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TOMOYO Linux Cross Reference
Linux/block/cfq-iosched.c

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  1 /*
  2  *  CFQ, or complete fairness queueing, disk scheduler.
  3  *
  4  *  Based on ideas from a previously unfinished io
  5  *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
  6  *
  7  *  Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
  8  */
  9 #include <linux/module.h>
 10 #include <linux/slab.h>
 11 #include <linux/blkdev.h>
 12 #include <linux/elevator.h>
 13 #include <linux/jiffies.h>
 14 #include <linux/rbtree.h>
 15 #include <linux/ioprio.h>
 16 #include <linux/blktrace_api.h>
 17 #include "cfq.h"
 18 
 19 /*
 20  * tunables
 21  */
 22 /* max queue in one round of service */
 23 static const int cfq_quantum = 8;
 24 static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
 25 /* maximum backwards seek, in KiB */
 26 static const int cfq_back_max = 16 * 1024;
 27 /* penalty of a backwards seek */
 28 static const int cfq_back_penalty = 2;
 29 static const int cfq_slice_sync = HZ / 10;
 30 static int cfq_slice_async = HZ / 25;
 31 static const int cfq_slice_async_rq = 2;
 32 static int cfq_slice_idle = HZ / 125;
 33 static int cfq_group_idle = HZ / 125;
 34 static const int cfq_target_latency = HZ * 3/10; /* 300 ms */
 35 static const int cfq_hist_divisor = 4;
 36 
 37 /*
 38  * offset from end of service tree
 39  */
 40 #define CFQ_IDLE_DELAY          (HZ / 5)
 41 
 42 /*
 43  * below this threshold, we consider thinktime immediate
 44  */
 45 #define CFQ_MIN_TT              (2)
 46 
 47 #define CFQ_SLICE_SCALE         (5)
 48 #define CFQ_HW_QUEUE_MIN        (5)
 49 #define CFQ_SERVICE_SHIFT       12
 50 
 51 #define CFQQ_SEEK_THR           (sector_t)(8 * 100)
 52 #define CFQQ_CLOSE_THR          (sector_t)(8 * 1024)
 53 #define CFQQ_SECT_THR_NONROT    (sector_t)(2 * 32)
 54 #define CFQQ_SEEKY(cfqq)        (hweight32(cfqq->seek_history) > 32/8)
 55 
 56 #define RQ_CIC(rq)              \
 57         ((struct cfq_io_context *) (rq)->elevator_private[0])
 58 #define RQ_CFQQ(rq)             (struct cfq_queue *) ((rq)->elevator_private[1])
 59 #define RQ_CFQG(rq)             (struct cfq_group *) ((rq)->elevator_private[2])
 60 
 61 static struct kmem_cache *cfq_pool;
 62 static struct kmem_cache *cfq_ioc_pool;
 63 
 64 static DEFINE_PER_CPU(unsigned long, cfq_ioc_count);
 65 static struct completion *ioc_gone;
 66 static DEFINE_SPINLOCK(ioc_gone_lock);
 67 
 68 static DEFINE_SPINLOCK(cic_index_lock);
 69 static DEFINE_IDA(cic_index_ida);
 70 
 71 #define CFQ_PRIO_LISTS          IOPRIO_BE_NR
 72 #define cfq_class_idle(cfqq)    ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
 73 #define cfq_class_rt(cfqq)      ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)
 74 
 75 #define sample_valid(samples)   ((samples) > 80)
 76 #define rb_entry_cfqg(node)     rb_entry((node), struct cfq_group, rb_node)
 77 
 78 /*
 79  * Most of our rbtree usage is for sorting with min extraction, so
 80  * if we cache the leftmost node we don't have to walk down the tree
 81  * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
 82  * move this into the elevator for the rq sorting as well.
 83  */
 84 struct cfq_rb_root {
 85         struct rb_root rb;
 86         struct rb_node *left;
 87         unsigned count;
 88         unsigned total_weight;
 89         u64 min_vdisktime;
 90 };
 91 #define CFQ_RB_ROOT     (struct cfq_rb_root) { .rb = RB_ROOT, .left = NULL, \
 92                         .count = 0, .min_vdisktime = 0, }
 93 
 94 /*
 95  * Per process-grouping structure
 96  */
 97 struct cfq_queue {
 98         /* reference count */
 99         int ref;
100         /* various state flags, see below */
101         unsigned int flags;
102         /* parent cfq_data */
103         struct cfq_data *cfqd;
104         /* service_tree member */
105         struct rb_node rb_node;
106         /* service_tree key */
107         unsigned long rb_key;
108         /* prio tree member */
109         struct rb_node p_node;
110         /* prio tree root we belong to, if any */
111         struct rb_root *p_root;
112         /* sorted list of pending requests */
113         struct rb_root sort_list;
114         /* if fifo isn't expired, next request to serve */
115         struct request *next_rq;
116         /* requests queued in sort_list */
117         int queued[2];
118         /* currently allocated requests */
119         int allocated[2];
120         /* fifo list of requests in sort_list */
121         struct list_head fifo;
122 
123         /* time when queue got scheduled in to dispatch first request. */
124         unsigned long dispatch_start;
125         unsigned int allocated_slice;
126         unsigned int slice_dispatch;
127         /* time when first request from queue completed and slice started. */
128         unsigned long slice_start;
129         unsigned long slice_end;
130         long slice_resid;
131 
132         /* pending metadata requests */
133         int meta_pending;
134         /* number of requests that are on the dispatch list or inside driver */
135         int dispatched;
136 
137         /* io prio of this group */
138         unsigned short ioprio, org_ioprio;
139         unsigned short ioprio_class, org_ioprio_class;
140 
141         pid_t pid;
142 
143         u32 seek_history;
144         sector_t last_request_pos;
145 
146         struct cfq_rb_root *service_tree;
147         struct cfq_queue *new_cfqq;
148         struct cfq_group *cfqg;
149         /* Number of sectors dispatched from queue in single dispatch round */
150         unsigned long nr_sectors;
151 };
152 
153 /*
154  * First index in the service_trees.
155  * IDLE is handled separately, so it has negative index
156  */
157 enum wl_prio_t {
158         BE_WORKLOAD = 0,
159         RT_WORKLOAD = 1,
160         IDLE_WORKLOAD = 2,
161         CFQ_PRIO_NR,
162 };
163 
164 /*
165  * Second index in the service_trees.
166  */
167 enum wl_type_t {
168         ASYNC_WORKLOAD = 0,
169         SYNC_NOIDLE_WORKLOAD = 1,
170         SYNC_WORKLOAD = 2
171 };
172 
173 /* This is per cgroup per device grouping structure */
174 struct cfq_group {
175         /* group service_tree member */
176         struct rb_node rb_node;
177 
178         /* group service_tree key */
179         u64 vdisktime;
180         unsigned int weight;
181         unsigned int new_weight;
182         bool needs_update;
183 
184         /* number of cfqq currently on this group */
185         int nr_cfqq;
186 
187         /*
188          * Per group busy queues average. Useful for workload slice calc. We
189          * create the array for each prio class but at run time it is used
190          * only for RT and BE class and slot for IDLE class remains unused.
191          * This is primarily done to avoid confusion and a gcc warning.
192          */
193         unsigned int busy_queues_avg[CFQ_PRIO_NR];
194         /*
195          * rr lists of queues with requests. We maintain service trees for
196          * RT and BE classes. These trees are subdivided in subclasses
197          * of SYNC, SYNC_NOIDLE and ASYNC based on workload type. For IDLE
198          * class there is no subclassification and all the cfq queues go on
199          * a single tree service_tree_idle.
200          * Counts are embedded in the cfq_rb_root
201          */
202         struct cfq_rb_root service_trees[2][3];
203         struct cfq_rb_root service_tree_idle;
204 
205         unsigned long saved_workload_slice;
206         enum wl_type_t saved_workload;
207         enum wl_prio_t saved_serving_prio;
208         struct blkio_group blkg;
209 #ifdef CONFIG_CFQ_GROUP_IOSCHED
210         struct hlist_node cfqd_node;
211         int ref;
212 #endif
213         /* number of requests that are on the dispatch list or inside driver */
214         int dispatched;
215 };
216 
217 /*
218  * Per block device queue structure
219  */
220 struct cfq_data {
221         struct request_queue *queue;
222         /* Root service tree for cfq_groups */
223         struct cfq_rb_root grp_service_tree;
224         struct cfq_group root_group;
225 
226         /*
227          * The priority currently being served
228          */
229         enum wl_prio_t serving_prio;
230         enum wl_type_t serving_type;
231         unsigned long workload_expires;
232         struct cfq_group *serving_group;
233 
234         /*
235          * Each priority tree is sorted by next_request position.  These
236          * trees are used when determining if two or more queues are
237          * interleaving requests (see cfq_close_cooperator).
238          */
239         struct rb_root prio_trees[CFQ_PRIO_LISTS];
240 
241         unsigned int busy_queues;
242         unsigned int busy_sync_queues;
243 
244         int rq_in_driver;
245         int rq_in_flight[2];
246 
247         /*
248          * queue-depth detection
249          */
250         int rq_queued;
251         int hw_tag;
252         /*
253          * hw_tag can be
254          * -1 => indeterminate, (cfq will behave as if NCQ is present, to allow better detection)
255          *  1 => NCQ is present (hw_tag_est_depth is the estimated max depth)
256          *  0 => no NCQ
257          */
258         int hw_tag_est_depth;
259         unsigned int hw_tag_samples;
260 
261         /*
262          * idle window management
263          */
264         struct timer_list idle_slice_timer;
265         struct work_struct unplug_work;
266 
267         struct cfq_queue *active_queue;
268         struct cfq_io_context *active_cic;
269 
270         /*
271          * async queue for each priority case
272          */
273         struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
274         struct cfq_queue *async_idle_cfqq;
275 
276         sector_t last_position;
277 
278         /*
279          * tunables, see top of file
280          */
281         unsigned int cfq_quantum;
282         unsigned int cfq_fifo_expire[2];
283         unsigned int cfq_back_penalty;
284         unsigned int cfq_back_max;
285         unsigned int cfq_slice[2];
286         unsigned int cfq_slice_async_rq;
287         unsigned int cfq_slice_idle;
288         unsigned int cfq_group_idle;
289         unsigned int cfq_latency;
290 
291         unsigned int cic_index;
292         struct list_head cic_list;
293 
294         /*
295          * Fallback dummy cfqq for extreme OOM conditions
296          */
297         struct cfq_queue oom_cfqq;
298 
299         unsigned long last_delayed_sync;
300 
301         /* List of cfq groups being managed on this device*/
302         struct hlist_head cfqg_list;
303 
304         /* Number of groups which are on blkcg->blkg_list */
305         unsigned int nr_blkcg_linked_grps;
306 };
307 
308 static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd);
309 
310 static struct cfq_rb_root *service_tree_for(struct cfq_group *cfqg,
311                                             enum wl_prio_t prio,
312                                             enum wl_type_t type)
313 {
314         if (!cfqg)
315                 return NULL;
316 
317         if (prio == IDLE_WORKLOAD)
318                 return &cfqg->service_tree_idle;
319 
320         return &cfqg->service_trees[prio][type];
321 }
322 
323 enum cfqq_state_flags {
324         CFQ_CFQQ_FLAG_on_rr = 0,        /* on round-robin busy list */
325         CFQ_CFQQ_FLAG_wait_request,     /* waiting for a request */
326         CFQ_CFQQ_FLAG_must_dispatch,    /* must be allowed a dispatch */
327         CFQ_CFQQ_FLAG_must_alloc_slice, /* per-slice must_alloc flag */
328         CFQ_CFQQ_FLAG_fifo_expire,      /* FIFO checked in this slice */
329         CFQ_CFQQ_FLAG_idle_window,      /* slice idling enabled */
330         CFQ_CFQQ_FLAG_prio_changed,     /* task priority has changed */
331         CFQ_CFQQ_FLAG_slice_new,        /* no requests dispatched in slice */
332         CFQ_CFQQ_FLAG_sync,             /* synchronous queue */
333         CFQ_CFQQ_FLAG_coop,             /* cfqq is shared */
334         CFQ_CFQQ_FLAG_split_coop,       /* shared cfqq will be splitted */
335         CFQ_CFQQ_FLAG_deep,             /* sync cfqq experienced large depth */
336         CFQ_CFQQ_FLAG_wait_busy,        /* Waiting for next request */
337 };
338 
339 #define CFQ_CFQQ_FNS(name)                                              \
340 static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)         \
341 {                                                                       \
342         (cfqq)->flags |= (1 << CFQ_CFQQ_FLAG_##name);                   \
343 }                                                                       \
344 static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)        \
345 {                                                                       \
346         (cfqq)->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);                  \
347 }                                                                       \
348 static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)         \
349 {                                                                       \
350         return ((cfqq)->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;      \
351 }
352 
353 CFQ_CFQQ_FNS(on_rr);
354 CFQ_CFQQ_FNS(wait_request);
355 CFQ_CFQQ_FNS(must_dispatch);
356 CFQ_CFQQ_FNS(must_alloc_slice);
357 CFQ_CFQQ_FNS(fifo_expire);
358 CFQ_CFQQ_FNS(idle_window);
359 CFQ_CFQQ_FNS(prio_changed);
360 CFQ_CFQQ_FNS(slice_new);
361 CFQ_CFQQ_FNS(sync);
362 CFQ_CFQQ_FNS(coop);
363 CFQ_CFQQ_FNS(split_coop);
364 CFQ_CFQQ_FNS(deep);
365 CFQ_CFQQ_FNS(wait_busy);
366 #undef CFQ_CFQQ_FNS
367 
368 #ifdef CONFIG_CFQ_GROUP_IOSCHED
369 #define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  \
370         blk_add_trace_msg((cfqd)->queue, "cfq%d%c %s " fmt, (cfqq)->pid, \
371                         cfq_cfqq_sync((cfqq)) ? 'S' : 'A', \
372                         blkg_path(&(cfqq)->cfqg->blkg), ##args)
373 
374 #define cfq_log_cfqg(cfqd, cfqg, fmt, args...)                          \
375         blk_add_trace_msg((cfqd)->queue, "%s " fmt,                     \
376                                 blkg_path(&(cfqg)->blkg), ##args)       \
377 
378 #else
379 #define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  \
380         blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)
381 #define cfq_log_cfqg(cfqd, cfqg, fmt, args...)          do {} while (0)
382 #endif
383 #define cfq_log(cfqd, fmt, args...)     \
384         blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)
385 
386 /* Traverses through cfq group service trees */
387 #define for_each_cfqg_st(cfqg, i, j, st) \
388         for (i = 0; i <= IDLE_WORKLOAD; i++) \
389                 for (j = 0, st = i < IDLE_WORKLOAD ? &cfqg->service_trees[i][j]\
390                         : &cfqg->service_tree_idle; \
391                         (i < IDLE_WORKLOAD && j <= SYNC_WORKLOAD) || \
392                         (i == IDLE_WORKLOAD && j == 0); \
393                         j++, st = i < IDLE_WORKLOAD ? \
394                         &cfqg->service_trees[i][j]: NULL) \
395 
396 
397 static inline bool iops_mode(struct cfq_data *cfqd)
398 {
399         /*
400          * If we are not idling on queues and it is a NCQ drive, parallel
401          * execution of requests is on and measuring time is not possible
402          * in most of the cases until and unless we drive shallower queue
403          * depths and that becomes a performance bottleneck. In such cases
404          * switch to start providing fairness in terms of number of IOs.
405          */
406         if (!cfqd->cfq_slice_idle && cfqd->hw_tag)
407                 return true;
408         else
409                 return false;
410 }
411 
412 static inline enum wl_prio_t cfqq_prio(struct cfq_queue *cfqq)
413 {
414         if (cfq_class_idle(cfqq))
415                 return IDLE_WORKLOAD;
416         if (cfq_class_rt(cfqq))
417                 return RT_WORKLOAD;
418         return BE_WORKLOAD;
419 }
420 
421 
422 static enum wl_type_t cfqq_type(struct cfq_queue *cfqq)
423 {
424         if (!cfq_cfqq_sync(cfqq))
425                 return ASYNC_WORKLOAD;
426         if (!cfq_cfqq_idle_window(cfqq))
427                 return SYNC_NOIDLE_WORKLOAD;
428         return SYNC_WORKLOAD;
429 }
430 
431 static inline int cfq_group_busy_queues_wl(enum wl_prio_t wl,
432                                         struct cfq_data *cfqd,
433                                         struct cfq_group *cfqg)
434 {
435         if (wl == IDLE_WORKLOAD)
436                 return cfqg->service_tree_idle.count;
437 
438         return cfqg->service_trees[wl][ASYNC_WORKLOAD].count
439                 + cfqg->service_trees[wl][SYNC_NOIDLE_WORKLOAD].count
440                 + cfqg->service_trees[wl][SYNC_WORKLOAD].count;
441 }
442 
443 static inline int cfqg_busy_async_queues(struct cfq_data *cfqd,
444                                         struct cfq_group *cfqg)
445 {
446         return cfqg->service_trees[RT_WORKLOAD][ASYNC_WORKLOAD].count
447                 + cfqg->service_trees[BE_WORKLOAD][ASYNC_WORKLOAD].count;
448 }
449 
450 static void cfq_dispatch_insert(struct request_queue *, struct request *);
451 static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,
452                                        struct io_context *, gfp_t);
453 static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,
454                                                 struct io_context *);
455 
456 static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,
457                                             bool is_sync)
458 {
459         return cic->cfqq[is_sync];
460 }
461 
462 static inline void cic_set_cfqq(struct cfq_io_context *cic,
463                                 struct cfq_queue *cfqq, bool is_sync)
464 {
465         cic->cfqq[is_sync] = cfqq;
466 }
467 
468 #define CIC_DEAD_KEY    1ul
469 #define CIC_DEAD_INDEX_SHIFT    1
470 
471 static inline void *cfqd_dead_key(struct cfq_data *cfqd)
472 {
473         return (void *)(cfqd->cic_index << CIC_DEAD_INDEX_SHIFT | CIC_DEAD_KEY);
474 }
475 
476 static inline struct cfq_data *cic_to_cfqd(struct cfq_io_context *cic)
477 {
478         struct cfq_data *cfqd = cic->key;
479 
480         if (unlikely((unsigned long) cfqd & CIC_DEAD_KEY))
481                 return NULL;
482 
483         return cfqd;
484 }
485 
486 /*
487  * We regard a request as SYNC, if it's either a read or has the SYNC bit
488  * set (in which case it could also be direct WRITE).
489  */
490 static inline bool cfq_bio_sync(struct bio *bio)
491 {
492         return bio_data_dir(bio) == READ || (bio->bi_rw & REQ_SYNC);
493 }
494 
495 /*
496  * scheduler run of queue, if there are requests pending and no one in the
497  * driver that will restart queueing
498  */
499 static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
500 {
501         if (cfqd->busy_queues) {
502                 cfq_log(cfqd, "schedule dispatch");
503                 kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);
504         }
505 }
506 
507 /*
508  * Scale schedule slice based on io priority. Use the sync time slice only
509  * if a queue is marked sync and has sync io queued. A sync queue with async
510  * io only, should not get full sync slice length.
