1 // SPDX-License-Identifier: GPL-2.0
3 * blk-mq scheduling framework
5 * Copyright (C) 2016 Jens Axboe
7 #include <linux/kernel.h>
8 #include <linux/module.h>
9 #include <linux/blk-mq.h>
10 #include <linux/list_sort.h>
12 #include <trace/events/block.h>
16 #include "blk-mq-debugfs.h"
17 #include "blk-mq-sched.h"
18 #include "blk-mq-tag.h"
21 void blk_mq_sched_assign_ioc(struct request *rq)
23 struct request_queue *q = rq->q;
24 struct io_context *ioc;
28 * May not have an IO context if it's a passthrough request
30 ioc = current->io_context;
34 spin_lock_irq(&q->queue_lock);
35 icq = ioc_lookup_icq(ioc, q);
36 spin_unlock_irq(&q->queue_lock);
39 icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
43 get_io_context(icq->ioc);
48 * Mark a hardware queue as needing a restart. For shared queues, maintain
49 * a count of how many hardware queues are marked for restart.
51 void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
53 if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
56 set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
58 EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
60 void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
62 if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
64 clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
67 * Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
68 * in blk_mq_run_hw_queue(). Its pair is the barrier in
69 * blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
70 * meantime new request added to hctx->dispatch is missed to check in
71 * blk_mq_run_hw_queue().
75 blk_mq_run_hw_queue(hctx, true);
78 static int sched_rq_cmp(void *priv, const struct list_head *a,
79 const struct list_head *b)
81 struct request *rqa = container_of(a, struct request, queuelist);
82 struct request *rqb = container_of(b, struct request, queuelist);
84 return rqa->mq_hctx > rqb->mq_hctx;
87 static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
89 struct blk_mq_hw_ctx *hctx =
90 list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
93 unsigned int count = 0;
95 list_for_each_entry(rq, rq_list, queuelist) {
96 if (rq->mq_hctx != hctx) {
97 list_cut_before(&hctx_list, rq_list, &rq->queuelist);
102 list_splice_tail_init(rq_list, &hctx_list);
105 return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
108 #define BLK_MQ_BUDGET_DELAY 3 /* ms units */
111 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
112 * its queue by itself in its completion handler, so we don't need to
113 * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
115 * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
116 * be run again. This is necessary to avoid starving flushes.
118 static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
120 struct request_queue *q = hctx->queue;
121 struct elevator_queue *e = q->elevator;
122 bool multi_hctxs = false, run_queue = false;
123 bool dispatched = false, busy = false;
124 unsigned int max_dispatch;
128 if (hctx->dispatch_busy)
131 max_dispatch = hctx->queue->nr_requests;
137 if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
140 if (!list_empty_careful(&hctx->dispatch)) {
145 budget_token = blk_mq_get_dispatch_budget(q);
146 if (budget_token < 0)
149 rq = e->type->ops.dispatch_request(hctx);
151 blk_mq_put_dispatch_budget(q, budget_token);
153 * We're releasing without dispatching. Holding the
154 * budget could have blocked any "hctx"s with the
155 * same queue and if we didn't dispatch then there's
156 * no guarantee anyone will kick the queue. Kick it
163 blk_mq_set_rq_budget_token(rq, budget_token);
166 * Now this rq owns the budget which has to be released
167 * if this rq won't be queued to driver via .queue_rq()
168 * in blk_mq_dispatch_rq_list().
170 list_add_tail(&rq->queuelist, &rq_list);
171 if (rq->mq_hctx != hctx)
173 } while (++count < max_dispatch);
177 blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
178 } else if (multi_hctxs) {
180 * Requests from different hctx may be dequeued from some
181 * schedulers, such as bfq and deadline.
183 * Sort the requests in the list according to their hctx,
184 * dispatch batching requests from same hctx at a time.
