1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * blk-mq scheduling framework
4 *
5 * Copyright (C) 2016 Jens Axboe
6 */
7 #include <linux/kernel.h>
8 #include <linux/module.h>
9 #include <linux/list_sort.h>
10
11 #include <trace/events/block.h>
12
13 #include "blk.h"
14 #include "blk-mq.h"
15 #include "blk-mq-debugfs.h"
16 #include "blk-mq-sched.h"
17 #include "blk-wbt.h"
18
19 /*
20 * Mark a hardware queue as needing a restart.
21 */
22 void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
23 {
24 if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
25 return;
26
27 set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
28 }
29 EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
30
31 void __blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
32 {
33 clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
34
35 /*
36 * Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
37 * in blk_mq_run_hw_queue(). Its pair is the barrier in
38 * blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
39 * meantime new request added to hctx->dispatch is missed to check in
40 * blk_mq_run_hw_queue().
41 */
42 smp_mb();
43
44 blk_mq_run_hw_queue(hctx, true);
45 }
46
47 static int sched_rq_cmp(void *priv, const struct list_head *a,
48 const struct list_head *b)
49 {
50 struct request *rqa = container_of(a, struct request, queuelist);
51 struct request *rqb = container_of(b, struct request, queuelist);
52
53 return rqa->mq_hctx > rqb->mq_hctx;
54 }
55
56 static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
57 {
58 struct blk_mq_hw_ctx *hctx =
59 list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
60 struct request *rq;
61 LIST_HEAD(hctx_list);
62 unsigned int count = 0;
63
64 list_for_each_entry(rq, rq_list, queuelist) {
65 if (rq->mq_hctx != hctx) {
66 list_cut_before(&hctx_list, rq_list, &rq->queuelist);
67 goto dispatch;
68 }
69 count++;
70 }
71 list_splice_tail_init(rq_list, &hctx_list);
72
73 dispatch:
74 return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
75 }
76
77 #define BLK_MQ_BUDGET_DELAY 3 /* ms units */
78
79 /*
80 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
81 * its queue by itself in its completion handler, so we don't need to
82 * restart queue if .get_budget() fails to get the budget.
83 *
84 * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
85 * be run again. This is necessary to avoid starving flushes.
86 */
87 static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
88 {
89 struct request_queue *q = hctx->queue;
90 struct elevator_queue *e = q->elevator;
91 bool multi_hctxs = false, run_queue = false;
92 bool dispatched = false, busy = false;
93 unsigned int max_dispatch;
94 LIST_HEAD(rq_list);
95 int count = 0;
96
97 if (hctx->dispatch_busy)
98 max_dispatch = 1;
99 else
100 max_dispatch = hctx->queue->nr_requests;
101
102 do {
103 struct request *rq;
104 int budget_token;
105
106 if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
107 break;
108
109 if (!list_empty_careful(&hctx->dispatch)) {
110 busy = true;
111 break;
112 }
113
114 budget_token = blk_mq_get_dispatch_budget(q);
115 if (budget_token < 0)
116 break;
117
118 rq = e->type->ops.dispatch_request(hctx);
119 if (!rq) {
120 blk_mq_put_dispatch_budget(q, budget_token);
121 /*
122 * We're releasing without dispatching. Holding the
123 * budget could have blocked any "hctx"s with the
124 * same queue and if we didn't dispatch then there's
125 * no guarantee anyone will kick the queue. Kick it
126 * ourselves.
127 */
128 run_queue = true;
129 break;
130 }
131
132 blk_mq_set_rq_budget_token(rq, budget_token);
133
134 /*
135 * Now this rq owns the budget which has to be released
136 * if this rq won't be queued to driver via .queue_rq()
137 * in blk_mq_dispatch_rq_list().
138 */
139 list_add_tail(&rq->queuelist, &rq_list);
140 count++;
141 if (rq->mq_hctx != hctx)
142 multi_hctxs = true;
143
144 /*
145 * If we cannot get tag for the request, stop dequeueing
146 * requests from the IO scheduler. We are unlikely to be able
147 * to submit them anyway and it creates false impression for
148 * scheduling heuristics that the device can take more IO.