511  */
512 static inline int cfq_prio_slice(struct cfq_data *cfqd, bool sync,
513                                  unsigned short prio)
514 {
515         const int base_slice = cfqd->cfq_slice[sync];
516 
517         WARN_ON(prio >= IOPRIO_BE_NR);
518 
519         return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
520 }
521 
522 static inline int
523 cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
524 {
525         return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
526 }
527 
528 static inline u64 cfq_scale_slice(unsigned long delta, struct cfq_group *cfqg)
529 {
530         u64 d = delta << CFQ_SERVICE_SHIFT;
531 
532         d = d * BLKIO_WEIGHT_DEFAULT;
533         do_div(d, cfqg->weight);
534         return d;
535 }
536 
537 static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime)
538 {
539         s64 delta = (s64)(vdisktime - min_vdisktime);
540         if (delta > 0)
541                 min_vdisktime = vdisktime;
542 
543         return min_vdisktime;
544 }
545 
546 static inline u64 min_vdisktime(u64 min_vdisktime, u64 vdisktime)
547 {
548         s64 delta = (s64)(vdisktime - min_vdisktime);
549         if (delta < 0)
550                 min_vdisktime = vdisktime;
551 
552         return min_vdisktime;
553 }
554 
555 static void update_min_vdisktime(struct cfq_rb_root *st)
556 {
557         struct cfq_group *cfqg;
558 
559         if (st->left) {
560                 cfqg = rb_entry_cfqg(st->left);
561                 st->min_vdisktime = max_vdisktime(st->min_vdisktime,
562                                                   cfqg->vdisktime);
563         }
564 }
565 
566 /*
567  * get averaged number of queues of RT/BE priority.
568  * average is updated, with a formula that gives more weight to higher numbers,
569  * to quickly follows sudden increases and decrease slowly
570  */
571 
572 static inline unsigned cfq_group_get_avg_queues(struct cfq_data *cfqd,
573                                         struct cfq_group *cfqg, bool rt)
574 {
575         unsigned min_q, max_q;
576         unsigned mult  = cfq_hist_divisor - 1;
577         unsigned round = cfq_hist_divisor / 2;
578         unsigned busy = cfq_group_busy_queues_wl(rt, cfqd, cfqg);
579 
580         min_q = min(cfqg->busy_queues_avg[rt], busy);
581         max_q = max(cfqg->busy_queues_avg[rt], busy);
582         cfqg->busy_queues_avg[rt] = (mult * max_q + min_q + round) /
583                 cfq_hist_divisor;
584         return cfqg->busy_queues_avg[rt];
585 }
586 
587 static inline unsigned
588 cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg)
589 {
590         struct cfq_rb_root *st = &cfqd->grp_service_tree;
591 
592         return cfq_target_latency * cfqg->weight / st->total_weight;
593 }
594 
595 static inline unsigned
596 cfq_scaled_cfqq_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
597 {
598         unsigned slice = cfq_prio_to_slice(cfqd, cfqq);
599         if (cfqd->cfq_latency) {
600                 /*
601                  * interested queues (we consider only the ones with the same
602                  * priority class in the cfq group)
603                  */
604                 unsigned iq = cfq_group_get_avg_queues(cfqd, cfqq->cfqg,
605                                                 cfq_class_rt(cfqq));
606                 unsigned sync_slice = cfqd->cfq_slice[1];
607                 unsigned expect_latency = sync_slice * iq;
608                 unsigned group_slice = cfq_group_slice(cfqd, cfqq->cfqg);
609 
610                 if (expect_latency > group_slice) {
611                         unsigned base_low_slice = 2 * cfqd->cfq_slice_idle;
612                         /* scale low_slice according to IO priority
613                          * and sync vs async */
614                         unsigned low_slice =
615                                 min(slice, base_low_slice * slice / sync_slice);
616                         /* the adapted slice value is scaled to fit all iqs
617                          * into the target latency */
618                         slice = max(slice * group_slice / expect_latency,
619                                     low_slice);
620                 }
621         }
622         return slice;
623 }
624 
625 static inline void
626 cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
627 {
628         unsigned slice = cfq_scaled_cfqq_slice(cfqd, cfqq);
629 
630         cfqq->slice_start = jiffies;
631         cfqq->slice_end = jiffies + slice;
632         cfqq->allocated_slice = slice;
633         cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);
634 }
635 
636 /*
637  * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
638  * isn't valid until the first request from the dispatch is activated
639  * and the slice time set.
640  */
641 static inline bool cfq_slice_used(struct cfq_queue *cfqq)
642 {
643         if (cfq_cfqq_slice_new(cfqq))
644                 return false;
645         if (time_before(jiffies, cfqq->slice_end))
646                 return false;
647 
648         return true;
649 }
650 
651 /*
652  * Lifted from AS - choose which of rq1 and rq2 that is best served now.
653  * We choose the request that is closest to the head right now. Distance
654  * behind the head is penalized and only allowed to a certain extent.
655  */
656 static struct request *
657 cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2, sector_t last)
658 {
659         sector_t s1, s2, d1 = 0, d2 = 0;
660         unsigned long back_max;
661 #define CFQ_RQ1_WRAP    0x01 /* request 1 wraps */
662 #define CFQ_RQ2_WRAP    0x02 /* request 2 wraps */
663         unsigned wrap = 0; /* bit mask: requests behind the disk head? */
664 
665         if (rq1 == NULL || rq1 == rq2)
666                 return rq2;
667         if (rq2 == NULL)
668                 return rq1;
669 
670         if (rq_is_sync(rq1) != rq_is_sync(rq2))
671                 return rq_is_sync(rq1) ? rq1 : rq2;
672 
673         if ((rq1->cmd_flags ^ rq2->cmd_flags) & REQ_META)
674                 return rq1->cmd_flags & REQ_META ? rq1 : rq2;
675 
676         s1 = blk_rq_pos(rq1);
677         s2 = blk_rq_pos(rq2);
678 
679         /*
680          * by definition, 1KiB is 2 sectors
681          */
682         back_max = cfqd->cfq_back_max * 2;
683 
684         /*
685          * Strict one way elevator _except_ in the case where we allow
686          * short backward seeks which are biased as twice the cost of a
687          * similar forward seek.
688          */
689         if (s1 >= last)
690                 d1 = s1 - last;
691         else if (s1 + back_max >= last)
692                 d1 = (last - s1) * cfqd->cfq_back_penalty;
693         else
694                 wrap |= CFQ_RQ1_WRAP;
695 
696         if (s2 >= last)
697                 d2 = s2 - last;
698         else if (s2 + back_max >= last)
699                 d2 = (last - s2) * cfqd->cfq_back_penalty;
700         else
701                 wrap |= CFQ_RQ2_WRAP;
702 
703         /* Found required data */
704 
705         /*
706          * By doing switch() on the bit mask "wrap" we avoid having to
707          * check two variables for all permutations: --> faster!
708          */
709         switch (wrap) {
710         case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
711                 if (d1 < d2)
712                         return rq1;
713                 else if (d2 < d1)
714                         return rq2;
715                 else {
716                         if (s1 >= s2)
717                                 return rq1;
718                         else
719                                 return rq2;
720                 }
721 
722         case CFQ_RQ2_WRAP:
723                 return rq1;
724         case CFQ_RQ1_WRAP:
725                 return rq2;
726         case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */
727         default:
728                 /*
729                  * Since both rqs are wrapped,
730                  * start with the one that's further behind head
731                  * (--> only *one* back seek required),
732                  * since back seek takes more time than forward.
733                  */
734                 if (s1 <= s2)
735                         return rq1;
736                 else
737                         return rq2;
738         }
739 }
740 
741 /*
742  * The below is leftmost cache rbtree addon
743  */
744 static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)
745 {
746         /* Service tree is empty */
747         if (!root->count)
748                 return NULL;
749 
750         if (!root->left)
751                 root->left = rb_first(&root->rb);
752 
753         if (root->left)
754                 return rb_entry(root->left, struct cfq_queue, rb_node);
755 
756         return NULL;
757 }
758 
759 static struct cfq_group *cfq_rb_first_group(struct cfq_rb_root *root)
760 {
761         if (!root->left)
762                 root->left = rb_first(&root->rb);
763 
764         if (root->left)
765                 return rb_entry_cfqg(root->left);
766 
767         return NULL;
768 }
769 
770 static void rb_erase_init(struct rb_node *n, struct rb_root *root)
771 {
772         rb_erase(n, root);
773         RB_CLEAR_NODE(n);
774 }
775 
776 static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
777 {
778         if (root->left == n)
779                 root->left = NULL;
780         rb_erase_init(n, &root->rb);
781         --root->count;
782 }
783 
784 /*
785  * would be nice to take fifo expire time into account as well
786  */
787 static struct request *
788 cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
789                   struct request *last)
790 {
791         struct rb_node *rbnext = rb_next(&last->rb_node);
792         struct rb_node *rbprev = rb_prev(&last->rb_node);
793         struct request *next = NULL, *prev = NULL;
794 
795         BUG_ON(RB_EMPTY_NODE(&last->rb_node));
796 
797         if (rbprev)
798                 prev = rb_entry_rq(rbprev);
799 
800         if (rbnext)
801                 next = rb_entry_rq(rbnext);
802         else {
803                 rbnext = rb_first(&cfqq->sort_list);
804                 if (rbnext && rbnext != &last->rb_node)
805                         next = rb_entry_rq(rbnext);
806         }
807 
808         return cfq_choose_req(cfqd, next, prev, blk_rq_pos(last));
809 }
810 
811 static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
812                                       struct cfq_queue *cfqq)
813 {
814         /*
815          * just an approximation, should be ok.
816          */
817         return (cfqq->cfqg->nr_cfqq - 1) * (cfq_prio_slice(cfqd, 1, 0) -
818                        cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));
819 }
820 
821 static inline s64
822 cfqg_key(struct cfq_rb_root *st, struct cfq_group *cfqg)
823 {
824         return cfqg->vdisktime - st->min_vdisktime;
825 }
826 
827 static void
828 __cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
829 {
830         struct rb_node **node = &st->rb.rb_node;
831         struct rb_node *parent = NULL;
832         struct cfq_group *__cfqg;
833         s64 key = cfqg_key(st, cfqg);
834         int left = 1;
835 
836         while (*node != NULL) {
837                 parent = *node;
838                 __cfqg = rb_entry_cfqg(parent);
839 
840                 if (key < cfqg_key(st, __cfqg))
841                         node = &parent->rb_left;
842                 else {
843                         node = &parent->rb_right;
844                         left = 0;
845                 }
846         }
847 
848         if (left)
849                 st->left = &cfqg->rb_node;
850 
851         rb_link_node(&cfqg->rb_node, parent, node);
852         rb_insert_color(&cfqg->rb_node, &st->rb);
853 }
854 
855 static void
856 cfq_update_group_weight(struct cfq_group *cfqg)
857 {
858         BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));
859         if (cfqg->needs_update) {
860                 cfqg->weight = cfqg->new_weight;
861                 cfqg->needs_update = false;
862         }
863 }
864 
865 static void
866 cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
867 {
868         BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));
869 
870         cfq_update_group_weight(cfqg);
871         __cfq_group_service_tree_add(st, cfqg);
872         st->total_weight += cfqg->weight;
873 }
874 
875 static void
876 cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
877 {
878         struct cfq_rb_root *st = &cfqd->grp_service_tree;
879         struct cfq_group *__cfqg;
880         struct rb_node *n;
881 
882         cfqg->nr_cfqq++;
883         if (!RB_EMPTY_NODE(&cfqg->rb_node))
884                 return;
885 
886         /*
887          * Currently put the group at the end. Later implement something
888          * so that groups get lesser vtime based on their weights, so that
889          * if group does not loose all if it was not continuously backlogged.
890          */
891         n = rb_last(&st->rb);
892         if (n) {
893                 __cfqg = rb_entry_cfqg(n);
894                 cfqg->vdisktime = __cfqg->vdisktime + CFQ_IDLE_DELAY;
895         } else
896                 cfqg->vdisktime = st->min_vdisktime;
897         cfq_group_service_tree_add(st, cfqg);
898 }
899 
900 static void
901 cfq_group_service_tree_del(struct cfq_rb_root *st, struct cfq_group *cfqg)
902 {
903         st->total_weight -= cfqg->weight;
904         if (!RB_EMPTY_NODE(&cfqg->rb_node))
905                 cfq_rb_erase(&cfqg->rb_node, st);
906 }
907 
908 static void
909 cfq_group_notify_queue_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
910 {
911         struct cfq_rb_root *st = &cfqd->grp_service_tree;
912 
913         BUG_ON(cfqg->nr_cfqq < 1);
914         cfqg->nr_cfqq--;
915 
916         /* If there are other cfq queues under this group, don't delete it */
917         if (cfqg->nr_cfqq)
918                 return;
919 
920         cfq_log_cfqg(cfqd, cfqg, "del_from_rr group");
921         cfq_group_service_tree_del(st, cfqg);
922         cfqg->saved_workload_slice = 0;
923         cfq_blkiocg_update_dequeue_stats(&cfqg->blkg, 1);
924 }
925 
926 static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq,
927                                                 unsigned int *unaccounted_time)
928 {
929         unsigned int slice_used;
930 
931         /*
932          * Queue got expired before even a single request completed or
933          * got expired immediately after first request completion.
934          */
935         if (!cfqq->slice_start || cfqq->slice_start == jiffies) {
936                 /*
937                  * Also charge the seek time incurred to the group, otherwise
938                  * if there are mutiple queues in the group, each can dispatch
939                  * a single request on seeky media and cause lots of seek time
940                  * and group will never know it.
941                  */
942                 slice_used = max_t(unsigned, (jiffies - cfqq->dispatch_start),
943                                         1);
944         } else {
945                 slice_used = jiffies - cfqq->slice_start;
946                 if (slice_used > cfqq->allocated_slice) {
947                         *unaccounted_time = slice_used - cfqq->allocated_slice;
948                         slice_used = cfqq->allocated_slice;
949                 }
950                 if (time_after(cfqq->slice_start, cfqq->dispatch_start))
951                         *unaccounted_time += cfqq->slice_start -
952                                         cfqq->dispatch_start;
953         }
954 
955         return slice_used;
956 }
957 
958 static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
959                                 struct cfq_queue *cfqq)
960 {
961         struct cfq_rb_root *st = &cfqd->grp_service_tree;
962         unsigned int used_sl, charge, unaccounted_sl = 0;
963         int nr_sync = cfqg->nr_cfqq - cfqg_busy_async_queues(cfqd, cfqg)
964                         - cfqg->service_tree_idle.count;
965 
966         BUG_ON(nr_sync < 0);
967         used_sl = charge = cfq_cfqq_slice_usage(cfqq, &unaccounted_sl);
968 
969         if (iops_mode(cfqd))
970                 charge = cfqq->slice_dispatch;
971         else if (!cfq_cfqq_sync(cfqq) && !nr_sync)
972                 charge = cfqq->allocated_slice;
973 
974         /* Can't update vdisktime while group is on service tree */
975         cfq_group_service_tree_del(st, cfqg);
976         cfqg->vdisktime += cfq_scale_slice(charge, cfqg);
977         /* If a new weight was requested, update now, off tree */
978         cfq_group_service_tree_add(st, cfqg);
979 
980         /* This group is being expired. Save the context */
981         if (time_after(cfqd->workload_expires, jiffies)) {
982                 cfqg->saved_workload_slice = cfqd->workload_expires
983                                                 - jiffies;
984                 cfqg->saved_workload = cfqd->serving_type;
985                 cfqg->saved_serving_prio = cfqd->serving_prio;
986         } else
987                 cfqg->saved_workload_slice = 0;
988 
989         cfq_log_cfqg(cfqd, cfqg, "served: vt=%llu min_vt=%llu", cfqg->vdisktime,
990                                         st->min_vdisktime);
991         cfq_log_cfqq(cfqq->cfqd, cfqq,
992                      "sl_used=%u disp=%u charge=%u iops=%u sect=%lu",
993                      used_sl, cfqq->slice_dispatch, charge,
994                      iops_mode(cfqd), cfqq->nr_sectors);
995         cfq_blkiocg_update_timeslice_used(&cfqg->blkg, used_sl,
996                                           unaccounted_sl);
997         cfq_blkiocg_set_start_empty_time(&cfqg->blkg);
998 }
999 
1000 #ifdef CONFIG_CFQ_GROUP_IOSCHED
1001 static inline struct cfq_group *cfqg_of_blkg(struct blkio_group *blkg)
1002 {
1003         if (blkg)
1004                 return container_of(blkg, struct cfq_group, blkg);
1005         return NULL;
1006 }
1007 
1008 void cfq_update_blkio_group_weight(void *key, struct blkio_group *blkg,
1009                                         unsigned int weight)
1010 {
1011         struct cfq_group *cfqg = cfqg_of_blkg(blkg);
1012         cfqg->new_weight = weight;
1013         cfqg->needs_update = true;
1014 }
1015 
1016 static void cfq_init_add_cfqg_lists(struct cfq_data *cfqd,
1017                         struct cfq_group *cfqg, struct blkio_cgroup *blkcg)
1018 {
1019         struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
1020         unsigned int major, minor;
1021 
1022         /*
1023          * Add group onto cgroup list. It might happen that bdi->dev is
1024          * not initialized yet. Initialize this new group without major
1025          * and minor info and this info will be filled in once a new thread
1026          * comes for IO.
1027          */
1028         if (bdi->dev) {
1029                 sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
1030                 cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg,
1031                                         (void *)cfqd, MKDEV(major, minor));
1032         } else
1033                 cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg,
1034                                         (void *)cfqd, 0);
1035 
1036         cfqd->nr_blkcg_linked_grps++;
1037         cfqg->weight = blkcg_get_weight(blkcg, cfqg->blkg.dev);
1038 
1039         /* Add group on cfqd list */
1040         hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
1041 }
1042 
1043 /*
1044  * Should be called from sleepable context. No request queue lock as per
1045  * cpu stats are allocated dynamically and alloc_percpu needs to be called
1046  * from sleepable context.
1047  */
1048 static struct cfq_group * cfq_alloc_cfqg(struct cfq_data *cfqd)
1049 {
1050         struct cfq_group *cfqg = NULL;
1051         int i, j, ret;
1052         struct cfq_rb_root *st;
1053 
1054         cfqg = kzalloc_node(sizeof(*cfqg), GFP_ATOMIC, cfqd->queue->node);
1055         if (!cfqg)
1056                 return NULL;
1057 
1058         for_each_cfqg_st(cfqg, i, j, st)
1059                 *st = CFQ_RB_ROOT;
1060         RB_CLEAR_NODE(&cfqg->rb_node);
1061 
1062         /*
1063          * Take the initial reference that will be released on destroy
1064          * This can be thought of a joint reference by cgroup and
1065          * elevator which will be dropped by either elevator exit
1066          * or cgroup deletion path depending on who is exiting first.
1067          */
1068         cfqg->ref = 1;
1069 
1070         ret = blkio_alloc_blkg_stats(&cfqg->blkg);
1071         if (ret) {
1072                 kfree(cfqg);
1073                 return NULL;
1074         }
1075 
1076         return cfqg;
1077 }
1078 
1079 static struct cfq_group *
1080 cfq_find_cfqg(struct cfq_data *cfqd, struct blkio_cgroup *blkcg)
1081 {
1082         struct cfq_group *cfqg = NULL;
1083         void *key = cfqd;
1084         struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
1085         unsigned int major, minor;
1086 
1087         /*
1088          * This is the common case when there are no blkio cgroups.