186 list_sort(NULL, &rq_list, sched_rq_cmp);
188 dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
189 } while (!list_empty(&rq_list));
191 dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
199 static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
204 ret = __blk_mq_do_dispatch_sched(hctx);
210 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
211 struct blk_mq_ctx *ctx)
213 unsigned short idx = ctx->index_hw[hctx->type];
215 if (++idx == hctx->nr_ctx)
218 return hctx->ctxs[idx];
222 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
223 * its queue by itself in its completion handler, so we don't need to
224 * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
226 * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
227 * be run again. This is necessary to avoid starving flushes.
229 static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
231 struct request_queue *q = hctx->queue;
233 struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
240 if (!list_empty_careful(&hctx->dispatch)) {
245 if (!sbitmap_any_bit_set(&hctx->ctx_map))
248 budget_token = blk_mq_get_dispatch_budget(q);
249 if (budget_token < 0)
252 rq = blk_mq_dequeue_from_ctx(hctx, ctx);
254 blk_mq_put_dispatch_budget(q, budget_token);
256 * We're releasing without dispatching. Holding the
257 * budget could have blocked any "hctx"s with the
258 * same queue and if we didn't dispatch then there's
259 * no guarantee anyone will kick the queue. Kick it
262 blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
266 blk_mq_set_rq_budget_token(rq, budget_token);
269 * Now this rq owns the budget which has to be released
270 * if this rq won't be queued to driver via .queue_rq()
271 * in blk_mq_dispatch_rq_list().
273 list_add(&rq->queuelist, &rq_list);
275 /* round robin for fair dispatch */
276 ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
278 } while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));
280 WRITE_ONCE(hctx->dispatch_from, ctx);
284 static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
286 struct request_queue *q = hctx->queue;
287 struct elevator_queue *e = q->elevator;
288 const bool has_sched_dispatch = e && e->type->ops.dispatch_request;
293 * If we have previous entries on our dispatch list, grab them first for
294 * more fair dispatch.
296 if (!list_empty_careful(&hctx->dispatch)) {
297 spin_lock(&hctx->lock);
298 if (!list_empty(&hctx->dispatch))
299 list_splice_init(&hctx->dispatch, &rq_list);
300 spin_unlock(&hctx->lock);
304 * Only ask the scheduler for requests, if we didn't have residual
305 * requests from the dispatch list. This is to avoid the case where
306 * we only ever dispatch a fraction of the requests available because
307 * of low device queue depth. Once we pull requests out of the IO
308 * scheduler, we can no longer merge or sort them. So it's best to
309 * leave them there for as long as we can. Mark the hw queue as
310 * needing a restart in that case.
312 * We want to dispatch from the scheduler if there was nothing
313 * on the dispatch list or we were able to dispatch from the
316 if (!list_empty(&rq_list)) {
317 blk_mq_sched_mark_restart_hctx(hctx);
318 if (blk_mq_dispatch_rq_list(hctx, &rq_list, 0)) {
319 if (has_sched_dispatch)
320 ret = blk_mq_do_dispatch_sched(hctx);
322 ret = blk_mq_do_dispatch_ctx(hctx);
324 } else if (has_sched_dispatch) {
325 ret = blk_mq_do_dispatch_sched(hctx);
326 } else if (hctx->dispatch_busy) {
327 /* dequeue request one by one from sw queue if queue is busy */
328 ret = blk_mq_do_dispatch_ctx(hctx);
330 blk_mq_flush_busy_ctxs(hctx, &rq_list);
331 blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
337 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
339 struct request_queue *q = hctx->queue;
341 /* RCU or SRCU read lock is needed before checking quiesced flag */
342 if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
348 * A return of -EAGAIN is an indication that hctx->dispatch is not
349 * empty and we must run again in order to avoid starving flushes.
