION
6623 
6624 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
6625 static ssize_t                                                          \
6626 __FUNC(struct elevator_queue *e, const char *page, size_t count)        \
6627 {                                                                       \
6628         struct bfq_data *bfqd = e->elevator_data;                       \
6629         unsigned long __data, __min = (MIN), __max = (MAX);             \
6630         int ret;                                                        \
6631                                                                         \
6632         ret = bfq_var_store(&__data, (page));                           \
6633         if (ret)                                                        \
6634                 return ret;                                             \
6635         if (__data < __min)                                             \
6636                 __data = __min;                                         \
6637         else if (__data > __max)                                        \
6638                 __data = __max;                                         \
6639         if (__CONV == 1)                                                \
6640                 *(__PTR) = msecs_to_jiffies(__data);                    \
6641         else if (__CONV == 2)                                           \
6642                 *(__PTR) = (u64)__data * NSEC_PER_MSEC;                 \
6643         else                                                            \
6644                 *(__PTR) = __data;                                      \
6645         return count;                                                   \
6646 }
6647 STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
6648                 INT_MAX, 2);
6649 STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
6650                 INT_MAX, 2);
6651 STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
6652 STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
6653                 INT_MAX, 0);
6654 STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
6655 #undef STORE_FUNCTION
6656 
6657 #define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX)                    \
6658 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
6659 {                                                                       \
6660         struct bfq_data *bfqd = e->elevator_data;                       \
6661         unsigned long __data, __min = (MIN), __max = (MAX);             \
6662         int ret;                                                        \
6663                                                                         \
6664         ret = bfq_var_store(&__data, (page));                           \
6665         if (ret)                                                        \
6666                 return ret;                                             \
6667         if (__data < __min)                                             \
6668                 __data = __min;                                         \
6669         else if (__data > __max)                                        \
6670                 __data = __max;                                         \
6671         *(__PTR) = (u64)__data * NSEC_PER_USEC;                         \
6672         return count;                                                   \
6673 }
6674 USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
6675                     UINT_MAX);
6676 #undef USEC_STORE_FUNCTION
6677 
6678 static ssize_t bfq_max_budget_store(struct elevator_queue *e,
6679                                     const char *page, size_t count)
6680 {
6681         struct bfq_data *bfqd = e->elevator_data;
6682         unsigned long __data;
6683         int ret;
6684 
6685         ret = bfq_var_store(&__data, (page));
6686         if (ret)
6687                 return ret;
6688 
6689         if (__data == 0)
6690                 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
6691         else {
6692                 if (__data > INT_MAX)
6693                         __data = INT_MAX;
6694                 bfqd->bfq_max_budget = __data;
6695         }
6696 
6697         bfqd->bfq_user_max_budget = __data;
6698 
6699         return count;
6700 }
6701 
6702 /*
6703  * Leaving this name to preserve name compatibility with cfq
6704  * parameters, but this timeout is used for both sync and async.
6705  */
6706 static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
6707                                       const char *page, size_t count)
6708 {
6709         struct bfq_data *bfqd = e->elevator_data;
6710         unsigned long __data;
6711         int ret;
6712 
6713         ret = bfq_var_store(&__data, (page));
6714         if (ret)
6715                 return ret;
6716 
6717         if (__data < 1)
6718                 __data = 1;
6719         else if (__data > INT_MAX)
6720                 __data = INT_MAX;
6721 
6722         bfqd->bfq_timeout = msecs_to_jiffies(__data);
6723         if (bfqd->bfq_user_max_budget == 0)
6724                 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
6725 
6726         return count;
6727 }
6728 
6729 static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
6730                                      const char *page, size_t count)
6731 {
6732         struct bfq_data *bfqd = e->elevator_data;
6733         unsigned long __data;
6734         int ret;
6735 