1089          * Avoid lookup in this case
1090          */
1091         if (blkcg == &blkio_root_cgroup)
1092                 cfqg = &cfqd->root_group;
1093         else
1094                 cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));
1095 
1096         if (cfqg && !cfqg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
1097                 sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
1098                 cfqg->blkg.dev = MKDEV(major, minor);
1099         }
1100 
1101         return cfqg;
1102 }
1103 
1104 /*
1105  * Search for the cfq group current task belongs to. request_queue lock must
1106  * be held.
1107  */
1108 static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd)
1109 {
1110         struct blkio_cgroup *blkcg;
1111         struct cfq_group *cfqg = NULL, *__cfqg = NULL;
1112         struct request_queue *q = cfqd->queue;
1113 
1114         rcu_read_lock();
1115         blkcg = task_blkio_cgroup(current);
1116         cfqg = cfq_find_cfqg(cfqd, blkcg);
1117         if (cfqg) {
1118                 rcu_read_unlock();
1119                 return cfqg;
1120         }
1121 
1122         /*
1123          * Need to allocate a group. Allocation of group also needs allocation
1124          * of per cpu stats which in-turn takes a mutex() and can block. Hence
1125          * we need to drop rcu lock and queue_lock before we call alloc.
1126          *
1127          * Not taking any queue reference here and assuming that queue is
1128          * around by the time we return. CFQ queue allocation code does
1129          * the same. It might be racy though.
1130          */
1131 
1132         rcu_read_unlock();
1133         spin_unlock_irq(q->queue_lock);
1134 
1135         cfqg = cfq_alloc_cfqg(cfqd);
1136 
1137         spin_lock_irq(q->queue_lock);
1138 
1139         rcu_read_lock();
1140         blkcg = task_blkio_cgroup(current);
1141 
1142         /*
1143          * If some other thread already allocated the group while we were
1144          * not holding queue lock, free up the group
1145          */
1146         __cfqg = cfq_find_cfqg(cfqd, blkcg);
1147 
1148         if (__cfqg) {
1149                 kfree(cfqg);
1150                 rcu_read_unlock();
1151                 return __cfqg;
1152         }
1153 
1154         if (!cfqg)
1155                 cfqg = &cfqd->root_group;
1156 
1157         cfq_init_add_cfqg_lists(cfqd, cfqg, blkcg);
1158         rcu_read_unlock();
1159         return cfqg;
1160 }
1161 
1162 static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
1163 {
1164         cfqg->ref++;
1165         return cfqg;
1166 }
1167 
1168 static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
1169 {
1170         /* Currently, all async queues are mapped to root group */
1171         if (!cfq_cfqq_sync(cfqq))
1172                 cfqg = &cfqq->cfqd->root_group;
1173 
1174         cfqq->cfqg = cfqg;
1175         /* cfqq reference on cfqg */
1176         cfqq->cfqg->ref++;
1177 }
1178 
1179 static void cfq_put_cfqg(struct cfq_group *cfqg)
1180 {
1181         struct cfq_rb_root *st;
1182         int i, j;
1183 
1184         BUG_ON(cfqg->ref <= 0);
1185         cfqg->ref--;
1186         if (cfqg->ref)
1187                 return;
1188         for_each_cfqg_st(cfqg, i, j, st)
1189                 BUG_ON(!RB_EMPTY_ROOT(&st->rb));
1190         free_percpu(cfqg->blkg.stats_cpu);
1191         kfree(cfqg);
1192 }
1193 
1194 static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg)
1195 {
1196         /* Something wrong if we are trying to remove same group twice */
1197         BUG_ON(hlist_unhashed(&cfqg->cfqd_node));
1198 
1199         hlist_del_init(&cfqg->cfqd_node);
1200 
1201         /*
1202          * Put the reference taken at the time of creation so that when all
1203          * queues are gone, group can be destroyed.
1204          */
1205         cfq_put_cfqg(cfqg);
1206 }
1207 
1208 static void cfq_release_cfq_groups(struct cfq_data *cfqd)
1209 {
1210         struct hlist_node *pos, *n;
1211         struct cfq_group *cfqg;
1212 
1213         hlist_for_each_entry_safe(cfqg, pos, n, &cfqd->cfqg_list, cfqd_node) {
1214                 /*
1215                  * If cgroup removal path got to blk_group first and removed
1216                  * it from cgroup list, then it will take care of destroying
1217                  * cfqg also.
1218                  */
1219                 if (!cfq_blkiocg_del_blkio_group(&cfqg->blkg))
1220                         cfq_destroy_cfqg(cfqd, cfqg);
1221         }
1222 }
1223 
1224 /*
1225  * Blk cgroup controller notification saying that blkio_group object is being
1226  * delinked as associated cgroup object is going away. That also means that
1227  * no new IO will come in this group. So get rid of this group as soon as
1228  * any pending IO in the group is finished.
1229  *
1230  * This function is called under rcu_read_lock(). key is the rcu protected
1231  * pointer. That means "key" is a valid cfq_data pointer as long as we are rcu
1232  * read lock.
1233  *
1234  * "key" was fetched from blkio_group under blkio_cgroup->lock. That means
1235  * it should not be NULL as even if elevator was exiting, cgroup deltion
1236  * path got to it first.
1237  */
1238 void cfq_unlink_blkio_group(void *key, struct blkio_group *blkg)
1239 {
1240         unsigned long  flags;
1241         struct cfq_data *cfqd = key;
1242 
1243         spin_lock_irqsave(cfqd->queue->queue_lock, flags);
1244         cfq_destroy_cfqg(cfqd, cfqg_of_blkg(blkg));
1245         spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
1246 }
1247 
1248 #else /* GROUP_IOSCHED */
1249 static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd)
1250 {
1251         return &cfqd->root_group;
1252 }
1253 
1254 static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
1255 {
1256         return cfqg;
1257 }
1258 
1259 static inline void
1260 cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) {
1261         cfqq->cfqg = cfqg;
1262 }
1263 
1264 static void cfq_release_cfq_groups(struct cfq_data *cfqd) {}
1265 static inline void cfq_put_cfqg(struct cfq_group *cfqg) {}
1266 
1267 #endif /* GROUP_IOSCHED */
1268 
1269 /*
1270  * The cfqd->service_trees holds all pending cfq_queue's that have
1271  * requests waiting to be processed. It is sorted in the order that
1272  * we will service the queues.
1273  */
1274 static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
1275                                  bool add_front)
1276 {
1277         struct rb_node **p, *parent;
1278         struct cfq_queue *__cfqq;
1279         unsigned long rb_key;
1280         struct cfq_rb_root *service_tree;
1281         int left;
1282         int new_cfqq = 1;
1283 
1284         service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),
1285                                                 cfqq_type(cfqq));
1286         if (cfq_class_idle(cfqq)) {
1287                 rb_key = CFQ_IDLE_DELAY;
1288                 parent = rb_last(&service_tree->rb);
1289                 if (parent && parent != &cfqq->rb_node) {
1290                         __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
1291                         rb_key += __cfqq->rb_key;
1292                 } else
1293                         rb_key += jiffies;
1294         } else if (!add_front) {
1295                 /*
1296                  * Get our rb key offset. Subtract any residual slice
1297                  * value carried from last service. A negative resid
1298                  * count indicates slice overrun, and this should position
1299                  * the next service time further away in the tree.
1300                  */
1301                 rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
1302                 rb_key -= cfqq->slice_resid;
1303                 cfqq->slice_resid = 0;
1304         } else {
1305                 rb_key = -HZ;
1306                 __cfqq = cfq_rb_first(service_tree);
1307                 rb_key += __cfqq ? __cfqq->rb_key : jiffies;
1308         }
1309 
1310         if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
1311                 new_cfqq = 0;
1312                 /*
1313                  * same position, nothing more to do
1314                  */
1315                 if (rb_key == cfqq->rb_key &&
1316                     cfqq->service_tree == service_tree)
1317                         return;
1318 
1319                 cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
1320                 cfqq->service_tree = NULL;
1321         }
1322 
1323         left = 1;
1324         parent = NULL;
1325         cfqq->service_tree = service_tree;
1326         p = &service_tree->rb.rb_node;
1327         while (*p) {
1328                 struct rb_node **n;
1329 
1330                 parent = *p;
1331                 __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
1332 
1333                 /*
1334                  * sort by key, that represents service time.
1335                  */
1336                 if (time_before(rb_key, __cfqq->rb_key))
1337                         n = &(*p)->rb_left;
1338                 else {
1339                         n = &(*p)->rb_right;
1340                         left = 0;
1341                 }
1342 
1343                 p = n;
1344         }
1345 
1346         if (left)
1347                 service_tree->left = &cfqq->rb_node;
1348 
1349         cfqq->rb_key = rb_key;
1350         rb_link_node(&cfqq->rb_node, parent, p);
1351         rb_insert_color(&cfqq->rb_node, &service_tree->rb);
1352         service_tree->count++;
1353         if (add_front || !new_cfqq)
1354                 return;
1355         cfq_group_notify_queue_add(cfqd, cfqq->cfqg);
1356 }
1357 
1358 static struct cfq_queue *
1359 cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
1360                      sector_t sector, struct rb_node **ret_parent,
1361                      struct rb_node ***rb_link)
1362 {
1363         struct rb_node **p, *parent;
1364         struct cfq_queue *cfqq = NULL;
1365 
1366         parent = NULL;
1367         p = &root->rb_node;
1368         while (*p) {
1369                 struct rb_node **n;
1370 
1371                 parent = *p;
1372                 cfqq = rb_entry(parent, struct cfq_queue, p_node);
1373 
1374                 /*
1375                  * Sort strictly based on sector.  Smallest to the left,
1376                  * largest to the right.
1377                  */
1378                 if (sector > blk_rq_pos(cfqq->next_rq))
1379                         n = &(*p)->rb_right;
1380                 else if (sector < blk_rq_pos(cfqq->next_rq))
1381                         n = &(*p)->rb_left;
1382                 else
1383                         break;
1384                 p = n;
1385                 cfqq = NULL;
1386         }
1387 
1388         *ret_parent = parent;
1389         if (rb_link)
1390                 *rb_link = p;
1391         return cfqq;
1392 }
1393 
1394 static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1395 {
1396         struct rb_node **p, *parent;
1397         struct cfq_queue *__cfqq;
1398 
1399         if (cfqq->p_root) {
1400                 rb_erase(&cfqq->p_node, cfqq->p_root);
1401                 cfqq->p_root = NULL;
1402         }
1403 
1404         if (cfq_class_idle(cfqq))
1405                 return;
1406         if (!cfqq->next_rq)
1407                 return;
1408 
1409         cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];
1410         __cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
1411                                       blk_rq_pos(cfqq->next_rq), &parent, &p);
1412         if (!__cfqq) {
1413                 rb_link_node(&cfqq->p_node, parent, p);
1414                 rb_insert_color(&cfqq->p_node, cfqq->p_root);
1415         } else
1416                 cfqq->p_root = NULL;
1417 }
1418 
1419 /*
1420  * Update cfqq's position in the service tree.
1421  */
1422 static void cfq_resort_rr_list(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1423 {
1424         /*
1425          * Resorting requires the cfqq to be on the RR list already.
1426          */
1427         if (cfq_cfqq_on_rr(cfqq)) {
1428                 cfq_service_tree_add(cfqd, cfqq, 0);
1429                 cfq_prio_tree_add(cfqd, cfqq);
1430         }
1431 }
1432 
1433 /*
1434  * add to busy list of queues for service, trying to be fair in ordering
1435  * the pending list according to last request service
1436  */
1437 static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1438 {
1439         cfq_log_cfqq(cfqd, cfqq, "add_to_rr");
1440         BUG_ON(cfq_cfqq_on_rr(cfqq));
1441         cfq_mark_cfqq_on_rr(cfqq);
1442         cfqd->busy_queues++;
1443         if (cfq_cfqq_sync(cfqq))
1444                 cfqd->busy_sync_queues++;
1445 
1446         cfq_resort_rr_list(cfqd, cfqq);
1447 }
1448 
1449 /*
1450  * Called when the cfqq no longer has requests pending, remove it from
1451  * the service tree.
1452  */
1453 static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1454 {
1455         cfq_log_cfqq(cfqd, cfqq, "del_from_rr");
1456         BUG_ON(!cfq_cfqq_on_rr(cfqq));
1457         cfq_clear_cfqq_on_rr(cfqq);
1458 
1459         if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
1460                 cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
1461                 cfqq->service_tree = NULL;
1462         }
1463         if (cfqq->p_root) {
1464                 rb_erase(&cfqq->p_node, cfqq->p_root);
1465                 cfqq->p_root = NULL;
1466         }
1467 
1468         cfq_group_notify_queue_del(cfqd, cfqq->cfqg);
1469         BUG_ON(!cfqd->busy_queues);
1470         cfqd->busy_queues--;
1471         if (cfq_cfqq_sync(cfqq))
1472                 cfqd->busy_sync_queues--;
1473 }
1474 
1475 /*
1476  * rb tree support functions
1477  */
1478 static void cfq_del_rq_rb(struct request *rq)
1479 {
1480         struct cfq_queue *cfqq = RQ_CFQQ(rq);
1481         const int sync = rq_is_sync(rq);
1482 
1483         BUG_ON(!cfqq->queued[sync]);
1484         cfqq->queued[sync]--;
1485 
1486         elv_rb_del(&cfqq->sort_list, rq);
1487 
1488         if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list)) {
1489                 /*
1490                  * Queue will be deleted from service tree when we actually
1491                  * expire it later. Right now just remove it from prio tree
1492                  * as it is empty.
1493                  */
1494                 if (cfqq->p_root) {
1495                         rb_erase(&cfqq->p_node, cfqq->p_root);
1496                         cfqq->p_root = NULL;
1497                 }
1498         }
1499 }
1500 
1501 static void cfq_add_rq_rb(struct request *rq)
1502 {
1503         struct cfq_queue *cfqq = RQ_CFQQ(rq);
1504         struct cfq_data *cfqd = cfqq->cfqd;
1505         struct request *__alias, *prev;
1506 
1507         cfqq->queued[rq_is_sync(rq)]++;
1508 
1509         /*
1510          * looks a little odd, but the first insert might return an alias.
1511          * if that happens, put the alias on the dispatch list
1512          */
1513         while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL)
1514                 cfq_dispatch_insert(cfqd->queue, __alias);
1515 
1516         if (!cfq_cfqq_on_rr(cfqq))
1517                 cfq_add_cfqq_rr(cfqd, cfqq);
1518 
1519         /*
1520          * check if this request is a better next-serve candidate
1521          */
1522         prev = cfqq->next_rq;
1523         cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq, cfqd->last_position);
1524 
1525         /*
1526          * adjust priority tree position, if ->next_rq changes
1527          */
1528         if (prev != cfqq->next_rq)
1529                 cfq_prio_tree_add(cfqd, cfqq);
1530 
1531         BUG_ON(!cfqq->next_rq);
1532 }
1533 
1534 static void cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)
1535 {
1536         elv_rb_del(&cfqq->sort_list, rq);
1537         cfqq->queued[rq_is_sync(rq)]--;
1538         cfq_blkiocg_update_io_remove_stats(&(RQ_CFQG(rq))->blkg,
1539                                         rq_data_dir(rq), rq_is_sync(rq));
1540         cfq_add_rq_rb(rq);
1541         cfq_blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,
1542                         &cfqq->cfqd->serving_group->blkg, rq_data_dir(rq),
1543                         rq_is_sync(rq));
1544 }
1545 
1546 static struct request *
1547 cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
1548 {
1549         struct task_struct *tsk = current;
1550         struct cfq_io_context *cic;
1551         struct cfq_queue *cfqq;
1552 
1553         cic = cfq_cic_lookup(cfqd, tsk->io_context);
1554         if (!cic)
1555                 return NULL;
1556 
1557         cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
1558         if (cfqq) {
1559                 sector_t sector = bio->bi_sector + bio_sectors(bio);
1560 
1561                 return elv_rb_find(&cfqq->sort_list, sector);
1562         }
1563 
1564         return NULL;
1565 }
1566 
1567 static void cfq_activate_request(struct request_queue *q, struct request *rq)
1568 {
1569         struct cfq_data *cfqd = q->elevator->elevator_data;
1570 
1571         cfqd->rq_in_driver++;
1572         cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
1573                                                 cfqd->rq_in_driver);
1574 
1575         cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
1576 }
1577 
1578 static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
1579 {
1580         struct cfq_data *cfqd = q->elevator->elevator_data;
1581 
1582         WARN_ON(!cfqd->rq_in_driver);
1583         cfqd->rq_in_driver--;
1584         cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
1585                                                 cfqd->rq_in_driver);
1586 }
1587 
1588 static void cfq_remove_request(struct request *rq)
1589 {
1590         struct cfq_queue *cfqq = RQ_CFQQ(rq);
1591 
1592         if (cfqq->next_rq == rq)
1593                 cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);
1594 
1595         list_del_init(&rq->queuelist);
1596         cfq_del_rq_rb(rq);
1597 
1598         cfqq->cfqd->rq_queued--;
1599         cfq_blkiocg_update_io_remove_stats(&(RQ_CFQG(rq))->blkg,
1600                                         rq_data_dir(rq), rq_is_sync(rq));
1601         if (rq->cmd_flags & REQ_META) {
1602                 WARN_ON(!cfqq->meta_pending);
1603                 cfqq->meta_pending--;
1604         }
1605 }
1606 
1607 static int cfq_merge(struct request_queue *q, struct request **req,
1608                      struct bio *bio)
1609 {
1610         struct cfq_data *cfqd = q->elevator->elevator_data;
1611         struct request *__rq;
1612 
1613         __rq = cfq_find_rq_fmerge(cfqd, bio);
1614         if (__rq && elv_rq_merge_ok(__rq, bio)) {
1615                 *req = __rq;
1616                 return ELEVATOR_FRONT_MERGE;
1617         }
1618 
1619         return ELEVATOR_NO_MERGE;
1620 }
1621 
1622 static void cfq_merged_request(struct request_queue *q, struct request *req,
1623                                int type)
1624 {
1625         if (type == ELEVATOR_FRONT_MERGE) {
1626                 struct cfq_queue *cfqq = RQ_CFQQ(req);
1627 
1628                 cfq_reposition_rq_rb(cfqq, req);
1629         }
1630 }
1631 
1632 static void cfq_bio_merged(struct request_queue *q, struct request *req,
1633                                 struct bio *bio)
1634 {
1635         cfq_blkiocg_update_io_merged_stats(&(RQ_CFQG(req))->blkg,
1636                                         bio_data_dir(bio), cfq_bio_sync(bio));
1637 }
1638 
1639 static void
1640 cfq_merged_requests(struct request_queue *q, struct request *rq,
1641                     struct request *next)
1642 {
1643         struct cfq_queue *cfqq = RQ_CFQQ(rq);
1644         /*
1645          * reposition in fifo if next is older than rq
1646          */
1647         if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
1648             time_before(rq_fifo_time(next), rq_fifo_time(rq))) {
1649                 list_move(&rq->queuelist, &next->queuelist);
1650                 rq_set_fifo_time(rq, rq_fifo_time(next));
1651         }
1652 
1653         if (cfqq->next_rq == next)
1654                 cfqq->next_rq = rq;
1655         cfq_remove_request(next);
1656         cfq_blkiocg_update_io_merged_stats(&(RQ_CFQG(rq))->blkg,
1657                                         rq_data_dir(next), rq_is_sync(next));
1658 }
1659 
1660 static int cfq_allow_merge(struct request_queue *q, struct request *rq,
1661                            struct bio *bio)
1662 {
1663         struct cfq_data *cfqd = q->elevator->elevator_data;
1664         struct cfq_io_context *cic;
1665         struct cfq_queue *cfqq;
1666 
1667         /*
1668          * Disallow merge of a sync bio into an async request.