351 if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
352 if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
353 blk_mq_run_hw_queue(hctx, true);
357 bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
358 unsigned int nr_segs)
360 struct elevator_queue *e = q->elevator;
361 struct blk_mq_ctx *ctx;
362 struct blk_mq_hw_ctx *hctx;
366 if (e && e->type->ops.bio_merge)
367 return e->type->ops.bio_merge(q, bio, nr_segs);
369 ctx = blk_mq_get_ctx(q);
370 hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
372 if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
373 list_empty_careful(&ctx->rq_lists[type]))
376 /* default per sw-queue merge */
377 spin_lock(&ctx->lock);
379 * Reverse check our software queue for entries that we could
380 * potentially merge with. Currently includes a hand-wavy stop
381 * count of 8, to not spend too much time checking for merges.
383 if (blk_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs)) {
388 spin_unlock(&ctx->lock);
393 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
395 return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
397 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
399 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
403 * dispatch flush and passthrough rq directly
405 * passthrough request has to be added to hctx->dispatch directly.
406 * For some reason, device may be in one situation which can't
407 * handle FS request, so STS_RESOURCE is always returned and the
408 * FS request will be added to hctx->dispatch. However passthrough
409 * request may be required at that time for fixing the problem. If
410 * passthrough request is added to scheduler queue, there isn't any
411 * chance to dispatch it given we prioritize requests in hctx->dispatch.
413 if ((rq->rq_flags & RQF_FLUSH_SEQ) || blk_rq_is_passthrough(rq))
419 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
420 bool run_queue, bool async)
422 struct request_queue *q = rq->q;
423 struct elevator_queue *e = q->elevator;
424 struct blk_mq_ctx *ctx = rq->mq_ctx;
425 struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
427 WARN_ON(e && (rq->tag != BLK_MQ_NO_TAG));
429 if (blk_mq_sched_bypass_insert(hctx, rq)) {
431 * Firstly normal IO request is inserted to scheduler queue or
432 * sw queue, meantime we add flush request to dispatch queue(
433 * hctx->dispatch) directly and there is at most one in-flight
434 * flush request for each hw queue, so it doesn't matter to add
435 * flush request to tail or front of the dispatch queue.
437 * Secondly in case of NCQ, flush request belongs to non-NCQ
438 * command, and queueing it will fail when there is any
439 * in-flight normal IO request(NCQ command). When adding flush
440 * rq to the front of hctx->dispatch, it is easier to introduce
441 * extra time to flush rq's latency because of S_SCHED_RESTART
442 * compared with adding to the tail of dispatch queue, then
443 * chance of flush merge is increased, and less flush requests
444 * will be issued to controller. It is observed that ~10% time
445 * is saved in blktests block/004 on disk attached to AHCI/NCQ
446 * drive when adding flush rq to the front of hctx->dispatch.
448 * Simply queue flush rq to the front of hctx->dispatch so that
449 * intensive flush workloads can benefit in case of NCQ HW.
451 at_head = (rq->rq_flags & RQF_FLUSH_SEQ) ? true : at_head;
452 blk_mq_request_bypass_insert(rq, at_head, false);
456 if (e && e->type->ops.insert_requests) {
459 list_add(&rq->queuelist, &list);
460 e->type->ops.insert_requests(hctx, &list, at_head);
462 spin_lock(&ctx->lock);
463 __blk_mq_insert_request(hctx, rq, at_head);
464 spin_unlock(&ctx->lock);
469 blk_mq_run_hw_queue(hctx, async);
472 void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
473 struct blk_mq_ctx *ctx,
474 struct list_head *list, bool run_queue_async)
476 struct elevator_queue *e;
477 struct request_queue *q = hctx->queue;
480 * blk_mq_sched_insert_requests() is called from flush plug
481 * context only, and hold one usage counter to prevent queue
482 * from being released.
484 percpu_ref_get(&q->q_usage_counter);
486 e = hctx->queue->elevator;
487 if (e && e->type->ops.insert_requests)
488 e->type->ops.insert_requests(hctx, list, false);
491 * try to issue requests directly if the hw queue isn't
492 * busy in case of 'none' scheduler, and this way may save
493 * us one extra enqueue & dequeue to sw queue.