149 */
150 if (!blk_mq_get_driver_tag(rq))
151 break;
152 } while (count < max_dispatch);
153
154 if (!count) {
155 if (run_queue)
156 blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
157 } else if (multi_hctxs) {
158 /*
159 * Requests from different hctx may be dequeued from some
160 * schedulers, such as bfq and deadline.
161 *
162 * Sort the requests in the list according to their hctx,
163 * dispatch batching requests from same hctx at a time.
164 */
165 list_sort(NULL, &rq_list, sched_rq_cmp);
166 do {
167 dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
168 } while (!list_empty(&rq_list));
169 } else {
170 dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
171 }
172
173 if (busy)
174 return -EAGAIN;
175 return !!dispatched;
176 }
177
178 static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
179 {
180 unsigned long end = jiffies + HZ;
181 int ret;
182
183 do {
184 ret = __blk_mq_do_dispatch_sched(hctx);
185 if (ret != 1)
186 break;
187 if (need_resched() || time_is_before_jiffies(end)) {
188 blk_mq_delay_run_hw_queue(hctx, 0);
189 break;
190 }
191 } while (1);
192
193 return ret;
194 }
195
196 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
197 struct blk_mq_ctx *ctx)
198 {
199 unsigned short idx = ctx->index_hw[hctx->type];
200
201 if (++idx == hctx->nr_ctx)
202 idx = 0;
203
204 return hctx->ctxs[idx];
205 }
206
207 /*
208 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
209 * its queue by itself in its completion handler, so we don't need to
210 * restart queue if .get_budget() fails to get the budget.
211 *
212 * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
213 * be run again. This is necessary to avoid starving flushes.
214 */
215 static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
216 {
217 struct request_queue *q = hctx->queue;
218 LIST_HEAD(rq_list);
219 struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
220 int ret = 0;
221 struct request *rq;
222
223 do {
224 int budget_token;
225
226 if (!list_empty_careful(&hctx->dispatch)) {
227 ret = -EAGAIN;
228 break;
229 }
230
231 if (!sbitmap_any_bit_set(&hctx->ctx_map))
232 break;
233
234 budget_token = blk_mq_get_dispatch_budget(q);
235 if (budget_token < 0)
236 break;
237
238 rq = blk_mq_dequeue_from_ctx(hctx, ctx);
239 if (!rq) {
240 blk_mq_put_dispatch_budget(q, budget_token);
241 /*
242 * We're releasing without dispatching. Holding the
243 * budget could have blocked any "hctx"s with the
244 * same queue and if we didn't dispatch then there's
245 * no guarantee anyone will kick the queue. Kick it
246 * ourselves.
247 */
248 blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
249 break;
250 }
251
252 blk_mq_set_rq_budget_token(rq, budget_token);
253
254 /*
255 * Now this rq owns the budget which has to be released
256 * if this rq won't be queued to driver via .queue_rq()
257 * in blk_mq_dispatch_rq_list().
258 */
259 list_add(&rq->queuelist, &rq_list);
260
261 /* round robin for fair dispatch */
262 ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
263
264 } while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));
265
266 WRITE_ONCE(hctx->dispatch_from, ctx);
267 return ret;
268 }
269
270 static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
271 {
272 bool need_dispatch = false;
273 LIST_HEAD(rq_list);
274
275 /*
276 * If we have previous entries on our dispatch list, grab them first for
277 * more fair dispatch.
278 */
279 if (!list_empty_careful(&hctx->dispatch)) {
280 spin_lock(&hctx->lock);
281 if (!list_empty(&hctx->dispatch))
282 list_splice_init(&hctx->dispatch, &rq_list);
283 spin_unlock(&hctx->lock);
284 }
285
286 /*
287 * Only ask the scheduler for requests, if we didn't have residual
288 * requests from the dispatch list. This is to avoid the case where
289 * we only ever dispatch a fraction of the requests available because
290 * of low device queue depth. Once we pull requests out of the IO
291 * scheduler, we can no longer merge or sort them. So it's best to
292 * leave them there for as long as we can. Mark the hw queue as
293 * needing a restart in that case.
