block/blk-mq-sched.c

   1 /*
   2  * blk-mq scheduling framework
   3  *
   4  * Copyright (C) 2016 Jens Axboe
   5  */
   6 #include <linux/kernel.h>
   7 #include <linux/module.h>
   8 #include <linux/blk-mq.h>
   9
  10 #include <trace/events/block.h>
  11
  12 #include "blk.h"
  13 #include "blk-mq.h"
  14 #include "blk-mq-debugfs.h"
  15 #include "blk-mq-sched.h"
  16 #include "blk-mq-tag.h"
  17 #include "blk-wbt.h"
  18
  19 void blk_mq_sched_free_hctx_data(struct request_queue *q,
  20                                  void (*exit)(struct blk_mq_hw_ctx *))
  21 {
  22         struct blk_mq_hw_ctx *hctx;
  23         int i;
  24
  25         queue_for_each_hw_ctx(q, hctx, i) {
  26                 if (exit && hctx->sched_data)
  27                         exit(hctx);
  28                 kfree(hctx->sched_data);
  29                 hctx->sched_data = NULL;
  30         }
  31 }
  32 EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
  33
  34 void blk_mq_sched_assign_ioc(struct request *rq, struct bio *bio)
  35 {
  36         struct request_queue *q = rq->q;
  37         struct io_context *ioc = rq_ioc(bio);
  38         struct io_cq *icq;
  39
  40         spin_lock_irq(q->queue_lock);
  41         icq = ioc_lookup_icq(ioc, q);
  42         spin_unlock_irq(q->queue_lock);
  43
  44         if (!icq) {
  45                 icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
  46                 if (!icq)
  47                         return;
  48         }
  49         get_io_context(icq->ioc);
  50         rq->elv.icq = icq;
  51 }
  52
  53 /*
  54  * Mark a hardware queue as needing a restart. For shared queues, maintain
  55  * a count of how many hardware queues are marked for restart.
  56  */
  57 static void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
  58 {
  59         if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  60                 return;
  61
  62         if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
  63                 struct request_queue *q = hctx->queue;
  64
  65                 if (!test_and_set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  66                         atomic_inc(&q->shared_hctx_restart);
  67         } else
  68                 set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  69 }
  70
  71 static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
  72 {
  73         if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  74                 return false;
  75
  76         if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
  77                 struct request_queue *q = hctx->queue;
  78
  79                 if (test_and_clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  80                         atomic_dec(&q->shared_hctx_restart);
  81         } else
  82                 clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  83
  84         return blk_mq_run_hw_queue(hctx, true);
  85 }
  86
  87 /*
  88  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
  89  * its queue by itself in its completion handler, so we don't need to
  90  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
  91  */
  92 static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
  93 {
  94         struct request_queue *q = hctx->queue;
  95         struct elevator_queue *e = q->elevator;
  96         LIST_HEAD(rq_list);
  97
  98         do {
  99                 struct request *rq;
 100
 101                 if (e->type->ops.mq.has_work &&
 102                                 !e->type->ops.mq.has_work(hctx))
 103                         break;
 104
 105                 if (!blk_mq_get_dispatch_budget(hctx))
 106                         break;
 107
 108                 rq = e->type->ops.mq.dispatch_request(hctx);
 109                 if (!rq) {
 110                         blk_mq_put_dispatch_budget(hctx);
 111                         break;
 112                 }
 113
 114                 /*
 115                  * Now this rq owns the budget which has to be released
 116                  * if this rq won't be queued to driver via .queue_rq()
 117                  * in blk_mq_dispatch_rq_list().
