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

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * The Kyber I/O scheduler. Controls latency by throttling queue depths using
  4  * scalable techniques.
  5  *
  6  * Copyright (C) 2017 Facebook
  7  */
  8 
  9 #include <linux/kernel.h>
 10 #include <linux/blkdev.h>
 11 #include <linux/blk-mq.h>
 12 #include <linux/elevator.h>
 13 #include <linux/module.h>
 14 #include <linux/sbitmap.h>
 15 
 16 #include "blk.h"
 17 #include "blk-mq.h"
 18 #include "blk-mq-debugfs.h"
 19 #include "blk-mq-sched.h"
 20 #include "blk-mq-tag.h"
 21 
 22 #define CREATE_TRACE_POINTS
 23 #include <trace/events/kyber.h>
 24 
 25 /*
 26  * Scheduling domains: the device is divided into multiple domains based on the
 27  * request type.
 28  */
 29 enum {
 30         KYBER_READ,
 31         KYBER_WRITE,
 32         KYBER_DISCARD,
 33         KYBER_OTHER,
 34         KYBER_NUM_DOMAINS,
 35 };
 36 
 37 static const char *kyber_domain_names[] = {
 38         [KYBER_READ] = "READ",
 39         [KYBER_WRITE] = "WRITE",
 40         [KYBER_DISCARD] = "DISCARD",
 41         [KYBER_OTHER] = "OTHER",
 42 };
 43 
 44 enum {
 45         /*
 46          * In order to prevent starvation of synchronous requests by a flood of
 47          * asynchronous requests, we reserve 25% of requests for synchronous
 48          * operations.
 49          */
 50         KYBER_ASYNC_PERCENT = 75,
 51 };
 52 
 53 /*
 54  * Maximum device-wide depth for each scheduling domain.
 55  *
 56  * Even for fast devices with lots of tags like NVMe, you can saturate the
 57  * device with only a fraction of the maximum possible queue depth. So, we cap
 58  * these to a reasonable value.
 59  */
 60 static const unsigned int kyber_depth[] = {
 61         [KYBER_READ] = 256,
 62         [KYBER_WRITE] = 128,
 63         [KYBER_DISCARD] = 64,
 64         [KYBER_OTHER] = 16,
 65 };
 66 
 67 /*
 68  * Default latency targets for each scheduling domain.
 69  */
 70 static const u64 kyber_latency_targets[] = {
 71         [KYBER_READ] = 2ULL * NSEC_PER_MSEC,
 72         [KYBER_WRITE] = 10ULL * NSEC_PER_MSEC,
 73         [KYBER_DISCARD] = 5ULL * NSEC_PER_SEC,
 74 };
 75 
 76 /*
 77  * Batch size (number of requests we'll dispatch in a row) for each scheduling
 78  * domain.
 79  */
 80 static const unsigned int kyber_batch_size[] = {
 81         [KYBER_READ] = 16,
 82         [KYBER_WRITE] = 8,
 83         [KYBER_DISCARD] = 1,
 84         [KYBER_OTHER] = 1,
 85 };
 86 
 87 /*
 88  * Requests latencies are recorded in a histogram with buckets defined relative
 89  * to the target latency:
 90  *
 91  * <= 1/4 * target latency
 92  * <= 1/2 * target latency
 93  * <= 3/4 * target latency
 94  * <= target latency
 95  * <= 1 1/4 * target latency
 96  * <= 1 1/2 * target latency
 97  * <= 1 3/4 * target latency
 98  * > 1 3/4 * target latency
 99  */
100 enum {
101         /*
102          * The width of the latency histogram buckets is
103          * 1 / (1 << KYBER_LATENCY_SHIFT) * target latency.
104          */
105         KYBER_LATENCY_SHIFT = 2,
106         /*
107          * The first (1 << KYBER_LATENCY_SHIFT) buckets are <= target latency,
108          * thus, "good".
109          */
110         KYBER_GOOD_BUCKETS = 1 << KYBER_LATENCY_SHIFT,
111         /* There are also (1 << KYBER_LATENCY_SHIFT) "bad" buckets. */
112         KYBER_LATENCY_BUCKETS = 2 << KYBER_LATENCY_SHIFT,
113 };
114 
115 /*
116  * We measure both the total latency and the I/O latency (i.e., latency after
117  * submitting to the device).
118  */
119 enum {
120         KYBER_TOTAL_LATENCY,
121         KYBER_IO_LATENCY,
122 };
123 
124 static const char *kyber_latency_type_names[] = {
125         [KYBER_TOTAL_LATENCY] = "total",
126         [KYBER_IO_LATENCY] = "I/O",
127 };
128 
129 /*
130  * Per-cpu latency histograms: total latency and I/O latency for each scheduling
131  * domain except for KYBER_OTHER.
132  */
133 struct kyber_cpu_latency {
134         atomic_t buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
135 };
136 
137 /*
138  * There is a same mapping between ctx & hctx and kcq & khd,
139  * we use request->mq_ctx->index_hw to index the kcq in khd.