495 if (!hctx->dispatch_busy && !e && !run_queue_async) {
496 blk_mq_try_issue_list_directly(hctx, list);
497 if (list_empty(list))
500 blk_mq_insert_requests(hctx, ctx, list);
503 blk_mq_run_hw_queue(hctx, run_queue_async);
505 percpu_ref_put(&q->q_usage_counter);
508 static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
509 struct blk_mq_hw_ctx *hctx,
510 unsigned int hctx_idx)
512 unsigned int flags = set->flags & ~BLK_MQ_F_TAG_HCTX_SHARED;
514 if (hctx->sched_tags) {
515 blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
516 blk_mq_free_rq_map(hctx->sched_tags, flags);
517 hctx->sched_tags = NULL;
521 static int blk_mq_sched_alloc_tags(struct request_queue *q,
522 struct blk_mq_hw_ctx *hctx,
523 unsigned int hctx_idx)
525 struct blk_mq_tag_set *set = q->tag_set;
526 /* Clear HCTX_SHARED so tags are init'ed */
527 unsigned int flags = set->flags & ~BLK_MQ_F_TAG_HCTX_SHARED;
530 hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
531 set->reserved_tags, flags);
532 if (!hctx->sched_tags)
535 ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
537 blk_mq_sched_free_tags(set, hctx, hctx_idx);
542 /* called in queue's release handler, tagset has gone away */
543 static void blk_mq_sched_tags_teardown(struct request_queue *q)
545 struct blk_mq_hw_ctx *hctx;
548 queue_for_each_hw_ctx(q, hctx, i) {
549 /* Clear HCTX_SHARED so tags are freed */
550 unsigned int flags = hctx->flags & ~BLK_MQ_F_TAG_HCTX_SHARED;
552 if (hctx->sched_tags) {
553 blk_mq_free_rq_map(hctx->sched_tags, flags);
554 hctx->sched_tags = NULL;
559 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
561 struct blk_mq_hw_ctx *hctx;
562 struct elevator_queue *eq;
568 q->nr_requests = q->tag_set->queue_depth;
573 * Default to double of smaller one between hw queue_depth and 128,
574 * since we don't split into sync/async like the old code did.
575 * Additionally, this is a per-hw queue depth.
577 q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
580 queue_for_each_hw_ctx(q, hctx, i) {
581 ret = blk_mq_sched_alloc_tags(q, hctx, i);
586 ret = e->ops.init_sched(q, e);
590 blk_mq_debugfs_register_sched(q);
592 queue_for_each_hw_ctx(q, hctx, i) {
593 if (e->ops.init_hctx) {
594 ret = e->ops.init_hctx(hctx, i);
597 blk_mq_sched_free_requests(q);
598 blk_mq_exit_sched(q, eq);
599 kobject_put(&eq->kobj);
603 blk_mq_debugfs_register_sched_hctx(q, hctx);
609 blk_mq_sched_free_requests(q);
610 blk_mq_sched_tags_teardown(q);
616 * called in either blk_queue_cleanup or elevator_switch, tagset
617 * is required for freeing requests
619 void blk_mq_sched_free_requests(struct request_queue *q)
621 struct blk_mq_hw_ctx *hctx;
624 queue_for_each_hw_ctx(q, hctx, i) {
625 if (hctx->sched_tags)
626 blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i);
630 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
632 struct blk_mq_hw_ctx *hctx;
635 queue_for_each_hw_ctx(q, hctx, i) {
636 blk_mq_debugfs_unregister_sched_hctx(hctx);
637 if (e->type->ops.exit_hctx && hctx->sched_data) {
638 e->type->ops.exit_hctx(hctx, i);
639 hctx->sched_data = NULL;
642 blk_mq_debugfs_unregister_sched(q);
643 if (e->type->ops.exit_sched)
644 e->type->ops.exit_sched(e);
645 blk_mq_sched_tags_teardown(q);