 118                  */
 119                 list_add(&rq->queuelist, &rq_list);
 120         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 121 }
 122
 123 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
 124                                           struct blk_mq_ctx *ctx)
 125 {
 126         unsigned idx = ctx->index_hw;
 127
 128         if (++idx == hctx->nr_ctx)
 129                 idx = 0;
 130
 131         return hctx->ctxs[idx];
 132 }
 133
 134 /*
 135  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 136  * its queue by itself in its completion handler, so we don't need to
 137  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
 138  */
 139 static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 140 {
 141         struct request_queue *q = hctx->queue;
 142         LIST_HEAD(rq_list);
 143         struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
 144
 145         do {
 146                 struct request *rq;
 147
 148                 if (!sbitmap_any_bit_set(&hctx->ctx_map))
 149                         break;
 150
 151                 if (!blk_mq_get_dispatch_budget(hctx))
 152                         break;
 153
 154                 rq = blk_mq_dequeue_from_ctx(hctx, ctx);
 155                 if (!rq) {
 156                         blk_mq_put_dispatch_budget(hctx);
 157                         break;
 158                 }
 159
 160                 /*
 161                  * Now this rq owns the budget which has to be released
 162                  * if this rq won't be queued to driver via .queue_rq()
 163                  * in blk_mq_dispatch_rq_list().
 164                  */
 165                 list_add(&rq->queuelist, &rq_list);
 166
 167                 /* round robin for fair dispatch */
 168                 ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
 169
 170         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 171
 172         WRITE_ONCE(hctx->dispatch_from, ctx);
 173 }
 174
 175 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 176 {
 177         struct request_queue *q = hctx->queue;
 178         struct elevator_queue *e = q->elevator;
 179         const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
 180         LIST_HEAD(rq_list);
 181
 182         /* RCU or SRCU read lock is needed before checking quiesced flag */
 183         if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
 184                 return;
 185
 186         hctx->run++;
 187
 188         /*
 189          * If we have previous entries on our dispatch list, grab them first for
 190          * more fair dispatch.
 191          */
 192         if (!list_empty_careful(&hctx->dispatch)) {
 193                 spin_lock(&hctx->lock);
 194                 if (!list_empty(&hctx->dispatch))
 195                         list_splice_init(&hctx->dispatch, &rq_list);
 196                 spin_unlock(&hctx->lock);
 197         }
 198
 199         /*
 200          * Only ask the scheduler for requests, if we didn't have residual
 201          * requests from the dispatch list. This is to avoid the case where
 202          * we only ever dispatch a fraction of the requests available because
 203          * of low device queue depth. Once we pull requests out of the IO
 204          * scheduler, we can no longer merge or sort them. So it's best to
 205          * leave them there for as long as we can. Mark the hw queue as
 206          * needing a restart in that case.
 207          *
 208          * We want to dispatch from the scheduler if there was nothing
 209          * on the dispatch list or we were able to dispatch from the
 210          * dispatch list.
 211          */
 212         if (!list_empty(&rq_list)) {
 213                 blk_mq_sched_mark_restart_hctx(hctx);
 214                 if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
 215                         if (has_sched_dispatch)
 216                                 blk_mq_do_dispatch_sched(hctx);
 217                         else
 218                                 blk_mq_do_dispatch_ctx(hctx);
 219                 }
 220         } else if (has_sched_dispatch) {
 221                 blk_mq_do_dispatch_sched(hctx);
 222         } else if (q->mq_ops->get_budget) {
 223                 /*
 224                  * If we need to get budget before queuing request, we
 225                  * dequeue request one by one from sw queue for avoiding
 226                  * to mess up I/O merge when dispatch runs out of resource.
 227                  *
 228                  * TODO: get more budgets, and dequeue more requests in
 229                  * one time.
 230                  */
 231                 blk_mq_do_dispatch_ctx(hctx);
 232         } else {
 233                 blk_mq_flush_busy_ctxs(hctx, &rq_list);
 234                 blk_mq_dispatch_rq_list(q, &rq_list, false);
 235         }
 236 }
 237
 238 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
 239                             struct request **merged_request)
 240 {
 241         struct request *rq;
 242
 243         switch (elv_merge(q, &rq, bio)) {
 244         case ELEVATOR_BACK_MERGE:
 245                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 246                         return false;
 247                 if (!bio_attempt_back_merge(q, rq, bio))
 248                         return false;
 249                 *merged_request = attempt_back_merge(q, rq);
 250                 if (!*merged_request)
 251                         elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
 252                 return true;
 253         case ELEVATOR_FRONT_MERGE:
 254                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 255                         return false;
 256                 if (!bio_attempt_front_merge(q, rq, bio))
 257                         return false;
 258                 *merged_request = attempt_front_merge(q, rq);
 259                 if (!*merged_request)
 260                         elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
 261                 return true;
 262         case ELEVATOR_DISCARD_MERGE:
 263                 return bio_attempt_discard_merge(q, rq, bio);
 264         default:
 265                 return false;
 266         }
 267 }
 268 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
 269
 270 /*
 271  * Reverse check our software queue for entries that we could potentially
 272  * merge with. Currently includes a hand-wavy stop count of 8, to not spend
 273  * too much time checking for merges.