140  */
141 struct kyber_ctx_queue {
142         /*
143          * Used to ensure operations on rq_list and kcq_map to be an atmoic one.
144          * Also protect the rqs on rq_list when merge.
145          */
146         spinlock_t lock;
147         struct list_head rq_list[KYBER_NUM_DOMAINS];
148 } ____cacheline_aligned_in_smp;
149 
150 struct kyber_queue_data {
151         struct request_queue *q;
152 
153         /*
154          * Each scheduling domain has a limited number of in-flight requests
155          * device-wide, limited by these tokens.
156          */
157         struct sbitmap_queue domain_tokens[KYBER_NUM_DOMAINS];
158 
159         /*
160          * Async request percentage, converted to per-word depth for
161          * sbitmap_get_shallow().
162          */
163         unsigned int async_depth;
164 
165         struct kyber_cpu_latency __percpu *cpu_latency;
166 
167         /* Timer for stats aggregation and adjusting domain tokens. */
168         struct timer_list timer;
169 
170         unsigned int latency_buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
171 
172         unsigned long latency_timeout[KYBER_OTHER];
173 
174         int domain_p99[KYBER_OTHER];
175 
176         /* Target latencies in nanoseconds. */
177         u64 latency_targets[KYBER_OTHER];
178 };
179 
180 struct kyber_hctx_data {
181         spinlock_t lock;
182         struct list_head rqs[KYBER_NUM_DOMAINS];
183         unsigned int cur_domain;
184         unsigned int batching;
185         struct kyber_ctx_queue *kcqs;
186         struct sbitmap kcq_map[KYBER_NUM_DOMAINS];
187         struct sbq_wait domain_wait[KYBER_NUM_DOMAINS];
188         struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
189         atomic_t wait_index[KYBER_NUM_DOMAINS];
190 };
191 
192 static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
193                              void *key);
194 
195 static unsigned int kyber_sched_domain(unsigned int op)
196 {
197         switch (op & REQ_OP_MASK) {
198         case REQ_OP_READ:
199                 return KYBER_READ;
200         case REQ_OP_WRITE:
201                 return KYBER_WRITE;
202         case REQ_OP_DISCARD:
203                 return KYBER_DISCARD;
204         default:
205                 return KYBER_OTHER;
206         }
207 }
208 
209 static void flush_latency_buckets(struct kyber_queue_data *kqd,
210                                   struct kyber_cpu_latency *cpu_latency,
211                                   unsigned int sched_domain, unsigned int type)
212 {
213         unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
214         atomic_t *cpu_buckets = cpu_latency->buckets[sched_domain][type];
215         unsigned int bucket;
216 
217         for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
218                 buckets[bucket] += atomic_xchg(&cpu_buckets[bucket], 0);
219 }
220 
221 /*
222  * Calculate the histogram bucket with the given percentile rank, or -1 if there
223  * aren't enough samples yet.
224  */
225 static int calculate_percentile(struct kyber_queue_data *kqd,
226                                 unsigned int sched_domain, unsigned int type,
227                                 unsigned int percentile)
228 {
229         unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
230         unsigned int bucket, samples = 0, percentile_samples;
231 
232         for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
233                 samples += buckets[bucket];
234 
235         if (!samples)
236                 return -1;
237 
238         /*
239          * We do the calculation once we have 500 samples or one second passes
240          * since the first sample was recorded, whichever comes first.
241          */
242         if (!kqd->latency_timeout[sched_domain])
243                 kqd->latency_timeout[sched_domain] = max(jiffies + HZ, 1UL);
244         if (samples < 500 &&
245             time_is_after_jiffies(kqd->latency_timeout[sched_domain])) {
246                 return -1;
247         }
248         kqd->latency_timeout[sched_domain] = 0;
249 
250         percentile_samples = DIV_ROUND_UP(samples * percentile, 100);
251         for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS - 1; bucket++) {
252                 if (buckets[bucket] >= percentile_samples)
253                         break;
254                 percentile_samples -= buckets[bucket];
255         }
256         memset(buckets, 0, sizeof(kqd->latency_buckets[sched_domain][type]));
257 
258         trace_kyber_latency(kqd->q, kyber_domain_names[sched_domain],
259                             kyber_latency_type_names[type], percentile,
260                             bucket + 1, 1 << KYBER_LATENCY_SHIFT, samples);
261 
262         return bucket;
263 }
264 
265 static void kyber_resize_domain(struct kyber_queue_data *kqd,
266                                 unsigned int sched_domain, unsigned int depth)
267 {
268         depth = clamp(depth, 1U, kyber_depth[sched_domain]);
269         if (depth != kqd->domain_tokens[sched_domain].sb.depth) {
270                 sbitmap_queue_resize(&kqd->domain_tokens[sched_domain], depth);
271                 trace_kyber_adjust(kqd->q, kyber_domain_names[sched_domain],
272                                    depth);
273         }
274 }
275 
276 static void kyber_timer_fn(struct timer_list *t)
277 {
278         struct kyber_queue_data *kqd = from_timer(kqd, t, timer);
279         unsigned int sched_domain;
280         int cpu;
281         bool bad = false;
282 
283         /* Sum all of the per-cpu latency histograms. */
284         for_each_online_cpu(cpu) {
285                 struct kyber_cpu_latency *cpu_latency;
286 
287                 cpu_latency = per_cpu_ptr(kqd->cpu_latency, cpu);
288                 for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
289                         flush_latency_buckets(kqd, cpu_latency, sched_domain,
290                                               KYBER_TOTAL_LATENCY);
291                         flush_latency_buckets(kqd, cpu_latency, sched_domain,
292                                               KYBER_IO_LATENCY);
293                 }
294         }
295 
296         /*
297          * Check if any domains have a high I/O latency, which might indicate
298          * congestion in the device. Note that we use the p90; we don't want to
299          * be too sensitive to outliers here.