1669          */
1670         if (cfq_bio_sync(bio) && !rq_is_sync(rq))
1671                 return false;
1672 
1673         /*
1674          * Lookup the cfqq that this bio will be queued with. Allow
1675          * merge only if rq is queued there.
1676          */
1677         cic = cfq_cic_lookup(cfqd, current->io_context);
1678         if (!cic)
1679                 return false;
1680 
1681         cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
1682         return cfqq == RQ_CFQQ(rq);
1683 }
1684 
1685 static inline void cfq_del_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1686 {
1687         del_timer(&cfqd->idle_slice_timer);
1688         cfq_blkiocg_update_idle_time_stats(&cfqq->cfqg->blkg);
1689 }
1690 
1691 static void __cfq_set_active_queue(struct cfq_data *cfqd,
1692                                    struct cfq_queue *cfqq)
1693 {
1694         if (cfqq) {
1695                 cfq_log_cfqq(cfqd, cfqq, "set_active wl_prio:%d wl_type:%d",
1696                                 cfqd->serving_prio, cfqd->serving_type);
1697                 cfq_blkiocg_update_avg_queue_size_stats(&cfqq->cfqg->blkg);
1698                 cfqq->slice_start = 0;
1699                 cfqq->dispatch_start = jiffies;
1700                 cfqq->allocated_slice = 0;
1701                 cfqq->slice_end = 0;
1702                 cfqq->slice_dispatch = 0;
1703                 cfqq->nr_sectors = 0;
1704 
1705                 cfq_clear_cfqq_wait_request(cfqq);
1706                 cfq_clear_cfqq_must_dispatch(cfqq);
1707                 cfq_clear_cfqq_must_alloc_slice(cfqq);
1708                 cfq_clear_cfqq_fifo_expire(cfqq);
1709                 cfq_mark_cfqq_slice_new(cfqq);
1710 
1711                 cfq_del_timer(cfqd, cfqq);
1712         }
1713 
1714         cfqd->active_queue = cfqq;
1715 }
1716 
1717 /*
1718  * current cfqq expired its slice (or was too idle), select new one
1719  */
1720 static void
1721 __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
1722                     bool timed_out)
1723 {
1724         cfq_log_cfqq(cfqd, cfqq, "slice expired t=%d", timed_out);
1725 
1726         if (cfq_cfqq_wait_request(cfqq))
1727                 cfq_del_timer(cfqd, cfqq);
1728 
1729         cfq_clear_cfqq_wait_request(cfqq);
1730         cfq_clear_cfqq_wait_busy(cfqq);
1731 
1732         /*
1733          * If this cfqq is shared between multiple processes, check to
1734          * make sure that those processes are still issuing I/Os within
1735          * the mean seek distance.  If not, it may be time to break the
1736          * queues apart again.
1737          */
1738         if (cfq_cfqq_coop(cfqq) && CFQQ_SEEKY(cfqq))
1739                 cfq_mark_cfqq_split_coop(cfqq);
1740 
1741         /*
1742          * store what was left of this slice, if the queue idled/timed out
1743          */
1744         if (timed_out) {
1745                 if (cfq_cfqq_slice_new(cfqq))
1746                         cfqq->slice_resid = cfq_scaled_cfqq_slice(cfqd, cfqq);
1747                 else
1748                         cfqq->slice_resid = cfqq->slice_end - jiffies;
1749                 cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
1750         }
1751 
1752         cfq_group_served(cfqd, cfqq->cfqg, cfqq);
1753 
1754         if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
1755                 cfq_del_cfqq_rr(cfqd, cfqq);
1756 
1757         cfq_resort_rr_list(cfqd, cfqq);
1758 
1759         if (cfqq == cfqd->active_queue)
1760                 cfqd->active_queue = NULL;
1761 
1762         if (cfqd->active_cic) {
1763                 put_io_context(cfqd->active_cic->ioc);
1764                 cfqd->active_cic = NULL;
1765         }
1766 }
1767 
1768 static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out)
1769 {
1770         struct cfq_queue *cfqq = cfqd->active_queue;
1771 
1772         if (cfqq)
1773                 __cfq_slice_expired(cfqd, cfqq, timed_out);
1774 }
1775 
1776 /*
1777  * Get next queue for service. Unless we have a queue preemption,
1778  * we'll simply select the first cfqq in the service tree.
1779  */
1780 static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
1781 {
1782         struct cfq_rb_root *service_tree =
1783                 service_tree_for(cfqd->serving_group, cfqd->serving_prio,
1784                                         cfqd->serving_type);
1785 
1786         if (!cfqd->rq_queued)
1787                 return NULL;
1788 
1789         /* There is nothing to dispatch */
1790         if (!service_tree)
1791                 return NULL;
1792         if (RB_EMPTY_ROOT(&service_tree->rb))
1793                 return NULL;
1794         return cfq_rb_first(service_tree);
1795 }
1796 
1797 static struct cfq_queue *cfq_get_next_queue_forced(struct cfq_data *cfqd)
1798 {
1799         struct cfq_group *cfqg;
1800         struct cfq_queue *cfqq;
1801         int i, j;
1802         struct cfq_rb_root *st;
1803 
1804         if (!cfqd->rq_queued)
1805                 return NULL;
1806 
1807         cfqg = cfq_get_next_cfqg(cfqd);
1808         if (!cfqg)
1809                 return NULL;
1810 
1811         for_each_cfqg_st(cfqg, i, j, st)
1812                 if ((cfqq = cfq_rb_first(st)) != NULL)
1813                         return cfqq;
1814         return NULL;
1815 }
1816 
1817 /*
1818  * Get and set a new active queue for service.
1819  */
1820 static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd,
1821                                               struct cfq_queue *cfqq)
1822 {
1823         if (!cfqq)
1824                 cfqq = cfq_get_next_queue(cfqd);
1825 
1826         __cfq_set_active_queue(cfqd, cfqq);
1827         return cfqq;
1828 }
1829 
1830 static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
1831                                           struct request *rq)
1832 {
1833         if (blk_rq_pos(rq) >= cfqd->last_position)
1834                 return blk_rq_pos(rq) - cfqd->last_position;
1835         else
1836                 return cfqd->last_position - blk_rq_pos(rq);
1837 }
1838 
1839 static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq,
1840                                struct request *rq)
1841 {
1842         return cfq_dist_from_last(cfqd, rq) <= CFQQ_CLOSE_THR;
1843 }
1844 
1845 static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
1846                                     struct cfq_queue *cur_cfqq)
1847 {
1848         struct rb_root *root = &cfqd->prio_trees[cur_cfqq->org_ioprio];
1849         struct rb_node *parent, *node;
1850         struct cfq_queue *__cfqq;
1851         sector_t sector = cfqd->last_position;
1852 
1853         if (RB_EMPTY_ROOT(root))
1854                 return NULL;
1855 
1856         /*
1857          * First, if we find a request starting at the end of the last
1858          * request, choose it.
1859          */
1860         __cfqq = cfq_prio_tree_lookup(cfqd, root, sector, &parent, NULL);
1861         if (__cfqq)
1862                 return __cfqq;
1863 
1864         /*
1865          * If the exact sector wasn't found, the parent of the NULL leaf
1866          * will contain the closest sector.
1867          */
1868         __cfqq = rb_entry(parent, struct cfq_queue, p_node);
1869         if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
1870                 return __cfqq;
1871 
1872         if (blk_rq_pos(__cfqq->next_rq) < sector)
1873                 node = rb_next(&__cfqq->p_node);
1874         else
1875                 node = rb_prev(&__cfqq->p_node);
1876         if (!node)
1877                 return NULL;
1878 
1879         __cfqq = rb_entry(node, struct cfq_queue, p_node);
1880         if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
1881                 return __cfqq;
1882 
1883         return NULL;
1884 }
1885 
1886 /*
1887  * cfqd - obvious
1888  * cur_cfqq - passed in so that we don't decide that the current queue is
1889  *            closely cooperating with itself.
1890  *
1891  * So, basically we're assuming that that cur_cfqq has dispatched at least
1892  * one request, and that cfqd->last_position reflects a position on the disk
1893  * associated with the I/O issued by cur_cfqq.  I'm not sure this is a valid
1894  * assumption.
1895  */
1896 static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
1897                                               struct cfq_queue *cur_cfqq)
1898 {
1899         struct cfq_queue *cfqq;
1900 
1901         if (cfq_class_idle(cur_cfqq))
1902                 return NULL;
1903         if (!cfq_cfqq_sync(cur_cfqq))
1904                 return NULL;
1905         if (CFQQ_SEEKY(cur_cfqq))
1906                 return NULL;
1907 
1908         /*
1909          * Don't search priority tree if it's the only queue in the group.
1910          */
1911         if (cur_cfqq->cfqg->nr_cfqq == 1)
1912                 return NULL;
1913 
1914         /*
1915          * We should notice if some of the queues are cooperating, eg
1916          * working closely on the same area of the disk. In that case,
1917          * we can group them together and don't waste time idling.
1918          */
1919         cfqq = cfqq_close(cfqd, cur_cfqq);
1920         if (!cfqq)
1921                 return NULL;
1922 
1923         /* If new queue belongs to different cfq_group, don't choose it */
1924         if (cur_cfqq->cfqg != cfqq->cfqg)
1925                 return NULL;
1926 
1927         /*
1928          * It only makes sense to merge sync queues.
1929          */
1930         if (!cfq_cfqq_sync(cfqq))
1931                 return NULL;
1932         if (CFQQ_SEEKY(cfqq))
1933                 return NULL;
1934 
1935         /*
1936          * Do not merge queues of different priority classes
1937          */
1938         if (cfq_class_rt(cfqq) != cfq_class_rt(cur_cfqq))
1939                 return NULL;
1940 
1941         return cfqq;
1942 }
1943 
1944 /*
1945  * Determine whether we should enforce idle window for this queue.
1946  */
1947 
1948 static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1949 {
1950         enum wl_prio_t prio = cfqq_prio(cfqq);
1951         struct cfq_rb_root *service_tree = cfqq->service_tree;
1952 
1953         BUG_ON(!service_tree);
1954         BUG_ON(!service_tree->count);
1955 
1956         if (!cfqd->cfq_slice_idle)
1957                 return false;
1958 
1959         /* We never do for idle class queues. */
1960         if (prio == IDLE_WORKLOAD)
1961                 return false;
1962 
1963         /* We do for queues that were marked with idle window flag. */
1964         if (cfq_cfqq_idle_window(cfqq) &&
1965            !(blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag))
1966                 return true;
1967 
1968         /*
1969          * Otherwise, we do only if they are the last ones
1970          * in their service tree.
1971          */
1972         if (service_tree->count == 1 && cfq_cfqq_sync(cfqq))
1973                 return true;
1974         cfq_log_cfqq(cfqd, cfqq, "Not idling. st->count:%d",
1975                         service_tree->count);
1976         return false;
1977 }
1978 
1979 static void cfq_arm_slice_timer(struct cfq_data *cfqd)
1980 {
1981         struct cfq_queue *cfqq = cfqd->active_queue;
1982         struct cfq_io_context *cic;
1983         unsigned long sl, group_idle = 0;
1984 
1985         /*
1986          * SSD device without seek penalty, disable idling. But only do so
1987          * for devices that support queuing, otherwise we still have a problem
1988          * with sync vs async workloads.
1989          */
1990         if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag)
1991                 return;
1992 
1993         WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
1994         WARN_ON(cfq_cfqq_slice_new(cfqq));
1995 
1996         /*
1997          * idle is disabled, either manually or by past process history
1998          */
1999         if (!cfq_should_idle(cfqd, cfqq)) {
2000                 /* no queue idling. Check for group idling */
2001                 if (cfqd->cfq_group_idle)
2002                         group_idle = cfqd->cfq_group_idle;
2003                 else
2004                         return;
2005         }
2006 
2007         /*
2008          * still active requests from this queue, don't idle
2009          */
2010         if (cfqq->dispatched)
2011                 return;
2012 
2013         /*
2014          * task has exited, don't wait
2015          */
2016         cic = cfqd->active_cic;
2017         if (!cic || !atomic_read(&cic->ioc->nr_tasks))
2018                 return;
2019 
2020         /*
2021          * If our average think time is larger than the remaining time
2022          * slice, then don't idle. This avoids overrunning the allotted
2023          * time slice.
2024          */
2025         if (sample_valid(cic->ttime_samples) &&
2026             (cfqq->slice_end - jiffies < cic->ttime_mean)) {
2027                 cfq_log_cfqq(cfqd, cfqq, "Not idling. think_time:%lu",
2028                              cic->ttime_mean);
2029                 return;
2030         }
2031 
2032         /* There are other queues in the group, don't do group idle */
2033         if (group_idle && cfqq->cfqg->nr_cfqq > 1)
2034                 return;
2035 
2036         cfq_mark_cfqq_wait_request(cfqq);
2037 
2038         if (group_idle)
2039                 sl = cfqd->cfq_group_idle;
2040         else
2041                 sl = cfqd->cfq_slice_idle;
2042 
2043         mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
2044         cfq_blkiocg_update_set_idle_time_stats(&cfqq->cfqg->blkg);
2045         cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu group_idle: %d", sl,
2046                         group_idle ? 1 : 0);
2047 }
2048 
2049 /*
2050  * Move request from internal lists to the request queue dispatch list.
2051  */
2052 static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
2053 {
2054         struct cfq_data *cfqd = q->elevator->elevator_data;
2055         struct cfq_queue *cfqq = RQ_CFQQ(rq);
2056 
2057         cfq_log_cfqq(cfqd, cfqq, "dispatch_insert");
2058 
2059         cfqq->next_rq = cfq_find_next_rq(cfqd, cfqq, rq);
2060         cfq_remove_request(rq);
2061         cfqq->dispatched++;
2062         (RQ_CFQG(rq))->dispatched++;
2063         elv_dispatch_sort(q, rq);
2064 
2065         cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]++;
2066         cfqq->nr_sectors += blk_rq_sectors(rq);
2067         cfq_blkiocg_update_dispatch_stats(&cfqq->cfqg->blkg, blk_rq_bytes(rq),
2068                                         rq_data_dir(rq), rq_is_sync(rq));
2069 }
2070 
2071 /*
2072  * return expired entry, or NULL to just start from scratch in rbtree
2073  */
2074 static struct request *cfq_check_fifo(struct cfq_queue *cfqq)
2075 {
2076         struct request *rq = NULL;
2077 
2078         if (cfq_cfqq_fifo_expire(cfqq))
2079                 return NULL;
2080 
2081         cfq_mark_cfqq_fifo_expire(cfqq);
2082 
2083         if (list_empty(&cfqq->fifo))
2084                 return NULL;
2085 
2086         rq = rq_entry_fifo(cfqq->fifo.next);
2087         if (time_before(jiffies, rq_fifo_time(rq)))
2088                 rq = NULL;
2089 
2090         cfq_log_cfqq(cfqq->cfqd, cfqq, "fifo=%p", rq);
2091         return rq;
2092 }
2093 
2094 static inline int
2095 cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
2096 {
2097         const int base_rq = cfqd->cfq_slice_async_rq;
2098 
2099         WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);
2100 
2101         return 2 * base_rq * (IOPRIO_BE_NR - cfqq->ioprio);
2102 }
2103 
2104 /*
2105  * Must be called with the queue_lock held.
2106  */
2107 static int cfqq_process_refs(struct cfq_queue *cfqq)
2108 {
2109         int process_refs, io_refs;
2110 
2111         io_refs = cfqq->allocated[READ] + cfqq->allocated[WRITE];
2112         process_refs = cfqq->ref - io_refs;
2113         BUG_ON(process_refs < 0);
2114         return process_refs;
2115 }
2116 
2117 static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq)
2118 {
2119         int process_refs, new_process_refs;
2120         struct cfq_queue *__cfqq;
2121 
2122         /*
2123          * If there are no process references on the new_cfqq, then it is
2124          * unsafe to follow the ->new_cfqq chain as other cfqq's in the
2125          * chain may have dropped their last reference (not just their
2126          * last process reference).
2127          */
2128         if (!cfqq_process_refs(new_cfqq))
2129                 return;
2130 
2131         /* Avoid a circular list and skip interim queue merges */
2132         while ((__cfqq = new_cfqq->new_cfqq)) {
2133                 if (__cfqq == cfqq)
2134                         return;
2135                 new_cfqq = __cfqq;
2136         }
2137 
2138         process_refs = cfqq_process_refs(cfqq);
2139         new_process_refs = cfqq_process_refs(new_cfqq);
2140         /*
2141          * If the process for the cfqq has gone away, there is no
2142          * sense in merging the queues.
2143          */
2144         if (process_refs == 0 || new_process_refs == 0)
2145                 return;
2146 
2147         /*
2148          * Merge in the direction of the lesser amount of work.
2149          */
2150         if (new_process_refs >= process_refs) {
2151                 cfqq->new_cfqq = new_cfqq;
2152                 new_cfqq->ref += process_refs;
2153         } else {
2154                 new_cfqq->new_cfqq = cfqq;
2155                 cfqq->ref += new_process_refs;
2156         }
2157 }
2158 
2159 static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd,
2160                                 struct cfq_group *cfqg, enum wl_prio_t prio)
2161 {
2162         struct cfq_queue *queue;
2163         int i;
2164         bool key_valid = false;
2165         unsigned long lowest_key = 0;
2166         enum wl_type_t cur_best = SYNC_NOIDLE_WORKLOAD;
2167 
2168         for (i = 0; i <= SYNC_WORKLOAD; ++i) {
2169                 /* select the one with lowest rb_key */
2170                 queue = cfq_rb_first(service_tree_for(cfqg, prio, i));
2171                 if (queue &&
2172                     (!key_valid || time_before(queue->rb_key, lowest_key))) {
2173                         lowest_key = queue->rb_key;
2174                         cur_best = i;
2175                         key_valid = true;
2176                 }
2177         }
2178 
2179         return cur_best;
2180 }
2181 
2182 static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
2183 {
2184         unsigned slice;
2185         unsigned count;
2186         struct cfq_rb_root *st;
2187         unsigned group_slice;
2188         enum wl_prio_t original_prio = cfqd->serving_prio;
2189 
2190         /* Choose next priority. RT > BE > IDLE */
2191         if (cfq_group_busy_queues_wl(RT_WORKLOAD, cfqd, cfqg))
2192                 cfqd->serving_prio = RT_WORKLOAD;
2193         else if (cfq_group_busy_queues_wl(BE_WORKLOAD, cfqd, cfqg))
2194                 cfqd->serving_prio = BE_WORKLOAD;
2195         else {
2196                 cfqd->serving_prio = IDLE_WORKLOAD;
2197                 cfqd->workload_expires = jiffies + 1;
2198                 return;
2199         }
2200 
2201         if (original_prio != cfqd->serving_prio)
2202                 goto new_workload;
2203 
2204         /*
2205          * For RT and BE, we have to choose also the type
2206          * (SYNC, SYNC_NOIDLE, ASYNC), and to compute a workload
2207          * expiration time
2208          */
2209         st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
2210         count = st->count;
2211 
2212         /*
2213          * check workload expiration, and that we still have other queues ready
2214          */
2215         if (count && !time_after(jiffies, cfqd->workload_expires))
2216                 return;
2217 
2218 new_workload:
2219         /* otherwise select new workload type */
2220         cfqd->serving_type =
2221                 cfq_choose_wl(cfqd, cfqg, cfqd->serving_prio);
2222         st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
2223         count = st->count;
2224 
2225         /*
2226          * the workload slice is computed as a fraction of target latency
2227          * proportional to the number of queues in that workload, over
2228          * all the queues in the same priority class
2229          */
2230         group_slice = cfq_group_slice(cfqd, cfqg);
2231 
2232         slice = group_slice * count /
2233                 max_t(unsigned, cfqg->busy_queues_avg[cfqd->serving_prio],
2234                       cfq_group_busy_queues_wl(cfqd->serving_prio, cfqd, cfqg));
2235 
2236         if (cfqd->serving_type == ASYNC_WORKLOAD) {
2237                 unsigned int tmp;
2238 
2239                 /*
2240                  * Async queues are currently system wide. Just taking
2241                  * proportion of queues with-in same group will lead to higher
2242                  * async ratio system wide as generally root group is going
2243                  * to have higher weight. A more accurate thing would be to
2244                  * calculate system wide asnc/sync ratio.