294 *
295 * We want to dispatch from the scheduler if there was nothing
296 * on the dispatch list or we were able to dispatch from the
297 * dispatch list.
298 */
299 if (!list_empty(&rq_list)) {
300 blk_mq_sched_mark_restart_hctx(hctx);
301 if (!blk_mq_dispatch_rq_list(hctx, &rq_list, 0))
302 return 0;
303 need_dispatch = true;
304 } else {
305 need_dispatch = hctx->dispatch_busy;
306 }
307
308 if (hctx->queue->elevator)
309 return blk_mq_do_dispatch_sched(hctx);
310
311 /* dequeue request one by one from sw queue if queue is busy */
312 if (need_dispatch)
313 return blk_mq_do_dispatch_ctx(hctx);
314 blk_mq_flush_busy_ctxs(hctx, &rq_list);
315 blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
316 return 0;
317 }
318
319 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
320 {
321 struct request_queue *q = hctx->queue;
322
323 /* RCU or SRCU read lock is needed before checking quiesced flag */
324 if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
325 return;
326
327 /*
328 * A return of -EAGAIN is an indication that hctx->dispatch is not
329 * empty and we must run again in order to avoid starving flushes.
330 */
331 if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
332 if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
333 blk_mq_run_hw_queue(hctx, true);
334 }
335 }
336
337 bool blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
338 unsigned int nr_segs)
339 {
340 struct elevator_queue *e = q->elevator;
341 struct blk_mq_ctx *ctx;
342 struct blk_mq_hw_ctx *hctx;
343 bool ret = false;
344 enum hctx_type type;
345
346 if (e && e->type->ops.bio_merge) {
347 ret = e->type->ops.bio_merge(q, bio, nr_segs);
348 goto out_put;
349 }
350
351 ctx = blk_mq_get_ctx(q);
352 hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
353 type = hctx->type;
354 if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
355 list_empty_careful(&ctx->rq_lists[type]))
356 goto out_put;
357
358 /* default per sw-queue merge */
359 spin_lock(&ctx->lock);
360 /*
361 * Reverse check our software queue for entries that we could
362 * potentially merge with. Currently includes a hand-wavy stop
363 * count of 8, to not spend too much time checking for merges.
364 */
365 if (blk_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs))
366 ret = true;
367
368 spin_unlock(&ctx->lock);
369 out_put:
370 return ret;
371 }
372
373 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq,
374 struct list_head *free)
375 {
376 return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free);
377 }
378 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
379
380 static int blk_mq_sched_alloc_map_and_rqs(struct request_queue *q,
381 struct blk_mq_hw_ctx *hctx,
382 unsigned int hctx_idx)
383 {
384 if (blk_mq_is_shared_tags(q->tag_set->flags)) {
385 hctx->sched_tags = q->sched_shared_tags;
386 return 0;
387 }
388
389 hctx->sched_tags = blk_mq_alloc_map_and_rqs(q->tag_set, hctx_idx,
390 q->nr_requests);
391
392 if (!hctx->sched_tags)
393 return -ENOMEM;
394 return 0;
395 }
396
397 static void blk_mq_exit_sched_shared_tags(struct request_queue *queue)
398 {
399 blk_mq_free_rq_map(queue->sched_shared_tags);
400 queue->sched_shared_tags = NULL;
401 }
402
403 /* called in queue's release handler, tagset has gone away */
404 static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int flags)
405 {
406 struct blk_mq_hw_ctx *hctx;
407 unsigned long i;
408
409 queue_for_each_hw_ctx(q, hctx, i) {
410 if (hctx->sched_tags) {
411 if (!blk_mq_is_shared_tags(flags))
412 blk_mq_free_rq_map(hctx->sched_tags);
413 hctx->sched_tags = NULL;
414 }
415 }
416
417 if (blk_mq_is_shared_tags(flags))
418 blk_mq_exit_sched_shared_tags(q);
419 }
420
421 static int blk_mq_init_sched_shared_tags(struct request_queue *queue)
422 {
423 struct blk_mq_tag_set *set = queue->tag_set;
424
425 /*
426 * Set initial depth at max so that we don't need to reallocate for
427 * updating nr_requests.