300          */
301         for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
302                 int p90;
303 
304                 p90 = calculate_percentile(kqd, sched_domain, KYBER_IO_LATENCY,
305                                            90);
306                 if (p90 >= KYBER_GOOD_BUCKETS)
307                         bad = true;
308         }
309 
310         /*
311          * Adjust the scheduling domain depths. If we determined that there was
312          * congestion, we throttle all domains with good latencies. Either way,
313          * we ease up on throttling domains with bad latencies.
314          */
315         for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
316                 unsigned int orig_depth, depth;
317                 int p99;
318 
319                 p99 = calculate_percentile(kqd, sched_domain,
320                                            KYBER_TOTAL_LATENCY, 99);
321                 /*
322                  * This is kind of subtle: different domains will not
323                  * necessarily have enough samples to calculate the latency
324                  * percentiles during the same window, so we have to remember
325                  * the p99 for the next time we observe congestion; once we do,
326                  * we don't want to throttle again until we get more data, so we
327                  * reset it to -1.
328                  */
329                 if (bad) {
330                         if (p99 < 0)
331                                 p99 = kqd->domain_p99[sched_domain];
332                         kqd->domain_p99[sched_domain] = -1;
333                 } else if (p99 >= 0) {
334                         kqd->domain_p99[sched_domain] = p99;
335                 }
336                 if (p99 < 0)
337                         continue;
338 
339                 /*
340                  * If this domain has bad latency, throttle less. Otherwise,
341                  * throttle more iff we determined that there is congestion.
342                  *
343                  * The new depth is scaled linearly with the p99 latency vs the
344                  * latency target. E.g., if the p99 is 3/4 of the target, then
345                  * we throttle down to 3/4 of the current depth, and if the p99
346                  * is 2x the target, then we double the depth.
347                  */
348                 if (bad || p99 >= KYBER_GOOD_BUCKETS) {
349                         orig_depth = kqd->domain_tokens[sched_domain].sb.depth;
350                         depth = (orig_depth * (p99 + 1)) >> KYBER_LATENCY_SHIFT;
351                         kyber_resize_domain(kqd, sched_domain, depth);
352                 }
353         }
354 }
355 
356 static unsigned int kyber_sched_tags_shift(struct request_queue *q)
357 {
358         /*
359          * All of the hardware queues have the same depth, so we can just grab
360          * the shift of the first one.
361          */
362         return q->queue_hw_ctx[0]->sched_tags->bitmap_tags.sb.shift;
363 }
364 
365 static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
366 {
367         struct kyber_queue_data *kqd;
368         unsigned int shift;
369         int ret = -ENOMEM;
370         int i;
371 
372         kqd = kzalloc_node(sizeof(*kqd), GFP_KERNEL, q->node);
373         if (!kqd)
374                 goto err;
375 
376         kqd->q = q;
377 
378         kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency,
379                                             GFP_KERNEL | __GFP_ZERO);
380         if (!kqd->cpu_latency)
381                 goto err_kqd;
382 
383         timer_setup(&kqd->timer, kyber_timer_fn, 0);
384 
385         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
386                 WARN_ON(!kyber_depth[i]);
387                 WARN_ON(!kyber_batch_size[i]);
388                 ret = sbitmap_queue_init_node(&kqd->domain_tokens[i],
389                                               kyber_depth[i], -1, false,
390                                               GFP_KERNEL, q->node);
391                 if (ret) {
392                         while (--i >= 0)
393                                 sbitmap_queue_free(&kqd->domain_tokens[i]);
394                         goto err_buckets;
395                 }
396         }
397 
398         for (i = 0; i < KYBER_OTHER; i++) {
399                 kqd->domain_p99[i] = -1;
400                 kqd->latency_targets[i] = kyber_latency_targets[i];
401         }
402 
403         shift = kyber_sched_tags_shift(q);
404         kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;
405 
406         return kqd;
407 
408 err_buckets:
409         free_percpu(kqd->cpu_latency);
410 err_kqd:
411         kfree(kqd);
412 err:
413         return ERR_PTR(ret);
414 }
415 
416 static int kyber_init_sched(struct request_queue *q, struct elevator_type *e)
417 {
418         struct kyber_queue_data *kqd;
419         struct elevator_queue *eq;
420 
421         eq = elevator_alloc(q, e);
422         if (!eq)
423                 return -ENOMEM;
424 
425         kqd = kyber_queue_data_alloc(q);
426         if (IS_ERR(kqd)) {
427                 kobject_put(&eq->kobj);
428                 return PTR_ERR(kqd);
429         }
430 
431         blk_stat_enable_accounting(q);
432 
433         eq->elevator_data = kqd;
434         q->elevator = eq;
435 
436         return 0;
437 }
438 
439 static void kyber_exit_sched(struct elevator_queue *e)
440 {
441         struct kyber_queue_data *kqd = e->elevator_data;
442         int i;
443 
444         del_timer_sync(&kqd->timer);
445 
446         for (i = 0; i < KYBER_NUM_DOMAINS; i++)
447                 sbitmap_queue_free(&kqd->domain_tokens[i]);
448         free_percpu(kqd->cpu_latency);
449         kfree(kqd);
450 }
451 
452 static void kyber_ctx_queue_init(struct kyber_ctx_queue *kcq)
453 {
454         unsigned int i;
455 
456         spin_lock_init(&kcq->lock);
457         for (i = 0; i < KYBER_NUM_DOMAINS; i++)
458                 INIT_LIST_HEAD(&kcq->rq_list[i]);
459 }
460 
461 static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
462 {
463         struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
464         struct kyber_hctx_data *khd;
465         int i;
466 
467         khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
468         if (!khd)
469                 return -ENOMEM;
470 
471         khd->kcqs = kmalloc_array_node(hctx->nr_ctx,
472                                        sizeof(struct kyber_ctx_queue),
473                                        GFP_KERNEL, hctx->numa_node);
474         if (!khd->kcqs)
475                 goto err_khd;
476 
477         for (i = 0; i < hctx->nr_ctx; i++)
478                 kyber_ctx_queue_init(&khd->kcqs[i]);
479 
480         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
481                 if (sbitmap_init_node(&khd->kcq_map[i], hctx->nr_ctx,
482                                       ilog2(8), GFP_KERNEL, hctx->numa_node)) {
483                         while (--i >= 0)
484                                 sbitmap_free(&khd->kcq_map[i]);
485                         goto err_kcqs;
486                 }
487         }
488 
489         spin_lock_init(&khd->lock);
490 
491         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
492                 INIT_LIST_HEAD(&khd->rqs[i]);
493                 khd->domain_wait[i].sbq = NULL;
494                 init_waitqueue_func_entry(&khd->domain_wait[i].wait,
495                                           kyber_domain_wake);
496                 khd->domain_wait[i].wait.private = hctx;
497                 INIT_LIST_HEAD(&khd->domain_wait[i].wait.entry);
498                 atomic_set(&khd->wait_index[i], 0);
499         }
500 
501         khd->cur_domain = 0;
502         khd->batching = 0;
503 
504         hctx->sched_data = khd;
505         sbitmap_queue_min_shallow_depth(&hctx->sched_tags->bitmap_tags,
506                                         kqd->async_depth);
507 
508         return 0;
509 
510 err_kcqs:
511         kfree(khd->kcqs);
512 err_khd:
513         kfree(khd);
514         return -ENOMEM;
515 }
516 
517 static void kyber_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
518 {
519         struct kyber_hctx_data *khd = hctx->sched_data;
520         int i;
521 
522         for (i = 0; i < KYBER_NUM_DOMAINS; i++)
523                 sbitmap_free(&khd->kcq_map[i]);
524         kfree(khd->kcqs);
525         kfree(hctx->sched_data);
526 }
527 
528 static int rq_get_domain_token(struct request *rq)
529 {
530         return (long)rq->elv.priv[0];
531 }
532 
533 static void rq_set_domain_token(struct request *rq, int token)
534 {
535         rq->elv.priv[0] = (void *)(long)token;
536 }
537 
538 static void rq_clear_domain_token(struct kyber_queue_data *kqd,
539                                   struct request *rq)
540 {
541         unsigned int sched_domain;
542         int nr;
543 
544         nr = rq_get_domain_token(rq);
545         if (nr != -1) {
546                 sched_domain = kyber_sched_domain(rq->cmd_flags);
547                 sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
548                                     rq->mq_ctx->cpu);
549         }
550 }
551 
552 static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
553 {
554         /*
555          * We use the scheduler tags as per-hardware queue queueing tokens.
556          * Async requests can be limited at this stage.