6736         ret = bfq_var_store(&__data, (page));
6737         if (ret)
6738                 return ret;
6739 
6740         if (__data > 1)
6741                 __data = 1;
6742         if (!bfqd->strict_guarantees && __data == 1
6743             && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
6744                 bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
6745 
6746         bfqd->strict_guarantees = __data;
6747 
6748         return count;
6749 }
6750 
6751 static ssize_t bfq_low_latency_store(struct elevator_queue *e,
6752                                      const char *page, size_t count)
6753 {
6754         struct bfq_data *bfqd = e->elevator_data;
6755         unsigned long __data;
6756         int ret;
6757 
6758         ret = bfq_var_store(&__data, (page));
6759         if (ret)
6760                 return ret;
6761 
6762         if (__data > 1)
6763                 __data = 1;
6764         if (__data == 0 && bfqd->low_latency != 0)
6765                 bfq_end_wr(bfqd);
6766         bfqd->low_latency = __data;
6767 
6768         return count;
6769 }
6770 
6771 #define BFQ_ATTR(name) \
6772         __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
6773 
6774 static struct elv_fs_entry bfq_attrs[] = {
6775         BFQ_ATTR(fifo_expire_sync),
6776         BFQ_ATTR(fifo_expire_async),
6777         BFQ_ATTR(back_seek_max),
6778         BFQ_ATTR(back_seek_penalty),
6779         BFQ_ATTR(slice_idle),
6780         BFQ_ATTR(slice_idle_us),
6781         BFQ_ATTR(max_budget),
6782         BFQ_ATTR(timeout_sync),
6783         BFQ_ATTR(strict_guarantees),
6784         BFQ_ATTR(low_latency),
6785         __ATTR_NULL
6786 };
6787 
6788 static struct elevator_type iosched_bfq_mq = {
6789         .ops = {
6790                 .limit_depth            = bfq_limit_depth,
6791                 .prepare_request        = bfq_prepare_request,
6792                 .requeue_request        = bfq_finish_requeue_request,
6793                 .finish_request         = bfq_finish_requeue_request,
6794                 .exit_icq               = bfq_exit_icq,
6795                 .insert_requests        = bfq_insert_requests,
6796                 .dispatch_request       = bfq_dispatch_request,
6797                 .next_request           = elv_rb_latter_request,
6798                 .former_request         = elv_rb_former_request,
6799                 .allow_merge            = bfq_allow_bio_merge,
6800                 .bio_merge              = bfq_bio_merge,
6801                 .request_merge          = bfq_request_merge,
6802                 .requests_merged        = bfq_requests_merged,
6803                 .request_merged         = bfq_request_merged,
6804                 .has_work               = bfq_has_work,
6805                 .depth_updated          = bfq_depth_updated,
6806                 .init_hctx              = bfq_init_hctx,
6807                 .init_sched             = bfq_init_queue,
6808                 .exit_sched             = bfq_exit_queue,
6809         },
6810 
6811         .icq_size =             sizeof(struct bfq_io_cq),
6812         .icq_align =            __alignof__(struct bfq_io_cq),
6813         .elevator_attrs =       bfq_attrs,
6814         .elevator_name =        "bfq",
6815         .elevator_owner =       THIS_MODULE,
6816 };
6817 MODULE_ALIAS("bfq-iosched");
6818 
6819 static int __init bfq_init(void)
6820 {
6821         int ret;
6822 
6823 #ifdef CONFIG_BFQ_GROUP_IOSCHED
6824         ret = blkcg_policy_register(&blkcg_policy_bfq);
6825         if (ret)
6826                 return ret;
6827 #endif
6828 
6829         ret = -ENOMEM;
6830         if (bfq_slab_setup())
6831                 goto err_pol_unreg;
6832 
6833         /*
6834          * Times to load large popular applications for the typical
6835          * systems installed on the reference devices (see the
6836          * comments before the definition of the next
6837          * array). Actually, we use slightly lower values, as the
6838          * estimated peak rate tends to be smaller than the actual
6839          * peak rate.  The reason for this last fact is that estimates
6840          * are computed over much shorter time intervals than the long
6841          * intervals typically used for benchmarking. Why? First, to
6842          * adapt more quickly to variations. Second, because an I/O
6843          * scheduler cannot rely on a peak-rate-evaluation workload to
6844          * be run for a long time.
6845          */
6846         ref_wr_duration[0] = msecs_to_jiffies(7000); /* actually 8 sec */
6847         ref_wr_duration[1] = msecs_to_jiffies(2500); /* actually 3 sec */
6848 
6849         ret = elv_register(&iosched_bfq_mq);
6850         if (ret)
6851                 goto slab_kill;
6852 
6853         return 0;
6854 
6855 slab_kill:
6856         bfq_slab_kill();
6857 err_pol_unreg:
6858 #ifdef CONFIG_BFQ_GROUP_IOSCHED
6859         blkcg_policy_unregister(&blkcg_policy_bfq);
6860 #endif
6861         return ret;
6862 }
6863 
6864 static void __exit bfq_exit(void)
6865 {
6866         elv_unregister(&iosched_bfq_mq);
6867 #ifdef CONFIG_BFQ_GROUP_IOSCHED
6868         blkcg_policy_unregister(&blkcg_policy_bfq);
6869 #endif
6870         bfq_slab_kill();
6871 }
6872 
6873 module_init(bfq_init);
6874 module_exit(bfq_exit);
6875 
6876 MODULE_AUTHOR("Paolo Valente");
6877 MODULE_LICENSE("GPL");
6878 MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");
6879 

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