428 */
429 queue->sched_shared_tags = blk_mq_alloc_map_and_rqs(set,
430 BLK_MQ_NO_HCTX_IDX,
431 MAX_SCHED_RQ);
432 if (!queue->sched_shared_tags)
433 return -ENOMEM;
434
435 blk_mq_tag_update_sched_shared_tags(queue);
436
437 return 0;
438 }
439
440 /* caller must have a reference to @e, will grab another one if successful */
441 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
442 {
443 unsigned int flags = q->tag_set->flags;
444 struct blk_mq_hw_ctx *hctx;
445 struct elevator_queue *eq;
446 unsigned long i;
447 int ret;
448
449 /*
450 * Default to double of smaller one between hw queue_depth and 128,
451 * since we don't split into sync/async like the old code did.
452 * Additionally, this is a per-hw queue depth.
453 */
454 q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
455 BLKDEV_DEFAULT_RQ);
456
457 if (blk_mq_is_shared_tags(flags)) {
458 ret = blk_mq_init_sched_shared_tags(q);
459 if (ret)
460 return ret;
461 }
462
463 queue_for_each_hw_ctx(q, hctx, i) {
464 ret = blk_mq_sched_alloc_map_and_rqs(q, hctx, i);
465 if (ret)
466 goto err_free_map_and_rqs;
467 }
468
469 ret = e->ops.init_sched(q, e);
470 if (ret)
471 goto err_free_map_and_rqs;
472
473 mutex_lock(&q->debugfs_mutex);
474 blk_mq_debugfs_register_sched(q);
475 mutex_unlock(&q->debugfs_mutex);
476
477 queue_for_each_hw_ctx(q, hctx, i) {
478 if (e->ops.init_hctx) {
479 ret = e->ops.init_hctx(hctx, i);
480 if (ret) {
481 eq = q->elevator;
482 blk_mq_sched_free_rqs(q);
483 blk_mq_exit_sched(q, eq);
484 kobject_put(&eq->kobj);
485 return ret;
486 }
487 }
488 mutex_lock(&q->debugfs_mutex);
489 blk_mq_debugfs_register_sched_hctx(q, hctx);
490 mutex_unlock(&q->debugfs_mutex);
491 }
492
493 return 0;
494
495 err_free_map_and_rqs:
496 blk_mq_sched_free_rqs(q);
497 blk_mq_sched_tags_teardown(q, flags);
498
499 q->elevator = NULL;
500 return ret;
501 }
502
503 /*
504 * called in either blk_queue_cleanup or elevator_switch, tagset
505 * is required for freeing requests
506 */
507 void blk_mq_sched_free_rqs(struct request_queue *q)
508 {
509 struct blk_mq_hw_ctx *hctx;
510 unsigned long i;
511
512 if (blk_mq_is_shared_tags(q->tag_set->flags)) {
513 blk_mq_free_rqs(q->tag_set, q->sched_shared_tags,
514 BLK_MQ_NO_HCTX_IDX);
515 } else {
516 queue_for_each_hw_ctx(q, hctx, i) {
517 if (hctx->sched_tags)
518 blk_mq_free_rqs(q->tag_set,
519 hctx->sched_tags, i);
520 }
521 }
522 }
523
524 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
525 {
526 struct blk_mq_hw_ctx *hctx;
527 unsigned long i;
528 unsigned int flags = 0;
529
530 queue_for_each_hw_ctx(q, hctx, i) {
531 mutex_lock(&q->debugfs_mutex);
532 blk_mq_debugfs_unregister_sched_hctx(hctx);
533 mutex_unlock(&q->debugfs_mutex);
534
535 if (e->type->ops.exit_hctx && hctx->sched_data) {
536 e->type->ops.exit_hctx(hctx, i);
537 hctx->sched_data = NULL;
538 }
539 flags = hctx->flags;
540 }
541
542 mutex_lock(&q->debugfs_mutex);
543 blk_mq_debugfs_unregister_sched(q);
544 mutex_unlock(&q->debugfs_mutex);
545
546 if (e->type->ops.exit_sched)
547 e->type->ops.exit_sched(e);
548 blk_mq_sched_tags_teardown(q, flags);
549 q->elevator = NULL;
550 }
551
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