557          */
558         if (!op_is_sync(op)) {
559                 struct kyber_queue_data *kqd = data->q->elevator->elevator_data;
560 
561                 data->shallow_depth = kqd->async_depth;
562         }
563 }
564 
565 static bool kyber_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio,
566                 unsigned int nr_segs)
567 {
568         struct kyber_hctx_data *khd = hctx->sched_data;
569         struct blk_mq_ctx *ctx = blk_mq_get_ctx(hctx->queue);
570         struct kyber_ctx_queue *kcq = &khd->kcqs[ctx->index_hw[hctx->type]];
571         unsigned int sched_domain = kyber_sched_domain(bio->bi_opf);
572         struct list_head *rq_list = &kcq->rq_list[sched_domain];
573         bool merged;
574 
575         spin_lock(&kcq->lock);
576         merged = blk_mq_bio_list_merge(hctx->queue, rq_list, bio, nr_segs);
577         spin_unlock(&kcq->lock);
578 
579         return merged;
580 }
581 
582 static void kyber_prepare_request(struct request *rq, struct bio *bio)
583 {
584         rq_set_domain_token(rq, -1);
585 }
586 
587 static void kyber_insert_requests(struct blk_mq_hw_ctx *hctx,
588                                   struct list_head *rq_list, bool at_head)
589 {
590         struct kyber_hctx_data *khd = hctx->sched_data;
591         struct request *rq, *next;
592 
593         list_for_each_entry_safe(rq, next, rq_list, queuelist) {
594                 unsigned int sched_domain = kyber_sched_domain(rq->cmd_flags);
595                 struct kyber_ctx_queue *kcq = &khd->kcqs[rq->mq_ctx->index_hw[hctx->type]];
596                 struct list_head *head = &kcq->rq_list[sched_domain];
597 
598                 spin_lock(&kcq->lock);
599                 if (at_head)
600                         list_move(&rq->queuelist, head);
601                 else
602                         list_move_tail(&rq->queuelist, head);
603                 sbitmap_set_bit(&khd->kcq_map[sched_domain],
604                                 rq->mq_ctx->index_hw[hctx->type]);
605                 blk_mq_sched_request_inserted(rq);
606                 spin_unlock(&kcq->lock);
607         }
608 }
609 
610 static void kyber_finish_request(struct request *rq)
611 {
612         struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
613 
614         rq_clear_domain_token(kqd, rq);
615 }
616 
617 static void add_latency_sample(struct kyber_cpu_latency *cpu_latency,
618                                unsigned int sched_domain, unsigned int type,
619                                u64 target, u64 latency)
620 {
621         unsigned int bucket;
622         u64 divisor;
623 
624         if (latency > 0) {
625                 divisor = max_t(u64, target >> KYBER_LATENCY_SHIFT, 1);
626                 bucket = min_t(unsigned int, div64_u64(latency - 1, divisor),
627                                KYBER_LATENCY_BUCKETS - 1);
628         } else {
629                 bucket = 0;
630         }
631 
632         atomic_inc(&cpu_latency->buckets[sched_domain][type][bucket]);
633 }
634 
635 static void kyber_completed_request(struct request *rq, u64 now)
636 {
637         struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
638         struct kyber_cpu_latency *cpu_latency;
639         unsigned int sched_domain;
640         u64 target;
641 
642         sched_domain = kyber_sched_domain(rq->cmd_flags);
643         if (sched_domain == KYBER_OTHER)
644                 return;
645 
646         cpu_latency = get_cpu_ptr(kqd->cpu_latency);
647         target = kqd->latency_targets[sched_domain];
648         add_latency_sample(cpu_latency, sched_domain, KYBER_TOTAL_LATENCY,
649                            target, now - rq->start_time_ns);
650         add_latency_sample(cpu_latency, sched_domain, KYBER_IO_LATENCY, target,
651                            now - rq->io_start_time_ns);
652         put_cpu_ptr(kqd->cpu_latency);
653 
654         timer_reduce(&kqd->timer, jiffies + HZ / 10);
655 }
656 
657 struct flush_kcq_data {
658         struct kyber_hctx_data *khd;
659         unsigned int sched_domain;
660         struct list_head *list;
661 };
662 
663 static bool flush_busy_kcq(struct sbitmap *sb, unsigned int bitnr, void *data)
664 {
665         struct flush_kcq_data *flush_data = data;
666         struct kyber_ctx_queue *kcq = &flush_data->khd->kcqs[bitnr];
667 
668         spin_lock(&kcq->lock);
669         list_splice_tail_init(&kcq->rq_list[flush_data->sched_domain],
670                               flush_data->list);
671         sbitmap_clear_bit(sb, bitnr);
672         spin_unlock(&kcq->lock);
673 
674         return true;
675 }
676 
677 static void kyber_flush_busy_kcqs(struct kyber_hctx_data *khd,
678                                   unsigned int sched_domain,
679                                   struct list_head *list)
680 {
681         struct flush_kcq_data data = {
682                 .khd = khd,
683                 .sched_domain = sched_domain,
684                 .list = list,
685         };
686 
687         sbitmap_for_each_set(&khd->kcq_map[sched_domain],
688                              flush_busy_kcq, &data);
689 }
690 
691 static int kyber_domain_wake(wait_queue_entry_t *wqe, unsigned mode, int flags,
692                              void *key)
693 {
694         struct blk_mq_hw_ctx *hctx = READ_ONCE(wqe->private);
695         struct sbq_wait *wait = container_of(wqe, struct sbq_wait, wait);
696 
697         sbitmap_del_wait_queue(wait);
698         blk_mq_run_hw_queue(hctx, true);
699         return 1;
700 }
701 
702 static int kyber_get_domain_token(struct kyber_queue_data *kqd,
703                                   struct kyber_hctx_data *khd,
704                                   struct blk_mq_hw_ctx *hctx)
705 {
706         unsigned int sched_domain = khd->cur_domain;
707         struct sbitmap_queue *domain_tokens = &kqd->domain_tokens[sched_domain];
708         struct sbq_wait *wait = &khd->domain_wait[sched_domain];
709         struct sbq_wait_state *ws;
710         int nr;
711 
712         nr = __sbitmap_queue_get(domain_tokens);
713 
714         /*
715          * If we failed to get a domain token, make sure the hardware queue is
716          * run when one becomes available. Note that this is serialized on
717          * khd->lock, but we still need to be careful about the waker.