2245                  */
2246                 tmp = cfq_target_latency * cfqg_busy_async_queues(cfqd, cfqg);
2247                 tmp = tmp/cfqd->busy_queues;
2248                 slice = min_t(unsigned, slice, tmp);
2249 
2250                 /* async workload slice is scaled down according to
2251                  * the sync/async slice ratio. */
2252                 slice = slice * cfqd->cfq_slice[0] / cfqd->cfq_slice[1];
2253         } else
2254                 /* sync workload slice is at least 2 * cfq_slice_idle */
2255                 slice = max(slice, 2 * cfqd->cfq_slice_idle);
2256 
2257         slice = max_t(unsigned, slice, CFQ_MIN_TT);
2258         cfq_log(cfqd, "workload slice:%d", slice);
2259         cfqd->workload_expires = jiffies + slice;
2260 }
2261 
2262 static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
2263 {
2264         struct cfq_rb_root *st = &cfqd->grp_service_tree;
2265         struct cfq_group *cfqg;
2266 
2267         if (RB_EMPTY_ROOT(&st->rb))
2268                 return NULL;
2269         cfqg = cfq_rb_first_group(st);
2270         update_min_vdisktime(st);
2271         return cfqg;
2272 }
2273 
2274 static void cfq_choose_cfqg(struct cfq_data *cfqd)
2275 {
2276         struct cfq_group *cfqg = cfq_get_next_cfqg(cfqd);
2277 
2278         cfqd->serving_group = cfqg;
2279 
2280         /* Restore the workload type data */
2281         if (cfqg->saved_workload_slice) {
2282                 cfqd->workload_expires = jiffies + cfqg->saved_workload_slice;
2283                 cfqd->serving_type = cfqg->saved_workload;
2284                 cfqd->serving_prio = cfqg->saved_serving_prio;
2285         } else
2286                 cfqd->workload_expires = jiffies - 1;
2287 
2288         choose_service_tree(cfqd, cfqg);
2289 }
2290 
2291 /*
2292  * Select a queue for service. If we have a current active queue,
2293  * check whether to continue servicing it, or retrieve and set a new one.
2294  */
2295 static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
2296 {
2297         struct cfq_queue *cfqq, *new_cfqq = NULL;
2298 
2299         cfqq = cfqd->active_queue;
2300         if (!cfqq)
2301                 goto new_queue;
2302 
2303         if (!cfqd->rq_queued)
2304                 return NULL;
2305 
2306         /*
2307          * We were waiting for group to get backlogged. Expire the queue
2308          */
2309         if (cfq_cfqq_wait_busy(cfqq) && !RB_EMPTY_ROOT(&cfqq->sort_list))
2310                 goto expire;
2311 
2312         /*
2313          * The active queue has run out of time, expire it and select new.
2314          */
2315         if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq)) {
2316                 /*
2317                  * If slice had not expired at the completion of last request
2318                  * we might not have turned on wait_busy flag. Don't expire
2319                  * the queue yet. Allow the group to get backlogged.
2320                  *
2321                  * The very fact that we have used the slice, that means we
2322                  * have been idling all along on this queue and it should be
2323                  * ok to wait for this request to complete.
2324                  */
2325                 if (cfqq->cfqg->nr_cfqq == 1 && RB_EMPTY_ROOT(&cfqq->sort_list)
2326                     && cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
2327                         cfqq = NULL;
2328                         goto keep_queue;
2329                 } else
2330                         goto check_group_idle;
2331         }
2332 
2333         /*
2334          * The active queue has requests and isn't expired, allow it to
2335          * dispatch.
2336          */
2337         if (!RB_EMPTY_ROOT(&cfqq->sort_list))
2338                 goto keep_queue;
2339 
2340         /*
2341          * If another queue has a request waiting within our mean seek
2342          * distance, let it run.  The expire code will check for close
2343          * cooperators and put the close queue at the front of the service
2344          * tree.  If possible, merge the expiring queue with the new cfqq.
2345          */
2346         new_cfqq = cfq_close_cooperator(cfqd, cfqq);
2347         if (new_cfqq) {
2348                 if (!cfqq->new_cfqq)
2349                         cfq_setup_merge(cfqq, new_cfqq);
2350                 goto expire;
2351         }
2352 
2353         /*
2354          * No requests pending. If the active queue still has requests in
2355          * flight or is idling for a new request, allow either of these
2356          * conditions to happen (or time out) before selecting a new queue.
2357          */
2358         if (timer_pending(&cfqd->idle_slice_timer)) {
2359                 cfqq = NULL;
2360                 goto keep_queue;
2361         }
2362 
2363         /*
2364          * This is a deep seek queue, but the device is much faster than
2365          * the queue can deliver, don't idle
2366          **/
2367         if (CFQQ_SEEKY(cfqq) && cfq_cfqq_idle_window(cfqq) &&
2368             (cfq_cfqq_slice_new(cfqq) ||
2369             (cfqq->slice_end - jiffies > jiffies - cfqq->slice_start))) {
2370                 cfq_clear_cfqq_deep(cfqq);
2371                 cfq_clear_cfqq_idle_window(cfqq);
2372         }
2373 
2374         if (cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
2375                 cfqq = NULL;
2376                 goto keep_queue;
2377         }
2378 
2379         /*
2380          * If group idle is enabled and there are requests dispatched from
2381          * this group, wait for requests to complete.
2382          */
2383 check_group_idle:
2384         if (cfqd->cfq_group_idle && cfqq->cfqg->nr_cfqq == 1
2385             && cfqq->cfqg->dispatched) {
2386                 cfqq = NULL;
2387                 goto keep_queue;
2388         }
2389 
2390 expire:
2391         cfq_slice_expired(cfqd, 0);
2392 new_queue:
2393         /*
2394          * Current queue expired. Check if we have to switch to a new
2395          * service tree
2396          */
2397         if (!new_cfqq)
2398                 cfq_choose_cfqg(cfqd);
2399 
2400         cfqq = cfq_set_active_queue(cfqd, new_cfqq);
2401 keep_queue:
2402         return cfqq;
2403 }
2404 
2405 static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
2406 {
2407         int dispatched = 0;
2408 
2409         while (cfqq->next_rq) {
2410                 cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);
2411                 dispatched++;
2412         }
2413 
2414         BUG_ON(!list_empty(&cfqq->fifo));
2415 
2416         /* By default cfqq is not expired if it is empty. Do it explicitly */
2417         __cfq_slice_expired(cfqq->cfqd, cfqq, 0);
2418         return dispatched;
2419 }
2420 
2421 /*
2422  * Drain our current requests. Used for barriers and when switching
2423  * io schedulers on-the-fly.
2424  */
2425 static int cfq_forced_dispatch(struct cfq_data *cfqd)
2426 {
2427         struct cfq_queue *cfqq;
2428         int dispatched = 0;
2429 
2430         /* Expire the timeslice of the current active queue first */
2431         cfq_slice_expired(cfqd, 0);
2432         while ((cfqq = cfq_get_next_queue_forced(cfqd)) != NULL) {
2433                 __cfq_set_active_queue(cfqd, cfqq);
2434                 dispatched += __cfq_forced_dispatch_cfqq(cfqq);
2435         }
2436 
2437         BUG_ON(cfqd->busy_queues);
2438 
2439         cfq_log(cfqd, "forced_dispatch=%d", dispatched);
2440         return dispatched;
2441 }
2442 
2443 static inline bool cfq_slice_used_soon(struct cfq_data *cfqd,
2444         struct cfq_queue *cfqq)
2445 {
2446         /* the queue hasn't finished any request, can't estimate */
2447         if (cfq_cfqq_slice_new(cfqq))
2448                 return true;
2449         if (time_after(jiffies + cfqd->cfq_slice_idle * cfqq->dispatched,
2450                 cfqq->slice_end))
2451                 return true;
2452 
2453         return false;
2454 }
2455 
2456 static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
2457 {
2458         unsigned int max_dispatch;
2459 
2460         /*
2461          * Drain async requests before we start sync IO
2462          */
2463         if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_flight[BLK_RW_ASYNC])
2464                 return false;
2465 
2466         /*
2467          * If this is an async queue and we have sync IO in flight, let it wait
2468          */
2469         if (cfqd->rq_in_flight[BLK_RW_SYNC] && !cfq_cfqq_sync(cfqq))
2470                 return false;
2471 
2472         max_dispatch = max_t(unsigned int, cfqd->cfq_quantum / 2, 1);
2473         if (cfq_class_idle(cfqq))
2474                 max_dispatch = 1;
2475 
2476         /*
2477          * Does this cfqq already have too much IO in flight?
2478          */
2479         if (cfqq->dispatched >= max_dispatch) {
2480                 bool promote_sync = false;
2481                 /*
2482                  * idle queue must always only have a single IO in flight
2483                  */
2484                 if (cfq_class_idle(cfqq))
2485                         return false;
2486 
2487                 /*
2488                  * If there is only one sync queue
2489                  * we can ignore async queue here and give the sync
2490                  * queue no dispatch limit. The reason is a sync queue can
2491                  * preempt async queue, limiting the sync queue doesn't make
2492                  * sense. This is useful for aiostress test.
2493                  */
2494                 if (cfq_cfqq_sync(cfqq) && cfqd->busy_sync_queues == 1)
2495                         promote_sync = true;
2496 
2497                 /*
2498                  * We have other queues, don't allow more IO from this one
2499                  */
2500                 if (cfqd->busy_queues > 1 && cfq_slice_used_soon(cfqd, cfqq) &&
2501                                 !promote_sync)
2502                         return false;
2503 
2504                 /*
2505                  * Sole queue user, no limit
2506                  */
2507                 if (cfqd->busy_queues == 1 || promote_sync)
2508                         max_dispatch = -1;
2509                 else
2510                         /*
2511                          * Normally we start throttling cfqq when cfq_quantum/2
2512                          * requests have been dispatched. But we can drive
2513                          * deeper queue depths at the beginning of slice
2514                          * subjected to upper limit of cfq_quantum.
2515                          * */
2516                         max_dispatch = cfqd->cfq_quantum;
2517         }
2518 
2519         /*
2520          * Async queues must wait a bit before being allowed dispatch.
2521          * We also ramp up the dispatch depth gradually for async IO,
2522          * based on the last sync IO we serviced
2523          */
2524         if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_latency) {
2525                 unsigned long last_sync = jiffies - cfqd->last_delayed_sync;
2526                 unsigned int depth;
2527 
2528                 depth = last_sync / cfqd->cfq_slice[1];
2529                 if (!depth && !cfqq->dispatched)
2530                         depth = 1;
2531                 if (depth < max_dispatch)
2532                         max_dispatch = depth;
2533         }
2534 
2535         /*
2536          * If we're below the current max, allow a dispatch
2537          */
2538         return cfqq->dispatched < max_dispatch;
2539 }
2540 
2541 /*
2542  * Dispatch a request from cfqq, moving them to the request queue
2543  * dispatch list.
2544  */
2545 static bool cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
2546 {
2547         struct request *rq;
2548 
2549         BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
2550 
2551         if (!cfq_may_dispatch(cfqd, cfqq))
2552                 return false;
2553 
2554         /*
2555          * follow expired path, else get first next available
2556          */
2557         rq = cfq_check_fifo(cfqq);
2558         if (!rq)
2559                 rq = cfqq->next_rq;
2560 
2561         /*
2562          * insert request into driver dispatch list
2563          */
2564         cfq_dispatch_insert(cfqd->queue, rq);
2565 
2566         if (!cfqd->active_cic) {
2567                 struct cfq_io_context *cic = RQ_CIC(rq);
2568 
2569                 atomic_long_inc(&cic->ioc->refcount);
2570                 cfqd->active_cic = cic;
2571         }
2572 
2573         return true;
2574 }
2575 
2576 /*
2577  * Find the cfqq that we need to service and move a request from that to the
2578  * dispatch list
2579  */
2580 static int cfq_dispatch_requests(struct request_queue *q, int force)
2581 {
2582         struct cfq_data *cfqd = q->elevator->elevator_data;
2583         struct cfq_queue *cfqq;
2584 
2585         if (!cfqd->busy_queues)
2586                 return 0;
2587 
2588         if (unlikely(force))
2589                 return cfq_forced_dispatch(cfqd);
2590 
2591         cfqq = cfq_select_queue(cfqd);
2592         if (!cfqq)
2593                 return 0;
2594 
2595         /*
2596          * Dispatch a request from this cfqq, if it is allowed
2597          */
2598         if (!cfq_dispatch_request(cfqd, cfqq))
2599                 return 0;
2600 
2601         cfqq->slice_dispatch++;
2602         cfq_clear_cfqq_must_dispatch(cfqq);
2603 
2604         /*
2605          * expire an async queue immediately if it has used up its slice. idle
2606          * queue always expire after 1 dispatch round.
2607          */
2608         if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
2609             cfqq->slice_dispatch >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
2610             cfq_class_idle(cfqq))) {
2611                 cfqq->slice_end = jiffies + 1;
2612                 cfq_slice_expired(cfqd, 0);
2613         }
2614 
2615         cfq_log_cfqq(cfqd, cfqq, "dispatched a request");
2616         return 1;
2617 }
2618 
2619 /*
2620  * task holds one reference to the queue, dropped when task exits. each rq
2621  * in-flight on this queue also holds a reference, dropped when rq is freed.
2622  *
2623  * Each cfq queue took a reference on the parent group. Drop it now.
2624  * queue lock must be held here.
2625  */
2626 static void cfq_put_queue(struct cfq_queue *cfqq)
2627 {
2628         struct cfq_data *cfqd = cfqq->cfqd;
2629         struct cfq_group *cfqg;
2630 
2631         BUG_ON(cfqq->ref <= 0);
2632 
2633         cfqq->ref--;
2634         if (cfqq->ref)
2635                 return;
2636 
2637         cfq_log_cfqq(cfqd, cfqq, "put_queue");
2638         BUG_ON(rb_first(&cfqq->sort_list));
2639         BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
2640         cfqg = cfqq->cfqg;
2641 
2642         if (unlikely(cfqd->active_queue == cfqq)) {
2643                 __cfq_slice_expired(cfqd, cfqq, 0);
2644                 cfq_schedule_dispatch(cfqd);
2645         }
2646 
2647         BUG_ON(cfq_cfqq_on_rr(cfqq));
2648         kmem_cache_free(cfq_pool, cfqq);
2649         cfq_put_cfqg(cfqg);
2650 }
2651 
2652 /*
2653  * Call func for each cic attached to this ioc.
2654  */
2655 static void
2656 call_for_each_cic(struct io_context *ioc,
2657                   void (*func)(struct io_context *, struct cfq_io_context *))
2658 {
2659         struct cfq_io_context *cic;
2660         struct hlist_node *n;
2661 
2662         rcu_read_lock();
2663 
2664         hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
2665                 func(ioc, cic);
2666 
2667         rcu_read_unlock();
2668 }
2669 
2670 static void cfq_cic_free_rcu(struct rcu_head *head)
2671 {
2672         struct cfq_io_context *cic;
2673 
2674         cic = container_of(head, struct cfq_io_context, rcu_head);
2675 
2676         kmem_cache_free(cfq_ioc_pool, cic);
2677         elv_ioc_count_dec(cfq_ioc_count);
2678 
2679         if (ioc_gone) {
2680                 /*
2681                  * CFQ scheduler is exiting, grab exit lock and check
2682                  * the pending io context count. If it hits zero,
2683                  * complete ioc_gone and set it back to NULL
2684                  */
2685                 spin_lock(&ioc_gone_lock);
2686                 if (ioc_gone && !elv_ioc_count_read(cfq_ioc_count)) {
2687                         complete(ioc_gone);
2688                         ioc_gone = NULL;
2689                 }
2690                 spin_unlock(&ioc_gone_lock);
2691         }
2692 }
2693 
2694 static void cfq_cic_free(struct cfq_io_context *cic)
2695 {
2696         call_rcu(&cic->rcu_head, cfq_cic_free_rcu);
2697 }
2698 
2699 static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)
2700 {
2701         unsigned long flags;
2702         unsigned long dead_key = (unsigned long) cic->key;
2703 
2704         BUG_ON(!(dead_key & CIC_DEAD_KEY));
2705 
2706         spin_lock_irqsave(&ioc->lock, flags);
2707         radix_tree_delete(&ioc->radix_root, dead_key >> CIC_DEAD_INDEX_SHIFT);
2708         hlist_del_rcu(&cic->cic_list);
2709         spin_unlock_irqrestore(&ioc->lock, flags);
2710 
2711         cfq_cic_free(cic);
2712 }
2713 
2714 /*
2715  * Must be called with rcu_read_lock() held or preemption otherwise disabled.
2716  * Only two callers of this - ->dtor() which is called with the rcu_read_lock(),
2717  * and ->trim() which is called with the task lock held
2718  */
2719 static void cfq_free_io_context(struct io_context *ioc)
2720 {
2721         /*
2722          * ioc->refcount is zero here, or we are called from elv_unregister(),
2723          * so no more cic's are allowed to be linked into this ioc.  So it
2724          * should be ok to iterate over the known list, we will see all cic's
2725          * since no new ones are added.
2726          */
2727         call_for_each_cic(ioc, cic_free_func);
2728 }
2729 
2730 static void cfq_put_cooperator(struct cfq_queue *cfqq)
2731 {
2732         struct cfq_queue *__cfqq, *next;
2733 
2734         /*
2735          * If this queue was scheduled to merge with another queue, be
2736          * sure to drop the reference taken on that queue (and others in
2737          * the merge chain).  See cfq_setup_merge and cfq_merge_cfqqs.
2738          */
2739         __cfqq = cfqq->new_cfqq;
2740         while (__cfqq) {
2741                 if (__cfqq == cfqq) {
2742                         WARN(1, "cfqq->new_cfqq loop detected\n");
2743                         break;
2744                 }
2745                 next = __cfqq->new_cfqq;
2746                 cfq_put_queue(__cfqq);
2747                 __cfqq = next;
2748         }
2749 }
2750 
2751 static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
2752 {
2753         if (unlikely(cfqq == cfqd->active_queue)) {
2754                 __cfq_slice_expired(cfqd, cfqq, 0);
2755                 cfq_schedule_dispatch(cfqd);
2756         }
2757 
2758         cfq_put_cooperator(cfqq);
2759 
2760         cfq_put_queue(cfqq);
2761 }
2762 
2763 static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
2764                                          struct cfq_io_context *cic)
2765 {
2766         struct io_context *ioc = cic->ioc;
2767 
2768         list_del_init(&cic->queue_list);
2769 
2770         /*
2771          * Make sure dead mark is seen for dead queues
2772          */
2773         smp_wmb();
2774         cic->key = cfqd_dead_key(cfqd);
2775 
2776         rcu_read_lock();
2777         if (rcu_dereference(ioc->ioc_data) == cic) {
2778                 rcu_read_unlock();
2779                 spin_lock(&ioc->lock);
2780                 rcu_assign_pointer(ioc->ioc_data, NULL);
2781                 spin_unlock(&ioc->lock);
2782         } else
2783                 rcu_read_unlock();
2784 
2785         if (cic->cfqq[BLK_RW_ASYNC]) {
2786                 cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
2787                 cic->cfqq[BLK_RW_ASYNC] = NULL;
2788         }
2789 
2790         if (cic->cfqq[BLK_RW_SYNC]) {
2791                 cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_SYNC]);
2792                 cic->cfqq[BLK_RW_SYNC] = NULL;
2793         }
2794 }
2795 
2796 static void cfq_exit_single_io_context(struct io_context *ioc,
2797                                        struct cfq_io_context *cic)
2798 {
2799         struct cfq_data *cfqd = cic_to_cfqd(cic);
2800 
2801         if (cfqd) {
2802                 struct request_queue *q = cfqd->queue;
2803                 unsigned long flags;
2804 
2805                 spin_lock_irqsave(q->queue_lock, flags);
2806 
2807                 /*
2808                  * Ensure we get a fresh copy of the ->key to prevent
2809                  * race between exiting task and queue
2810                  */
2811                 smp_read_barrier_depends();
2812                 if (cic->key == cfqd)
2813                         __cfq_exit_single_io_context(cfqd, cic);
2814 
2815                 spin_unlock_irqrestore(q->queue_lock, flags);
2816         }
2817 }
2818 
2819 /*
2820  * The process that ioc belongs to has exited, we need to clean up
2821  * and put the internal structures we have that belongs to that process.
2822  */
2823 static void cfq_exit_io_context(struct io_context *ioc)
2824 {
2825         call_for_each_cic(ioc, cfq_exit_single_io_context);
2826 }
2827 
2828 static struct cfq_io_context *
2829 cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
2830 {
2831         struct cfq_io_context *cic;
2832 
2833         cic = kmem_cache_alloc_node(cfq_ioc_pool, gfp_mask | __GFP_ZERO,
2834                                                         cfqd->queue->node);
2835         if (cic) {
2836                 cic->last_end_request = jiffies;
2837                 INIT_LIST_HEAD(&cic->queue_list);
2838                 INIT_HLIST_NODE(&cic->cic_list);
2839                 cic->dtor = cfq_free_io_context;
2840                 cic->exit = cfq_exit_io_context;
2841                 elv_ioc_count_inc(cfq_ioc_count);
2842         }
2843 
2844         return cic;
2845 }
2846 
2847 static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
2848 {
2849         struct task_struct *tsk = current;
2850         int ioprio_class;
2851 
2852         if (!cfq_cfqq_prio_changed(cfqq))
2853                 return;
2854 
2855         ioprio_class = IOPRIO_PRIO_CLASS(ioc->ioprio);
2856         switch (ioprio_class) {
2857         default:
2858                 printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
2859         case IOPRIO_CLASS_NONE:
2860                 /*
2861                  * no prio set, inherit CPU scheduling settings
2862                  */
2863                 cfqq->ioprio = task_nice_ioprio(tsk);
2864                 cfqq->ioprio_class = task_nice_ioclass(tsk);
2865                 break;
2866         case IOPRIO_CLASS_RT:
2867                 cfqq->ioprio = task_ioprio(ioc);
2868                 cfqq->ioprio_class = IOPRIO_CLASS_RT;
2869                 break;
2870         case IOPRIO_CLASS_BE:
2871                 cfqq->ioprio = task_ioprio(ioc);
2872                 cfqq->ioprio_class = IOPRIO_CLASS_BE;
2873                 break;
2874         case IOPRIO_CLASS_IDLE:
2875                 cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
2876                 cfqq->ioprio = 7;
2877                 cfq_clear_cfqq_idle_window(cfqq);
2878                 break;
2879         }
2880 
2881         /*
2882          * keep track of original prio settings in case we have to temporarily
2883          * elevate the priority of this queue
2884          */
2885         cfqq->org_ioprio = cfqq->ioprio;
2886         cfqq->org_ioprio_class = cfqq->ioprio_class;
2887         cfq_clear_cfqq_prio_changed(cfqq);
2888 }
2889 
2890 static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
2891 {
2892         struct cfq_data *cfqd = cic_to_cfqd(cic);
2893         struct cfq_queue *cfqq;
2894         unsigned long flags;
2895 
2896         if (unlikely(!cfqd))
2897                 return;
2898 
2899         spin_lock_irqsave(cfqd->queue->queue_lock, flags);
2900 
2901         cfqq = cic->cfqq[BLK_RW_ASYNC];
2902         if (cfqq) {
2903                 struct cfq_queue *new_cfqq;
2904                 new_cfqq = cfq_get_queue(cfqd, BLK_RW_ASYNC, cic->ioc,
2905                                                 GFP_ATOMIC);
2906                 if (new_cfqq) {
2907                         cic->cfqq[BLK_RW_ASYNC] = new_cfqq;
2908                         cfq_put_queue(cfqq);
2909                 }
2910         }
2911 
2912         cfqq = cic->cfqq[BLK_RW_SYNC];
2913         if (cfqq)
2914                 cfq_mark_cfqq_prio_changed(cfqq);
2915 
2916         spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
2917 }
2918 
2919 static void cfq_ioc_set_ioprio(struct io_context *ioc)
2920 {
2921         call_for_each_cic(ioc, changed_ioprio);
2922         ioc->ioprio_changed = 0;
2923 }
2924 
2925 static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
2926                           pid_t pid, bool is_sync)
2927 {
2928         RB_CLEAR_NODE(&cfqq->rb_node);
2929         RB_CLEAR_NODE(&cfqq->p_node);
2930         INIT_LIST_HEAD(&cfqq->fifo);
2931 
2932         cfqq->ref = 0;
2933         cfqq->cfqd = cfqd;
2934 
2935         cfq_mark_cfqq_prio_changed(cfqq);
2936 
2937         if (is_sync) {
2938                 if (!cfq_class_idle(cfqq))
2939                         cfq_mark_cfqq_idle_window(cfqq);
2940                 cfq_mark_cfqq_sync(cfqq);
2941         }
2942         cfqq->pid = pid;
2943 }
2944 
2945 #ifdef CONFIG_CFQ_GROUP_IOSCHED
2946 static void changed_cgroup(struct io_context *ioc, struct cfq_io_context *cic)
2947 {
2948         struct cfq_queue *sync_cfqq = cic_to_cfqq(cic, 1);
2949         struct cfq_data *cfqd = cic_to_cfqd(cic);
2950         unsigned long flags;
2951         struct request_queue *q;
2952 
2953         if (unlikely(!cfqd))
2954                 return;
2955 
2956         q = cfqd->queue;
2957 
2958         spin_lock_irqsave(q->queue_lock, flags);
2959 
2960         if (sync_cfqq) {
2961                 /*
2962                  * Drop reference to sync queue. A new sync queue will be
2963                  * assigned in new group upon arrival of a fresh request.
2964                  */
2965                 cfq_log_cfqq(cfqd, sync_cfqq, "changed cgroup");
2966                 cic_set_cfqq(cic, NULL, 1);
2967                 cfq_put_queue(sync_cfqq);
2968         }
2969 
2970         spin_unlock_irqrestore(q->queue_lock, flags);
2971 }
2972 
2973 static void cfq_ioc_set_cgroup(struct io_context *ioc)
2974 {
2975         call_for_each_cic(ioc, changed_cgroup);
2976         ioc->cgroup_changed = 0;
2977 }
2978 #endif  /* CONFIG_CFQ_GROUP_IOSCHED */
2979 
2980 static struct cfq_queue *
2981 cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync,
2982                      struct io_context *ioc, gfp_t gfp_mask)
2983 {
2984         struct cfq_queue *cfqq, *new_cfqq = NULL;
2985         struct cfq_io_context *cic;
2986         struct cfq_group *cfqg;
2987 
2988 retry:
2989         cfqg = cfq_get_cfqg(cfqd);
2990         cic = cfq_cic_lookup(cfqd, ioc);
2991         /* cic always exists here */
2992         cfqq = cic_to_cfqq(cic, is_sync);
2993 
2994         /*
2995          * Always try a new alloc if we fell back to the OOM cfqq
2996          * originally, since it should just be a temporary situation.
2997          */
2998         if (!cfqq || cfqq == &cfqd->oom_cfqq) {
2999                 cfqq = NULL;
3000                 if (new_cfqq) {
3001                         cfqq = new_cfqq;
3002                         new_cfqq = NULL;
3003                 } else if (gfp_mask & __GFP_WAIT) {
3004                         spin_unlock_irq(cfqd->queue->queue_lock);
3005                         new_cfqq = kmem_cache_alloc_node(cfq_pool,
3006                                         gfp_mask | __GFP_ZERO,
3007                                         cfqd->queue->node);
3008                         spin_lock_irq(cfqd->queue->queue_lock);
3009                         if (new_cfqq)
3010                                 goto retry;
3011                 } else {
3012                         cfqq = kmem_cache_alloc_node(cfq_pool,
3013                                         gfp_mask | __GFP_ZERO,
3014                                         cfqd->queue->node);
3015                 }
3016 
3017                 if (cfqq) {
3018                         cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
3019                         cfq_init_prio_data(cfqq, ioc);
3020                         cfq_link_cfqq_cfqg(cfqq, cfqg);
3021                         cfq_log_cfqq(cfqd, cfqq, "alloced");
3022                 } else
3023                         cfqq = &cfqd->oom_cfqq;
3024         }
3025 
3026         if (new_cfqq)
3027                 kmem_cache_free(cfq_pool, new_cfqq);
3028 
3029         return cfqq;
3030 }
3031 
3032 static struct cfq_queue **
3033 cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
3034 {
3035         switch (ioprio_class) {
3036         case IOPRIO_CLASS_RT:
3037                 return &cfqd->async_cfqq[0][ioprio];
3038         case IOPRIO_CLASS_BE:
3039                 return &cfqd->async_cfqq[1][ioprio];
3040         case IOPRIO_CLASS_IDLE:
3041                 return &cfqd->async_idle_cfqq;
3042         default:
3043                 BUG();
3044         }
3045 }
3046 
3047 static struct cfq_queue *
3048 cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct io_context *ioc,
3049               gfp_t gfp_mask)
3050 {
3051         const int ioprio = task_ioprio(ioc);
3052         const int ioprio_class = task_ioprio_class(ioc);
3053         struct cfq_queue **async_cfqq = NULL;
3054         struct cfq_queue *cfqq = NULL;
3055 
3056         if (!is_sync) {
3057                 async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
3058                 cfqq = *async_cfqq;
3059         }
3060 
3061         if (!cfqq)
3062                 cfqq = cfq_find_alloc_queue(cfqd, is_sync, ioc, gfp_mask);
3063 
3064         /*
3065          * pin the queue now that it's allocated, scheduler exit will prune it
3066          */
3067         if (!is_sync && !(*async_cfqq)) {
3068                 cfqq->ref++;
3069                 *async_cfqq = cfqq;
3070         }
3071 
3072         cfqq->ref++;
3073         return cfqq;
3074 }
3075 
3076 /*
3077  * We drop cfq io contexts lazily, so we may find a dead one.
3078  */
3079 static void
3080 cfq_drop_dead_cic(struct cfq_data *cfqd, struct io_context *ioc,
3081                   struct cfq_io_context *cic)
3082 {
3083         unsigned long flags;
3084 
3085         WARN_ON(!list_empty(&cic->queue_list));
3086         BUG_ON(cic->key != cfqd_dead_key(cfqd));
3087 
3088         spin_lock_irqsave(&ioc->lock, flags);
3089 
3090         BUG_ON(rcu_dereference_check(ioc->ioc_data,
3091                 lockdep_is_held(&ioc->lock)) == cic);
3092 
3093         radix_tree_delete(&ioc->radix_root, cfqd->cic_index);
3094         hlist_del_rcu(&cic->cic_list);
3095         spin_unlock_irqrestore(&ioc->lock, flags);
3096 
3097         cfq_cic_free(cic);
3098 }
3099 
3100 static struct cfq_io_context *
3101 cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
3102 {
3103         struct cfq_io_context *cic;
3104         unsigned long flags;
3105 
3106         if (unlikely(!ioc))
3107                 return NULL;
3108 
3109         rcu_read_lock();
3110 
3111         /*
3112          * we maintain a last-hit cache, to avoid browsing over the tree
3113          */
3114         cic = rcu_dereference(ioc->ioc_data);
3115         if (cic && cic->key == cfqd) {
3116                 rcu_read_unlock();
3117                 return cic;
3118         }
3119 
3120         do {
3121                 cic = radix_tree_lookup(&ioc->radix_root, cfqd->cic_index);
3122                 rcu_read_unlock();
3123                 if (!cic)
3124                         break;
3125                 if (unlikely(cic->key != cfqd)) {
3126                         cfq_drop_dead_cic(cfqd, ioc, cic);
3127                         rcu_read_lock();
3128                         continue;
3129                 }
3130 
3131                 spin_lock_irqsave(&ioc->lock, flags);
3132                 rcu_assign_pointer(ioc->ioc_data, cic);
3133                 spin_unlock_irqrestore(&ioc->lock, flags);
3134                 break;
3135         } while (1);
3136 
3137         return cic;
3138 }
3139 
3140 /*
3141  * Add cic into ioc, using cfqd as the search key. This enables us to lookup
3142  * the process specific cfq io context when entered from the block layer.
3143  * Also adds the cic to a per-cfqd list, used when this queue is removed.
3144  */
3145 static int cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
3146                         struct cfq_io_context *cic, gfp_t gfp_mask)
3147 {
3148         unsigned long flags;
3149         int ret;
3150 
3151         ret = radix_tree_preload(gfp_mask);
3152         if (!ret) {
3153                 cic->ioc = ioc;
3154                 cic->key = cfqd;
3155 
3156                 spin_lock_irqsave(&ioc->lock, flags);
3157                 ret = radix_tree_insert(&ioc->radix_root,
3158                                                 cfqd->cic_index, cic);
3159                 if (!ret)
3160                         hlist_add_head_rcu(&cic->cic_list, &ioc->cic_list);
3161                 spin_unlock_irqrestore(&ioc->lock, flags);
3162 
3163                 radix_tree_preload_end();
3164 
3165                 if (!ret) {
3166                         spin_lock_irqsave(cfqd->queue->queue_lock, flags);
3167                         list_add(&cic->queue_list, &cfqd->cic_list);
3168                         spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
3169                 }
3170         }
3171 
3172         if (ret && ret != -EEXIST)
3173                 printk(KERN_ERR "cfq: cic link failed!\n");
3174 
3175         return ret;
3176 }
3177 
3178 /*
3179  * Setup general io context and cfq io context. There can be several cfq
3180  * io contexts per general io context, if this process is doing io to more
3181  * than one device managed by cfq.
3182  */
3183 static struct cfq_io_context *
3184 cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
3185 {
3186         struct io_context *ioc = NULL;
3187         struct cfq_io_context *cic;
3188         int ret;
3189 
3190         might_sleep_if(gfp_mask & __GFP_WAIT);
3191 
3192         ioc = get_io_context(gfp_mask, cfqd->queue->node);
3193         if (!ioc)
3194                 return NULL;
3195 
3196 retry:
3197         cic = cfq_cic_lookup(cfqd, ioc);
3198         if (cic)
3199                 goto out;
3200 
3201         cic = cfq_alloc_io_context(cfqd, gfp_mask);
3202         if (cic == NULL)
3203                 goto err;
3204 
3205         ret = cfq_cic_link(cfqd, ioc, cic, gfp_mask);
3206         if (ret == -EEXIST) {
3207                 /* someone has linked cic to ioc already */
3208                 cfq_cic_free(cic);
3209                 goto retry;
3210         } else if (ret)
3211                 goto err_free;
3212 
3213 out:
3214         smp_read_barrier_depends();
3215         if (unlikely(ioc->ioprio_changed))
3216                 cfq_ioc_set_ioprio(ioc);
3217 
3218 #ifdef CONFIG_CFQ_GROUP_IOSCHED
3219         if (unlikely(ioc->cgroup_changed))
3220                 cfq_ioc_set_cgroup(ioc);
3221 #endif
3222         return cic;
3223 err_free:
3224         cfq_cic_free(cic);
3225 err:
3226         put_io_context(ioc);
3227         return NULL;
3228 }
3229 
3230 static void
3231 cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)
3232 {
3233         unsigned long elapsed = jiffies - cic->last_end_request;
3234         unsigned long ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);
3235 
3236         cic->ttime_samples = (7*cic->ttime_samples + 256) / 8;
3237         cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8;
3238         cic->ttime_mean = (cic->ttime_total + 128) / cic->ttime_samples;
3239 }
3240 
3241 static void
3242 cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
3243                        struct request *rq)
3244 {
3245         sector_t sdist = 0;
3246         sector_t n_sec = blk_rq_sectors(rq);
3247         if (cfqq->last_request_pos) {
3248                 if (cfqq->last_request_pos < blk_rq_pos(rq))
3249                         sdist = blk_rq_pos(rq) - cfqq->last_request_pos;
3250                 else
3251                         sdist = cfqq->last_request_pos - blk_rq_pos(rq);
3252         }
3253 
3254         cfqq->seek_history <<= 1;
3255         if (blk_queue_nonrot(cfqd->queue))
3256                 cfqq->seek_history |= (n_sec < CFQQ_SECT_THR_NONROT);
3257         else
3258                 cfqq->seek_history |= (sdist > CFQQ_SEEK_THR);
3259 }
3260 
3261 /*
3262  * Disable idle window if the process thinks too long or seeks so much that
3263  * it doesn't matter
3264  */
3265 static void
3266 cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
3267                        struct cfq_io_context *cic)
3268 {
3269         int old_idle, enable_idle;
3270 
3271         /*
3272          * Don't idle for async or idle io prio class
3273          */
3274         if (!cfq_cfqq_sync(cfqq) || cfq_class_idle(cfqq))
3275                 return;
3276 
3277         enable_idle = old_idle = cfq_cfqq_idle_window(cfqq);
3278 
3279         if (cfqq->queued[0] + cfqq->queued[1] >= 4)
3280                 cfq_mark_cfqq_deep(cfqq);
3281 
3282         if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))
3283                 enable_idle = 0;
3284         else if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||
3285             (!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
3286                 enable_idle = 0;
3287         else if (sample_valid(cic->ttime_samples)) {
3288                 if (cic->ttime_mean > cfqd->cfq_slice_idle)
3289                         enable_idle = 0;
3290                 else
3291                         enable_idle = 1;
3292         }
3293 
3294         if (old_idle != enable_idle) {
3295                 cfq_log_cfqq(cfqd, cfqq, "idle=%d", enable_idle);
3296                 if (enable_idle)
3297                         cfq_mark_cfqq_idle_window(cfqq);
3298                 else
3299                         cfq_clear_cfqq_idle_window(cfqq);
3300         }
3301 }
3302 
3303 /*
3304  * Check if new_cfqq should preempt the currently active queue. Return 0 for
3305  * no or if we aren't sure, a 1 will cause a preempt.