718          */
719         if (nr < 0 && list_empty_careful(&wait->wait.entry)) {
720                 ws = sbq_wait_ptr(domain_tokens,
721                                   &khd->wait_index[sched_domain]);
722                 khd->domain_ws[sched_domain] = ws;
723                 sbitmap_add_wait_queue(domain_tokens, ws, wait);
724 
725                 /*
726                  * Try again in case a token was freed before we got on the wait
727                  * queue.
728                  */
729                 nr = __sbitmap_queue_get(domain_tokens);
730         }
731 
732         /*
733          * If we got a token while we were on the wait queue, remove ourselves
734          * from the wait queue to ensure that all wake ups make forward
735          * progress. It's possible that the waker already deleted the entry
736          * between the !list_empty_careful() check and us grabbing the lock, but
737          * list_del_init() is okay with that.
738          */
739         if (nr >= 0 && !list_empty_careful(&wait->wait.entry)) {
740                 ws = khd->domain_ws[sched_domain];
741                 spin_lock_irq(&ws->wait.lock);
742                 sbitmap_del_wait_queue(wait);
743                 spin_unlock_irq(&ws->wait.lock);
744         }
745 
746         return nr;
747 }
748 
749 static struct request *
750 kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
751                           struct kyber_hctx_data *khd,
752                           struct blk_mq_hw_ctx *hctx)
753 {
754         struct list_head *rqs;
755         struct request *rq;
756         int nr;
757 
758         rqs = &khd->rqs[khd->cur_domain];
759 
760         /*
761          * If we already have a flushed request, then we just need to get a
762          * token for it. Otherwise, if there are pending requests in the kcqs,
763          * flush the kcqs, but only if we can get a token. If not, we should
764          * leave the requests in the kcqs so that they can be merged. Note that
765          * khd->lock serializes the flushes, so if we observed any bit set in
766          * the kcq_map, we will always get a request.
767          */
768         rq = list_first_entry_or_null(rqs, struct request, queuelist);
769         if (rq) {
770                 nr = kyber_get_domain_token(kqd, khd, hctx);
771                 if (nr >= 0) {
772                         khd->batching++;
773                         rq_set_domain_token(rq, nr);
774                         list_del_init(&rq->queuelist);
775                         return rq;
776                 } else {
777                         trace_kyber_throttled(kqd->q,
778                                               kyber_domain_names[khd->cur_domain]);
779                 }
780         } else if (sbitmap_any_bit_set(&khd->kcq_map[khd->cur_domain])) {
781                 nr = kyber_get_domain_token(kqd, khd, hctx);
782                 if (nr >= 0) {
783                         kyber_flush_busy_kcqs(khd, khd->cur_domain, rqs);
784                         rq = list_first_entry(rqs, struct request, queuelist);
785                         khd->batching++;
786                         rq_set_domain_token(rq, nr);
787                         list_del_init(&rq->queuelist);
788                         return rq;
789                 } else {
790                         trace_kyber_throttled(kqd->q,
791                                               kyber_domain_names[khd->cur_domain]);
792                 }
793         }
794 
795         /* There were either no pending requests or no tokens. */
796         return NULL;
797 }
798 
799 static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
800 {
801         struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
802         struct kyber_hctx_data *khd = hctx->sched_data;
803         struct request *rq;
804         int i;
805 
806         spin_lock(&khd->lock);
807 
808         /*
809          * First, if we are still entitled to batch, try to dispatch a request
810          * from the batch.
811          */
812         if (khd->batching < kyber_batch_size[khd->cur_domain]) {
813                 rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
814                 if (rq)
815                         goto out;
816         }
817 
818         /*
819          * Either,
820          * 1. We were no longer entitled to a batch.
821          * 2. The domain we were batching didn't have any requests.
822          * 3. The domain we were batching was out of tokens.