3306  */
3307 static bool
3308 cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
3309                    struct request *rq)
3310 {
3311         struct cfq_queue *cfqq;
3312 
3313         cfqq = cfqd->active_queue;
3314         if (!cfqq)
3315                 return false;
3316 
3317         if (cfq_class_idle(new_cfqq))
3318                 return false;
3319 
3320         if (cfq_class_idle(cfqq))
3321                 return true;
3322 
3323         /*
3324          * Don't allow a non-RT request to preempt an ongoing RT cfqq timeslice.
3325          */
3326         if (cfq_class_rt(cfqq) && !cfq_class_rt(new_cfqq))
3327                 return false;
3328 
3329         /*
3330          * if the new request is sync, but the currently running queue is
3331          * not, let the sync request have priority.
3332          */
3333         if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
3334                 return true;
3335 
3336         if (new_cfqq->cfqg != cfqq->cfqg)
3337                 return false;
3338 
3339         if (cfq_slice_used(cfqq))
3340                 return true;
3341 
3342         /* Allow preemption only if we are idling on sync-noidle tree */
3343         if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
3344             cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
3345             new_cfqq->service_tree->count == 2 &&
3346             RB_EMPTY_ROOT(&cfqq->sort_list))
3347                 return true;
3348 
3349         /*
3350          * So both queues are sync. Let the new request get disk time if
3351          * it's a metadata request and the current queue is doing regular IO.
3352          */
3353         if ((rq->cmd_flags & REQ_META) && !cfqq->meta_pending)
3354                 return true;
3355 
3356         /*
3357          * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
3358          */
3359         if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
3360                 return true;
3361 
3362         /* An idle queue should not be idle now for some reason */
3363         if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq))
3364                 return true;
3365 
3366         if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
3367                 return false;
3368 
3369         /*
3370          * if this request is as-good as one we would expect from the
3371          * current cfqq, let it preempt
3372          */
3373         if (cfq_rq_close(cfqd, cfqq, rq))
3374                 return true;
3375 
3376         return false;
3377 }
3378 
3379 /*
3380  * cfqq preempts the active queue. if we allowed preempt with no slice left,
3381  * let it have half of its nominal slice.
3382  */
3383 static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
3384 {
3385         struct cfq_queue *old_cfqq = cfqd->active_queue;
3386 
3387         cfq_log_cfqq(cfqd, cfqq, "preempt");
3388         cfq_slice_expired(cfqd, 1);
3389 
3390         /*
3391          * workload type is changed, don't save slice, otherwise preempt
3392          * doesn't happen
3393          */
3394         if (cfqq_type(old_cfqq) != cfqq_type(cfqq))
3395                 cfqq->cfqg->saved_workload_slice = 0;
3396 
3397         /*
3398          * Put the new queue at the front of the of the current list,
3399          * so we know that it will be selected next.
3400          */
3401         BUG_ON(!cfq_cfqq_on_rr(cfqq));
3402 
3403         cfq_service_tree_add(cfqd, cfqq, 1);
3404 
3405         cfqq->slice_end = 0;
3406         cfq_mark_cfqq_slice_new(cfqq);
3407 }
3408 
3409 /*
3410  * Called when a new fs request (rq) is added (to cfqq). Check if there's
3411  * something we should do about it
3412  */
3413 static void
3414 cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
3415                 struct request *rq)
3416 {
3417         struct cfq_io_context *cic = RQ_CIC(rq);
3418 
3419         cfqd->rq_queued++;
3420         if (rq->cmd_flags & REQ_META)
3421                 cfqq->meta_pending++;
3422 
3423         cfq_update_io_thinktime(cfqd, cic);
3424         cfq_update_io_seektime(cfqd, cfqq, rq);
3425         cfq_update_idle_window(cfqd, cfqq, cic);
3426 
3427         cfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
3428 
3429         if (cfqq == cfqd->active_queue) {
3430                 /*
3431                  * Remember that we saw a request from this process, but
3432                  * don't start queuing just yet. Otherwise we risk seeing lots
3433                  * of tiny requests, because we disrupt the normal plugging
3434                  * and merging. If the request is already larger than a single
3435                  * page, let it rip immediately. For that case we assume that
3436                  * merging is already done. Ditto for a busy system that
3437                  * has other work pending, don't risk delaying until the
3438                  * idle timer unplug to continue working.
3439                  */
3440                 if (cfq_cfqq_wait_request(cfqq)) {
3441                         if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE ||
3442                             cfqd->busy_queues > 1) {
3443                                 cfq_del_timer(cfqd, cfqq);
3444                                 cfq_clear_cfqq_wait_request(cfqq);
3445                                 __blk_run_queue(cfqd->queue);
3446                         } else {
3447                                 cfq_blkiocg_update_idle_time_stats(
3448                                                 &cfqq->cfqg->blkg);
3449                                 cfq_mark_cfqq_must_dispatch(cfqq);
3450                         }
3451                 }
3452         } else if (cfq_should_preempt(cfqd, cfqq, rq)) {
3453                 /*
3454                  * not the active queue - expire current slice if it is
3455                  * idle and has expired it's mean thinktime or this new queue
3456                  * has some old slice time left and is of higher priority or
3457                  * this new queue is RT and the current one is BE
3458                  */
3459                 cfq_preempt_queue(cfqd, cfqq);
3460                 __blk_run_queue(cfqd->queue);
3461         }
3462 }
3463 
3464 static void cfq_insert_request(struct request_queue *q, struct request *rq)
3465 {
3466         struct cfq_data *cfqd = q->elevator->elevator_data;
3467         struct cfq_queue *cfqq = RQ_CFQQ(rq);
3468 
3469         cfq_log_cfqq(cfqd, cfqq, "insert_request");
3470         cfq_init_prio_data(cfqq, RQ_CIC(rq)->ioc);
3471 
3472         rq_set_fifo_time(rq, jiffies + cfqd->cfq_fifo_expire[rq_is_sync(rq)]);
3473         list_add_tail(&rq->queuelist, &cfqq->fifo);
3474         cfq_add_rq_rb(rq);
3475         cfq_blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,
3476                         &cfqd->serving_group->blkg, rq_data_dir(rq),
3477                         rq_is_sync(rq));
3478         cfq_rq_enqueued(cfqd, cfqq, rq);
3479 }
3480 
3481 /*
3482  * Update hw_tag based on peak queue depth over 50 samples under
3483  * sufficient load.
3484  */
3485 static void cfq_update_hw_tag(struct cfq_data *cfqd)
3486 {
3487         struct cfq_queue *cfqq = cfqd->active_queue;
3488 
3489         if (cfqd->rq_in_driver > cfqd->hw_tag_est_depth)
3490                 cfqd->hw_tag_est_depth = cfqd->rq_in_driver;
3491 
3492         if (cfqd->hw_tag == 1)
3493                 return;
3494 
3495         if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&
3496             cfqd->rq_in_driver <= CFQ_HW_QUEUE_MIN)
3497                 return;
3498 
3499         /*
3500          * If active queue hasn't enough requests and can idle, cfq might not
3501          * dispatch sufficient requests to hardware. Don't zero hw_tag in this
3502          * case
3503          */
3504         if (cfqq && cfq_cfqq_idle_window(cfqq) &&
3505             cfqq->dispatched + cfqq->queued[0] + cfqq->queued[1] <
3506             CFQ_HW_QUEUE_MIN && cfqd->rq_in_driver < CFQ_HW_QUEUE_MIN)
3507                 return;
3508 
3509         if (cfqd->hw_tag_samples++ < 50)
3510                 return;
3511 
3512         if (cfqd->hw_tag_est_depth >= CFQ_HW_QUEUE_MIN)
3513                 cfqd->hw_tag = 1;
3514         else
3515                 cfqd->hw_tag = 0;
3516 }
3517 
3518 static bool cfq_should_wait_busy(struct cfq_data *cfqd, struct cfq_queue *cfqq)
3519 {
3520         struct cfq_io_context *cic = cfqd->active_cic;
3521 
3522         /* If the queue already has requests, don't wait */
3523         if (!RB_EMPTY_ROOT(&cfqq->sort_list))
3524                 return false;
3525 
3526         /* If there are other queues in the group, don't wait */
3527         if (cfqq->cfqg->nr_cfqq > 1)
3528                 return false;
3529 
3530         if (cfq_slice_used(cfqq))
3531                 return true;
3532 
3533         /* if slice left is less than think time, wait busy */
3534         if (cic && sample_valid(cic->ttime_samples)
3535             && (cfqq->slice_end - jiffies < cic->ttime_mean))
3536                 return true;
3537 
3538         /*
3539          * If think times is less than a jiffy than ttime_mean=0 and above
3540          * will not be true. It might happen that slice has not expired yet
3541          * but will expire soon (4-5 ns) during select_queue(). To cover the
3542          * case where think time is less than a jiffy, mark the queue wait
3543          * busy if only 1 jiffy is left in the slice.
3544          */
3545         if (cfqq->slice_end - jiffies == 1)
3546                 return true;
3547 
3548         return false;
3549 }
3550 
3551 static void cfq_completed_request(struct request_queue *q, struct request *rq)
3552 {
3553         struct cfq_queue *cfqq = RQ_CFQQ(rq);
3554         struct cfq_data *cfqd = cfqq->cfqd;
3555         const int sync = rq_is_sync(rq);
3556         unsigned long now;
3557 
3558         now = jiffies;
3559         cfq_log_cfqq(cfqd, cfqq, "complete rqnoidle %d",
3560                      !!(rq->cmd_flags & REQ_NOIDLE));
3561 
3562         cfq_update_hw_tag(cfqd);
3563 
3564         WARN_ON(!cfqd->rq_in_driver);
3565         WARN_ON(!cfqq->dispatched);
3566         cfqd->rq_in_driver--;
3567         cfqq->dispatched--;
3568         (RQ_CFQG(rq))->dispatched--;
3569         cfq_blkiocg_update_completion_stats(&cfqq->cfqg->blkg,
3570                         rq_start_time_ns(rq), rq_io_start_time_ns(rq),
3571                         rq_data_dir(rq), rq_is_sync(rq));
3572 
3573         cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]--;
3574 
3575         if (sync) {
3576                 RQ_CIC(rq)->last_end_request = now;
3577                 if (!time_after(rq->start_time + cfqd->cfq_fifo_expire[1], now))
3578                         cfqd->last_delayed_sync = now;
3579         }
3580 
3581         /*
3582          * If this is the active queue, check if it needs to be expired,
3583          * or if we want to idle in case it has no pending requests.
3584          */
3585         if (cfqd->active_queue == cfqq) {
3586                 const bool cfqq_empty = RB_EMPTY_ROOT(&cfqq->sort_list);
3587 
3588                 if (cfq_cfqq_slice_new(cfqq)) {
3589                         cfq_set_prio_slice(cfqd, cfqq);
3590                         cfq_clear_cfqq_slice_new(cfqq);
3591                 }
3592 
3593                 /*
3594                  * Should we wait for next request to come in before we expire
3595                  * the queue.
3596                  */
3597                 if (cfq_should_wait_busy(cfqd, cfqq)) {
3598                         unsigned long extend_sl = cfqd->cfq_slice_idle;
3599                         if (!cfqd->cfq_slice_idle)
3600                                 extend_sl = cfqd->cfq_group_idle;
3601                         cfqq->slice_end = jiffies + extend_sl;
3602                         cfq_mark_cfqq_wait_busy(cfqq);
3603                         cfq_log_cfqq(cfqd, cfqq, "will busy wait");
3604                 }
3605 
3606                 /*
3607                  * Idling is not enabled on:
3608                  * - expired queues
3609                  * - idle-priority queues
3610                  * - async queues
3611                  * - queues with still some requests queued
3612                  * - when there is a close cooperator
3613                  */
3614                 if (cfq_slice_used(cfqq) || cfq_class_idle(cfqq))
3615                         cfq_slice_expired(cfqd, 1);
3616                 else if (sync && cfqq_empty &&
3617                          !cfq_close_cooperator(cfqd, cfqq)) {
3618                         cfq_arm_slice_timer(cfqd);
3619                 }
3620         }
3621 
3622         if (!cfqd->rq_in_driver)
3623                 cfq_schedule_dispatch(cfqd);
3624 }
3625 
3626 /*
3627  * we temporarily boost lower priority queues if they are holding fs exclusive
3628  * resources. they are boosted to normal prio (CLASS_BE/4)
3629  */
3630 static void cfq_prio_boost(struct cfq_queue *cfqq)
3631 {
3632         if (has_fs_excl()) {
3633                 /*
3634                  * boost idle prio on transactions that would lock out other
3635                  * users of the filesystem
3636                  */
3637                 if (cfq_class_idle(cfqq))
3638                         cfqq->ioprio_class = IOPRIO_CLASS_BE;
3639                 if (cfqq->ioprio > IOPRIO_NORM)
3640                         cfqq->ioprio = IOPRIO_NORM;
3641         } else {
3642                 /*
3643                  * unboost the queue (if needed)
3644                  */
3645                 cfqq->ioprio_class = cfqq->org_ioprio_class;
3646                 cfqq->ioprio = cfqq->org_ioprio;
3647         }
3648 }
3649 
3650 static inline int __cfq_may_queue(struct cfq_queue *cfqq)
3651 {
3652         if (cfq_cfqq_wait_request(cfqq) && !cfq_cfqq_must_alloc_slice(cfqq)) {
3653                 cfq_mark_cfqq_must_alloc_slice(cfqq);
3654                 return ELV_MQUEUE_MUST;
3655         }
3656 
3657         return ELV_MQUEUE_MAY;
3658 }
3659 
3660 static int cfq_may_queue(struct request_queue *q, int rw)
3661 {
3662         struct cfq_data *cfqd = q->elevator->elevator_data;
3663         struct task_struct *tsk = current;
3664         struct cfq_io_context *cic;
3665         struct cfq_queue *cfqq;
3666 
3667         /*
3668          * don't force setup of a queue from here, as a call to may_queue
3669          * does not necessarily imply that a request actually will be queued.
3670          * so just lookup a possibly existing queue, or return 'may queue'
3671          * if that fails
3672          */
3673         cic = cfq_cic_lookup(cfqd, tsk->io_context);
3674         if (!cic)
3675                 return ELV_MQUEUE_MAY;
3676 
3677         cfqq = cic_to_cfqq(cic, rw_is_sync(rw));
3678         if (cfqq) {
3679                 cfq_init_prio_data(cfqq, cic->ioc);
3680                 cfq_prio_boost(cfqq);
3681 
3682                 return __cfq_may_queue(cfqq);
3683         }
3684 
3685         return ELV_MQUEUE_MAY;
3686 }
3687 
3688 /*
3689  * queue lock held here
3690  */
3691 static void cfq_put_request(struct request *rq)
3692 {
3693         struct cfq_queue *cfqq = RQ_CFQQ(rq);
3694 
3695         if (cfqq) {
3696                 const int rw = rq_data_dir(rq);
3697 
3698                 BUG_ON(!cfqq->allocated[rw]);
3699                 cfqq->allocated[rw]--;
3700 
3701                 put_io_context(RQ_CIC(rq)->ioc);
3702 
3703                 rq->elevator_private[0] = NULL;
3704                 rq->elevator_private[1] = NULL;
3705 
3706                 /* Put down rq reference on cfqg */
3707                 cfq_put_cfqg(RQ_CFQG(rq));
3708                 rq->elevator_private[2] = NULL;
3709 
3710                 cfq_put_queue(cfqq);
3711         }
3712 }
3713 
3714 static struct cfq_queue *
3715 cfq_merge_cfqqs(struct cfq_data *cfqd, struct cfq_io_context *cic,
3716                 struct cfq_queue *cfqq)
3717 {
3718         cfq_log_cfqq(cfqd, cfqq, "merging with queue %p", cfqq->new_cfqq);
3719         cic_set_cfqq(cic, cfqq->new_cfqq, 1);
3720         cfq_mark_cfqq_coop(cfqq->new_cfqq);
3721         cfq_put_queue(cfqq);
3722         return cic_to_cfqq(cic, 1);
3723 }
3724 
3725 /*
3726  * Returns NULL if a new cfqq should be allocated, or the old cfqq if this
3727  * was the last process referring to said cfqq.
3728  */
3729 static struct cfq_queue *
3730 split_cfqq(struct cfq_io_context *cic, struct cfq_queue *cfqq)
3731 {
3732         if (cfqq_process_refs(cfqq) == 1) {
3733                 cfqq->pid = current->pid;
3734                 cfq_clear_cfqq_coop(cfqq);
3735                 cfq_clear_cfqq_split_coop(cfqq);
3736                 return cfqq;
3737         }
3738 
3739         cic_set_cfqq(cic, NULL, 1);
3740 
3741         cfq_put_cooperator(cfqq);
3742 
3743         cfq_put_queue(cfqq);
3744         return NULL;
3745 }
3746 /*
3747  * Allocate cfq data structures associated with this request.
3748  */
3749 static int
3750 cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
3751 {
3752         struct cfq_data *cfqd = q->elevator->elevator_data;
3753         struct cfq_io_context *cic;
3754         const int rw = rq_data_dir(rq);
3755         const bool is_sync = rq_is_sync(rq);
3756         struct cfq_queue *cfqq;
3757         unsigned long flags;
3758 
3759         might_sleep_if(gfp_mask & __GFP_WAIT);
3760 
3761         cic = cfq_get_io_context(cfqd, gfp_mask);
3762 
3763         spin_lock_irqsave(q->queue_lock, flags);
3764 
3765         if (!cic)
3766                 goto queue_fail;
3767 
3768 new_queue:
3769         cfqq = cic_to_cfqq(cic, is_sync);
3770         if (!cfqq || cfqq == &cfqd->oom_cfqq) {
3771                 cfqq = cfq_get_queue(cfqd, is_sync, cic->ioc, gfp_mask);
3772                 cic_set_cfqq(cic, cfqq, is_sync);
3773         } else {
3774                 /*
3775                  * If the queue was seeky for too long, break it apart.
3776                  */
3777                 if (cfq_cfqq_coop(cfqq) && cfq_cfqq_split_coop(cfqq)) {
3778                         cfq_log_cfqq(cfqd, cfqq, "breaking apart cfqq");
3779                         cfqq = split_cfqq(cic, cfqq);
3780                         if (!cfqq)
3781                                 goto new_queue;
3782                 }
3783 
3784                 /*
3785                  * Check to see if this queue is scheduled to merge with
3786                  * another, closely cooperating queue.  The merging of
3787                  * queues happens here as it must be done in process context.
3788                  * The reference on new_cfqq was taken in merge_cfqqs.
3789                  */
3790                 if (cfqq->new_cfqq)
3791                         cfqq = cfq_merge_cfqqs(cfqd, cic, cfqq);
3792         }
3793 
3794         cfqq->allocated[rw]++;
3795 
3796         cfqq->ref++;
3797         rq->elevator_private[0] = cic;
3798         rq->elevator_private[1] = cfqq;
3799         rq->elevator_private[2] = cfq_ref_get_cfqg(cfqq->cfqg);
3800         spin_unlock_irqrestore(q->queue_lock, flags);
3801         return 0;
3802 
3803 queue_fail:
3804         cfq_schedule_dispatch(cfqd);
3805         spin_unlock_irqrestore(q->queue_lock, flags);
3806         cfq_log(cfqd, "set_request fail");
3807         return 1;
3808 }
3809 
3810 static void cfq_kick_queue(struct work_struct *work)
3811 {
3812         struct cfq_data *cfqd =
3813                 container_of(work, struct cfq_data, unplug_work);
3814         struct request_queue *q = cfqd->queue;
3815 
3816         spin_lock_irq(q->queue_lock);
3817         __blk_run_queue(cfqd->queue);
3818         spin_unlock_irq(q->queue_lock);
3819 }
3820 
3821 /*
3822  * Timer running if the active_queue is currently idling inside its time slice
3823  */
3824 static void cfq_idle_slice_timer(unsigned long data)
3825 {
3826         struct cfq_data *cfqd = (struct cfq_data *) data;
3827         struct cfq_queue *cfqq;
3828         unsigned long flags;
3829         int timed_out = 1;
3830 
3831         cfq_log(cfqd, "idle timer fired");
3832 
3833         spin_lock_irqsave(cfqd->queue->queue_lock, flags);
3834 
3835         cfqq = cfqd->active_queue;
3836         if (cfqq) {
3837                 timed_out = 0;
3838 
3839                 /*
3840                  * We saw a request before the queue expired, let it through
3841                  */
3842                 if (cfq_cfqq_must_dispatch(cfqq))
3843                         goto out_kick;
3844 
3845                 /*
3846                  * expired
3847                  */
3848                 if (cfq_slice_used(cfqq))
3849                         goto expire;
3850 
3851                 /*
3852                  * only expire and reinvoke request handler, if there are
3853                  * other queues with pending requests
3854                  */
3855                 if (!cfqd->busy_queues)
3856                         goto out_cont;
3857 
3858                 /*
3859                  * not expired and it has a request pending, let it dispatch
3860                  */
3861                 if (!RB_EMPTY_ROOT(&cfqq->sort_list))
3862                         goto out_kick;
3863 
3864                 /*
3865                  * Queue depth flag is reset only when the idle didn't succeed
3866                  */
3867                 cfq_clear_cfqq_deep(cfqq);
3868         }
3869 expire:
3870         cfq_slice_expired(cfqd, timed_out);
3871 out_kick:
3872         cfq_schedule_dispatch(cfqd);
3873 out_cont:
3874         spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
3875 }
3876 
3877 static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
3878 {
3879         del_timer_sync(&cfqd->idle_slice_timer);
3880         cancel_work_sync(&cfqd->unplug_work);
3881 }
3882 
3883 static void cfq_put_async_queues(struct cfq_data *cfqd)
3884 {
3885         int i;
3886 
3887         for (i = 0; i < IOPRIO_BE_NR; i++) {
3888                 if (cfqd->async_cfqq[0][i])
3889                         cfq_put_queue(cfqd->async_cfqq[0][i]);
3890                 if (cfqd->async_cfqq[1][i])
3891                         cfq_put_queue(cfqd->async_cfqq[1][i]);
3892         }
3893 
3894         if (cfqd->async_idle_cfqq)
3895                 cfq_put_queue(cfqd->async_idle_cfqq);
3896 }
3897 
3898 static void cfq_exit_queue(struct elevator_queue *e)
3899 {
3900         struct cfq_data *cfqd = e->elevator_data;
3901         struct request_queue *q = cfqd->queue;
3902         bool wait = false;
3903 
3904         cfq_shutdown_timer_wq(cfqd);
3905 
3906         spin_lock_irq(q->queue_lock);
3907 
3908         if (cfqd->active_queue)
3909                 __cfq_slice_expired(cfqd, cfqd->active_queue, 0);
3910 
3911         while (!list_empty(&cfqd->cic_list)) {
3912                 struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
3913                                                         struct cfq_io_context,
3914                                                         queue_list);
3915 
3916                 __cfq_exit_single_io_context(cfqd, cic);
3917         }
3918 
3919         cfq_put_async_queues(cfqd);
3920         cfq_release_cfq_groups(cfqd);
3921 
3922         /*
3923          * If there are groups which we could not unlink from blkcg list,
3924          * wait for a rcu period for them to be freed.
3925          */
3926         if (cfqd->nr_blkcg_linked_grps)
3927                 wait = true;
3928 
3929         spin_unlock_irq(q->queue_lock);
3930 
3931         cfq_shutdown_timer_wq(cfqd);
3932 
3933         spin_lock(&cic_index_lock);
3934         ida_remove(&cic_index_ida, cfqd->cic_index);
3935         spin_unlock(&cic_index_lock);
3936 
3937         /*
3938          * Wait for cfqg->blkg->key accessors to exit their grace periods.
3939          * Do this wait only if there are other unlinked groups out
3940          * there. This can happen if cgroup deletion path claimed the
3941          * responsibility of cleaning up a group before queue cleanup code
3942          * get to the group.
3943          *
3944          * Do not call synchronize_rcu() unconditionally as there are drivers
3945          * which create/delete request queue hundreds of times during scan/boot
3946          * and synchronize_rcu() can take significant time and slow down boot.
3947          */
3948         if (wait)
3949                 synchronize_rcu();
3950 
3951 #ifdef CONFIG_CFQ_GROUP_IOSCHED
3952         /* Free up per cpu stats for root group */
3953         free_percpu(cfqd->root_group.blkg.stats_cpu);
3954 #endif
3955         kfree(cfqd);
3956 }
3957 
3958 static int cfq_alloc_cic_index(void)
3959 {
3960         int index, error;
3961 
3962         do {
3963                 if (!ida_pre_get(&cic_index_ida, GFP_KERNEL))
3964                         return -ENOMEM;
3965 
3966                 spin_lock(&cic_index_lock);
3967                 error = ida_get_new(&cic_index_ida, &index);
3968                 spin_unlock(&cic_index_lock);
3969                 if (error && error != -EAGAIN)
3970                         return error;
3971         } while (error);
3972 
3973         return index;
3974 }
3975 
3976 static void *cfq_init_queue(struct request_queue *q)
3977 {
3978         struct cfq_data *cfqd;
3979         int i, j;
3980         struct cfq_group *cfqg;
3981         struct cfq_rb_root *st;
3982 
3983         i = cfq_alloc_cic_index();
3984         if (i < 0)
3985                 return NULL;
3986 
3987         cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
3988         if (!cfqd) {
3989                 spin_lock(&cic_index_lock);
3990                 ida_remove(&cic_index_ida, i);
3991                 spin_unlock(&cic_index_lock);
3992                 return NULL;
3993         }
3994 
3995         /*
3996          * Don't need take queue_lock in the routine, since we are
3997          * initializing the ioscheduler, and nobody is using cfqd
3998          */
3999         cfqd->cic_index = i;
4000 
4001         /* Init root service tree */
4002         cfqd->grp_service_tree = CFQ_RB_ROOT;
4003 
4004         /* Init root group */
4005         cfqg = &cfqd->root_group;
4006         for_each_cfqg_st(cfqg, i, j, st)
4007                 *st = CFQ_RB_ROOT;
4008         RB_CLEAR_NODE(&cfqg->rb_node);
4009 
4010         /* Give preference to root group over other groups */
4011         cfqg->weight = 2*BLKIO_WEIGHT_DEFAULT;
4012 
4013 #ifdef CONFIG_CFQ_GROUP_IOSCHED
4014         /*
4015          * Set root group reference to 2. One reference will be dropped when
4016          * all groups on cfqd->cfqg_list are being deleted during queue exit.
4017          * Other reference will remain there as we don't want to delete this
4018          * group as it is statically allocated and gets destroyed when
4019          * throtl_data goes away.
4020          */
4021         cfqg->ref = 2;
4022 
4023         if (blkio_alloc_blkg_stats(&cfqg->blkg)) {
4024                 kfree(cfqg);
4025 
4026                 spin_lock(&cic_index_lock);
4027                 ida_remove(&cic_index_ida, cfqd->cic_index);
4028                 spin_unlock(&cic_index_lock);
4029 
4030                 kfree(cfqd);
4031                 return NULL;
4032         }
4033 
4034         rcu_read_lock();
4035 
4036         cfq_blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg,
4037                                         (void *)cfqd, 0);
4038         rcu_read_unlock();
4039         cfqd->nr_blkcg_linked_grps++;
4040 
4041         /* Add group on cfqd->cfqg_list */
4042         hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
4043 #endif
4044         /*
4045          * Not strictly needed (since RB_ROOT just clears the node and we
4046          * zeroed cfqd on alloc), but better be safe in case someone decides
4047          * to add magic to the rb code
4048          */
4049         for (i = 0; i < CFQ_PRIO_LISTS; i++)
4050                 cfqd->prio_trees[i] = RB_ROOT;
4051 
4052         /*
4053          * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
4054          * Grab a permanent reference to it, so that the normal code flow
4055          * will not attempt to free it.
4056          */
4057         cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0);
4058         cfqd->oom_cfqq.ref++;
4059         cfq_link_cfqq_cfqg(&cfqd->oom_cfqq, &cfqd->root_group);
4060 
4061         INIT_LIST_HEAD(&cfqd->cic_list);
4062 
4063         cfqd->queue = q;
4064 
4065         init_timer(&cfqd->idle_slice_timer);
4066         cfqd->idle_slice_timer.function = cfq_idle_slice_timer;
4067         cfqd->idle_slice_timer.data = (unsigned long) cfqd;
4068 
4069         INIT_WORK(&cfqd->unplug_work, cfq_kick_queue);
4070 
4071         cfqd->cfq_quantum = cfq_quantum;
4072         cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
4073         cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];
4074         cfqd->cfq_back_max = cfq_back_max;
4075         cfqd->cfq_back_penalty = cfq_back_penalty;
4076         cfqd->cfq_slice[0] = cfq_slice_async;
4077         cfqd->cfq_slice[1] = cfq_slice_sync;
4078         cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
4079         cfqd->cfq_slice_idle = cfq_slice_idle;
4080         cfqd->cfq_group_idle = cfq_group_idle;
4081         cfqd->cfq_latency = 1;
4082         cfqd->hw_tag = -1;
4083         /*
4084          * we optimistically start assuming sync ops weren't delayed in last
4085          * second, in order to have larger depth for async operations.
4086          */
4087         cfqd->last_delayed_sync = jiffies - HZ;
4088         return cfqd;
4089 }
4090 
4091 static void cfq_slab_kill(void)
4092 {
4093         /*
4094          * Caller already ensured that pending RCU callbacks are completed,
4095          * so we should have no busy allocations at this point.
4096          */
4097         if (cfq_pool)
4098                 kmem_cache_destroy(cfq_pool);
4099         if (cfq_ioc_pool)
4100                 kmem_cache_destroy(cfq_ioc_pool);
4101 }
4102 
4103 static int __init cfq_slab_setup(void)
4104 {
4105         cfq_pool = KMEM_CACHE(cfq_queue, 0);
4106         if (!cfq_pool)
4107                 goto fail;
4108 
4109         cfq_ioc_pool = KMEM_CACHE(cfq_io_context, 0);
4110         if (!cfq_ioc_pool)
4111                 goto fail;
4112 
4113         return 0;
4114 fail:
4115         cfq_slab_kill();
4116         return -ENOMEM;
4117 }
4118 
4119 /*
4120  * sysfs parts below -->
4121  */
4122 static ssize_t
4123 cfq_var_show(unsigned int var, char *page)
4124 {
4125         return sprintf(page, "%d\n", var);
4126 }
4127 
4128 static ssize_t
4129 cfq_var_store(unsigned int *var, const char *page, size_t count)
4130 {
4131         char *p = (char *) page;
4132 
4133         *var = simple_strtoul(p, &p, 10);
4134         return count;
4135 }
4136 
4137 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
4138 static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
4139 {                                                                       \
4140         struct cfq_data *cfqd = e->elevator_data;                       \
4141         unsigned int __data = __VAR;                                    \
4142         if (__CONV)                                                     \
4143                 __data = jiffies_to_msecs(__data);                      \
4144         return cfq_var_show(__data, (page));                            \
4145 }
4146 SHOW_FUNCTION(cfq_quantum_show, cfqd->cfq_quantum, 0);
4147 SHOW_FUNCTION(cfq_fifo_expire_sync_show, cfqd->cfq_fifo_expire[1], 1);
4148 SHOW_FUNCTION(cfq_fifo_expire_async_show, cfqd->cfq_fifo_expire[0], 1);
4149 SHOW_FUNCTION(cfq_back_seek_max_show, cfqd->cfq_back_max, 0);
4150 SHOW_FUNCTION(cfq_back_seek_penalty_show, cfqd->cfq_back_penalty, 0);
4151 SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
4152 SHOW_FUNCTION(cfq_group_idle_show, cfqd->cfq_group_idle, 1);
4153 SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
4154 SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
4155 SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
4156 SHOW_FUNCTION(cfq_low_latency_show, cfqd->cfq_latency, 0);
4157 #undef SHOW_FUNCTION
4158 
4159 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
4160 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
4161 {                                                                       \
4162         struct cfq_data *cfqd = e->elevator_data;                       \
4163         unsigned int __data;                                            \
4164         int ret = cfq_var_store(&__data, (page), count);                \
4165         if (__data < (MIN))                                             \
4166                 __data = (MIN);                                         \
4167         else if (__data > (MAX))                                        \
4168                 __data = (MAX);                                         \
4169         if (__CONV)                                                     \
4170                 *(__PTR) = msecs_to_jiffies(__data);                    \
4171         else                                                            \
4172                 *(__PTR) = __data;                                      \
4173         return ret;                                                     \
4174 }
4175 STORE_FUNCTION(cfq_quantum_store, &cfqd->cfq_quantum, 1, UINT_MAX, 0);
4176 STORE_FUNCTION(cfq_fifo_expire_sync_store, &cfqd->cfq_fifo_expire[1], 1,
4177                 UINT_MAX, 1);
4178 STORE_FUNCTION(cfq_fifo_expire_async_store, &cfqd->cfq_fifo_expire[0], 1,
4179                 UINT_MAX, 1);
4180 STORE_FUNCTION(cfq_back_seek_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
4181 STORE_FUNCTION(cfq_back_seek_penalty_store, &cfqd->cfq_back_penalty, 1,
4182                 UINT_MAX, 0);
4183 STORE_FUNCTION(cfq_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
4184 STORE_FUNCTION(cfq_group_idle_store, &cfqd->cfq_group_idle, 0, UINT_MAX, 1);
4185 STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
4186 STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
4187 STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1,
4188                 UINT_MAX, 0);
4189 STORE_FUNCTION(cfq_low_latency_store, &cfqd->cfq_latency, 0, 1, 0);
4190 #undef STORE_FUNCTION
4191 
4192 #define CFQ_ATTR(name) \
4193         __ATTR(name, S_IRUGO|S_IWUSR, cfq_##name##_show, cfq_##name##_store)
4194 
4195 static struct elv_fs_entry cfq_attrs[] = {
4196         CFQ_ATTR(quantum),
4197         CFQ_ATTR(fifo_expire_sync),
4198         CFQ_ATTR(fifo_expire_async),
4199         CFQ_ATTR(back_seek_max),
4200         CFQ_ATTR(back_seek_penalty),
4201         CFQ_ATTR(slice_sync),
4202         CFQ_ATTR(slice_async),
4203         CFQ_ATTR(slice_async_rq),
4204         CFQ_ATTR(slice_idle),
4205         CFQ_ATTR(group_idle),
4206         CFQ_ATTR(low_latency),
4207         __ATTR_NULL
4208 };
4209 
4210 static struct elevator_type iosched_cfq = {
4211         .ops = {
4212                 .elevator_merge_fn =            cfq_merge,
4213                 .elevator_merged_fn =           cfq_merged_request,
4214                 .elevator_merge_req_fn =        cfq_merged_requests,
4215                 .elevator_allow_merge_fn =      cfq_allow_merge,
4216                 .elevator_bio_merged_fn =       cfq_bio_merged,
4217                 .elevator_dispatch_fn =         cfq_dispatch_requests,
4218                 .elevator_add_req_fn =          cfq_insert_request,
4219                 .elevator_activate_req_fn =     cfq_activate_request,
4220                 .elevator_deactivate_req_fn =   cfq_deactivate_request,
4221                 .elevator_completed_req_fn =    cfq_completed_request,
4222                 .elevator_former_req_fn =       elv_rb_former_request,
4223                 .elevator_latter_req_fn =       elv_rb_latter_request,
4224                 .elevator_set_req_fn =          cfq_set_request,
4225                 .elevator_put_req_fn =          cfq_put_request,
4226                 .elevator_may_queue_fn =        cfq_may_queue,
4227                 .elevator_init_fn =             cfq_init_queue,
4228                 .elevator_exit_fn =             cfq_exit_queue,
4229                 .trim =                         cfq_free_io_context,
4230         },
4231         .elevator_attrs =       cfq_attrs,
4232         .elevator_name =        "cfq",
4233         .elevator_owner =       THIS_MODULE,
4234 };
4235 
4236 #ifdef CONFIG_CFQ_GROUP_IOSCHED
4237 static struct blkio_policy_type blkio_policy_cfq = {
4238         .ops = {
4239                 .blkio_unlink_group_fn =        cfq_unlink_blkio_group,
4240                 .blkio_update_group_weight_fn = cfq_update_blkio_group_weight,
4241         },
4242         .plid = BLKIO_POLICY_PROP,
4243 };
4244 #else
4245 static struct blkio_policy_type blkio_policy_cfq;
4246 #endif
4247 
4248 static int __init cfq_init(void)
4249 {
4250         /*
4251          * could be 0 on HZ < 1000 setups
4252          */
4253         if (!cfq_slice_async)
4254                 cfq_slice_async = 1;
4255         if (!cfq_slice_idle)
4256                 cfq_slice_idle = 1;
4257 
4258 #ifdef CONFIG_CFQ_GROUP_IOSCHED
4259         if (!cfq_group_idle)
4260                 cfq_group_idle = 1;
4261 #else
4262                 cfq_group_idle = 0;
4263 #endif
4264         if (cfq_slab_setup())
4265                 return -ENOMEM;
4266 
4267         elv_register(&iosched_cfq);
4268         blkio_policy_register(&blkio_policy_cfq);
4269 
4270         return 0;
4271 }
4272 
4273 static void __exit cfq_exit(void)
4274 {
4275         DECLARE_COMPLETION_ONSTACK(all_gone);
4276         blkio_policy_unregister(&blkio_policy_cfq);
4277         elv_unregister(&iosched_cfq);
4278         ioc_gone = &all_gone;
4279         /* ioc_gone's update must be visible before reading ioc_count */
4280         smp_wmb();
4281 
4282         /*
4283          * this also protects us from entering cfq_slab_kill() with
4284          * pending RCU callbacks
4285          */
4286         if (elv_ioc_count_read(cfq_ioc_count))
4287                 wait_for_completion(&all_gone);
4288         ida_destroy(&cic_index_ida);
4289         cfq_slab_kill();
4290 }
4291 
4292 module_init(cfq_init);
4293 module_exit(cfq_exit);
4294 
4295 MODULE_AUTHOR("Jens Axboe");
4296 MODULE_LICENSE("GPL");
4297 MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");
4298 

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