823          *
824          * Start another batch. Note that this wraps back around to the original
825          * domain if no other domains have requests or tokens.
826          */
827         khd->batching = 0;
828         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
829                 if (khd->cur_domain == KYBER_NUM_DOMAINS - 1)
830                         khd->cur_domain = 0;
831                 else
832                         khd->cur_domain++;
833 
834                 rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
835                 if (rq)
836                         goto out;
837         }
838 
839         rq = NULL;
840 out:
841         spin_unlock(&khd->lock);
842         return rq;
843 }
844 
845 static bool kyber_has_work(struct blk_mq_hw_ctx *hctx)
846 {
847         struct kyber_hctx_data *khd = hctx->sched_data;
848         int i;
849 
850         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
851                 if (!list_empty_careful(&khd->rqs[i]) ||
852                     sbitmap_any_bit_set(&khd->kcq_map[i]))
853                         return true;
854         }
855 
856         return false;
857 }
858 
859 #define KYBER_LAT_SHOW_STORE(domain, name)                              \
860 static ssize_t kyber_##name##_lat_show(struct elevator_queue *e,        \
861                                        char *page)                      \
862 {                                                                       \
863         struct kyber_queue_data *kqd = e->elevator_data;                \
864                                                                         \
865         return sprintf(page, "%llu\n", kqd->latency_targets[domain]);   \
866 }                                                                       \
867                                                                         \
868 static ssize_t kyber_##name##_lat_store(struct elevator_queue *e,       \
869                                         const char *page, size_t count) \
870 {                                                                       \
871         struct kyber_queue_data *kqd = e->elevator_data;                \
872         unsigned long long nsec;                                        \
873         int ret;                                                        \
874                                                                         \
875         ret = kstrtoull(page, 10, &nsec);                               \
876         if (ret)                                                        \
877                 return ret;                                             \
878                                                                         \
879         kqd->latency_targets[domain] = nsec;                            \
880                                                                         \
881         return count;                                                   \
882 }
883 KYBER_LAT_SHOW_STORE(KYBER_READ, read);
884 KYBER_LAT_SHOW_STORE(KYBER_WRITE, write);
885 #undef KYBER_LAT_SHOW_STORE
886 
887 #define KYBER_LAT_ATTR(op) __ATTR(op##_lat_nsec, 0644, kyber_##op##_lat_show, kyber_##op##_lat_store)
888 static struct elv_fs_entry kyber_sched_attrs[] = {
889         KYBER_LAT_ATTR(read),
890         KYBER_LAT_ATTR(write),
891         __ATTR_NULL
892 };
893 #undef KYBER_LAT_ATTR
894 
895 #ifdef CONFIG_BLK_DEBUG_FS
896 #define KYBER_DEBUGFS_DOMAIN_ATTRS(domain, name)                        \
897 static int kyber_##name##_tokens_show(void *data, struct seq_file *m)   \
898 {                                                                       \
899         struct request_queue *q = data;                                 \
900         struct kyber_queue_data *kqd = q->elevator->elevator_data;      \
901                                                                         \
902         sbitmap_queue_show(&kqd->domain_tokens[domain], m);             \
903         return 0;                                                       \
904 }                                                                       \
905                                                                         \
906 static void *kyber_##name##_rqs_start(struct seq_file *m, loff_t *pos)  \
907         __acquires(&khd->lock)                                          \
908 {                                                                       \
909         struct blk_mq_hw_ctx *hctx = m->private;                        \
910         struct kyber_hctx_data *khd = hctx->sched_data;                 \
911                                                                         \
912         spin_lock(&khd->lock);                                          \
913         return seq_list_start(&khd->rqs[domain], *pos);                 \
914 }                                                                       \
915                                                                         \
916 static void *kyber_##name##_rqs_next(struct seq_file *m, void *v,       \
917                                      loff_t *pos)                       \
918 {                                                                       \
919         struct blk_mq_hw_ctx *hctx = m->private;                        \
920         struct kyber_hctx_data *khd = hctx->sched_data;                 \
921                                                                         \
922         return seq_list_next(v, &khd->rqs[domain], pos);                \
923 }                                                                       \
924                                                                         \
925 static void kyber_##name##_rqs_stop(struct seq_file *m, void *v)        \
926         __releases(&khd->lock)                                          \
927 {                                                                       \
928         struct blk_mq_hw_ctx *hctx = m->private;                        \
929         struct kyber_hctx_data *khd = hctx->sched_data;                 \
930                                                                         \
931         spin_unlock(&khd->lock);                                        \
932 }                                                                       \
933                                                                         \
934 static const struct seq_operations kyber_##name##_rqs_seq_ops = {       \
935         .start  = kyber_##name##_rqs_start,                             \
936         .next   = kyber_##name##_rqs_next,                              \
937         .stop   = kyber_##name##_rqs_stop,                              \
938         .show   = blk_mq_debugfs_rq_show,                               \
939 };                                                                      \
940                                                                         \
941 static int kyber_##name##_waiting_show(void *data, struct seq_file *m)  \
942 {                                                                       \
943         struct blk_mq_hw_ctx *hctx = data;                              \
944         struct kyber_hctx_data *khd = hctx->sched_data;                 \
945         wait_queue_entry_t *wait = &khd->domain_wait[domain].wait;      \
946                                                                         \
947         seq_printf(m, "%d\n", !list_empty_careful(&wait->entry));       \
948         return 0;                                                       \
949 }
950 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_READ, read)
951 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_WRITE, write)
952 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_DISCARD, discard)
953 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_OTHER, other)
954 #undef KYBER_DEBUGFS_DOMAIN_ATTRS
955 
956 static int kyber_async_depth_show(void *data, struct seq_file *m)
957 {
958         struct request_queue *q = data;
959         struct kyber_queue_data *kqd = q->elevator->elevator_data;
960 
961         seq_printf(m, "%u\n", kqd->async_depth);
962         return 0;
963 }
964 
965 static int kyber_cur_domain_show(void *data, struct seq_file *m)
966 {
967         struct blk_mq_hw_ctx *hctx = data;
968         struct kyber_hctx_data *khd = hctx->sched_data;
969 
970         seq_printf(m, "%s\n", kyber_domain_names[khd->cur_domain]);
971         return 0;
972 }
973 
974 static int kyber_batching_show(void *data, struct seq_file *m)
975 {
976         struct blk_mq_hw_ctx *hctx = data;
977         struct kyber_hctx_data *khd = hctx->sched_data;
978 
979         seq_printf(m, "%u\n", khd->batching);
980         return 0;
981 }
982 
983 #define KYBER_QUEUE_DOMAIN_ATTRS(name)  \
984         {#name "_tokens", 0400, kyber_##name##_tokens_show}
985 static const struct blk_mq_debugfs_attr kyber_queue_debugfs_attrs[] = {
986         KYBER_QUEUE_DOMAIN_ATTRS(read),
987         KYBER_QUEUE_DOMAIN_ATTRS(write),
988         KYBER_QUEUE_DOMAIN_ATTRS(discard),
989         KYBER_QUEUE_DOMAIN_ATTRS(other),
990         {"async_depth", 0400, kyber_async_depth_show},
991         {},
992 };
993 #undef KYBER_QUEUE_DOMAIN_ATTRS
994 
995 #define KYBER_HCTX_DOMAIN_ATTRS(name)                                   \
996         {#name "_rqs", 0400, .seq_ops = &kyber_##name##_rqs_seq_ops},   \
997         {#name "_waiting", 0400, kyber_##name##_waiting_show}
998 static const struct blk_mq_debugfs_attr kyber_hctx_debugfs_attrs[] = {
999         KYBER_HCTX_DOMAIN_ATTRS(read),
1000         KYBER_HCTX_DOMAIN_ATTRS(write),
1001         KYBER_HCTX_DOMAIN_ATTRS(discard),
1002         KYBER_HCTX_DOMAIN_ATTRS(other),
1003         {"cur_domain", 0400, kyber_cur_domain_show},
1004         {"batching", 0400, kyber_batching_show},
1005         {},
1006 };
1007 #undef KYBER_HCTX_DOMAIN_ATTRS
1008 #endif
1009 
1010 static struct elevator_type kyber_sched = {
1011         .ops = {
1012                 .init_sched = kyber_init_sched,
1013                 .exit_sched = kyber_exit_sched,
1014                 .init_hctx = kyber_init_hctx,
1015                 .exit_hctx = kyber_exit_hctx,
1016                 .limit_depth = kyber_limit_depth,
1017                 .bio_merge = kyber_bio_merge,
1018                 .prepare_request = kyber_prepare_request,
1019                 .insert_requests = kyber_insert_requests,
1020                 .finish_request = kyber_finish_request,
1021                 .requeue_request = kyber_finish_request,
1022                 .completed_request = kyber_completed_request,
1023                 .dispatch_request = kyber_dispatch_request,
1024                 .has_work = kyber_has_work,
1025         },
1026 #ifdef CONFIG_BLK_DEBUG_FS
1027         .queue_debugfs_attrs = kyber_queue_debugfs_attrs,
1028         .hctx_debugfs_attrs = kyber_hctx_debugfs_attrs,
1029 #endif
1030         .elevator_attrs = kyber_sched_attrs,
1031         .elevator_name = "kyber",
1032         .elevator_owner = THIS_MODULE,
1033 };
1034 
1035 static int __init kyber_init(void)
1036 {
1037         return elv_register(&kyber_sched);
1038 }
1039 
1040 static void __exit kyber_exit(void)
1041 {
1042         elv_unregister(&kyber_sched);
1043 }
1044 
1045 module_init(kyber_init);
1046 module_exit(kyber_exit);
1047 
1048 MODULE_AUTHOR("Omar Sandoval");
1049 MODULE_LICENSE("GPL");
1050 MODULE_DESCRIPTION("Kyber I/O scheduler");
1051 

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