 274  */
 275 static bool blk_mq_attempt_merge(struct request_queue *q,
 276                                  struct blk_mq_ctx *ctx, struct bio *bio)
 277 {
 278         struct request *rq;
 279         int checked = 8;
 280
 281         lockdep_assert_held(&ctx->lock);
 282
 283         list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
 284                 bool merged = false;
 285
 286                 if (!checked--)
 287                         break;
 288
 289                 if (!blk_rq_merge_ok(rq, bio))
 290                         continue;
 291
 292                 switch (blk_try_merge(rq, bio)) {
 293                 case ELEVATOR_BACK_MERGE:
 294                         if (blk_mq_sched_allow_merge(q, rq, bio))
 295                                 merged = bio_attempt_back_merge(q, rq, bio);
 296                         break;
 297                 case ELEVATOR_FRONT_MERGE:
 298                         if (blk_mq_sched_allow_merge(q, rq, bio))
 299                                 merged = bio_attempt_front_merge(q, rq, bio);
 300                         break;
 301                 case ELEVATOR_DISCARD_MERGE:
 302                         merged = bio_attempt_discard_merge(q, rq, bio);
 303                         break;
 304                 default:
 305                         continue;
 306                 }
 307
 308                 if (merged)
 309                         ctx->rq_merged++;
 310                 return merged;
 311         }
 312
 313         return false;
 314 }
 315
 316 bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
 317 {
 318         struct elevator_queue *e = q->elevator;
 319         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
 320         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 321         bool ret = false;
 322
 323         if (e && e->type->ops.mq.bio_merge) {
 324                 blk_mq_put_ctx(ctx);
 325                 return e->type->ops.mq.bio_merge(hctx, bio);
 326         }
 327
 328         if (hctx->flags & BLK_MQ_F_SHOULD_MERGE) {
 329                 /* default per sw-queue merge */
 330                 spin_lock(&ctx->lock);
 331                 ret = blk_mq_attempt_merge(q, ctx, bio);
 332                 spin_unlock(&ctx->lock);
 333         }
 334
 335         blk_mq_put_ctx(ctx);
 336         return ret;
 337 }
 338
 339 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
 340 {
 341         return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
 342 }
 343 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
 344
 345 void blk_mq_sched_request_inserted(struct request *rq)
 346 {
 347         trace_block_rq_insert(rq->q, rq);
 348 }
 349 EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
 350
 351 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
 352                                        bool has_sched,
 353                                        struct request *rq)
 354 {
 355         /* dispatch flush rq directly */
 356         if (rq->rq_flags & RQF_FLUSH_SEQ) {
 357                 spin_lock(&hctx->lock);
 358                 list_add(&rq->queuelist, &hctx->dispatch);
 359                 spin_unlock(&hctx->lock);
 360                 return true;
 361         }
 362
 363         if (has_sched)
 364                 rq->rq_flags |= RQF_SORTED;
 365
 366         return false;
 367 }
 368
 369 /**
 370  * list_for_each_entry_rcu_rr - iterate in a round-robin fashion over rcu list
 371  * @pos:    loop cursor.
 372  * @skip:   the list element that will not be examined. Iteration starts at
 373  *          @skip->next.
 374  * @head:   head of the list to examine. This list must have at least one
 375  *          element, namely @skip.
 376  * @member: name of the list_head structure within typeof(*pos).
 377  */
 378 #define list_for_each_entry_rcu_rr(pos, skip, head, member)             \
 379         for ((pos) = (skip);                                            \
 380              (pos = (pos)->member.next != (head) ? list_entry_rcu(      \
 381                         (pos)->member.next, typeof(*pos), member) :     \
 382               list_entry_rcu((pos)->member.next->next, typeof(*pos), member)), \
 383              (pos) != (skip); )
 384
 385 /*
 386  * Called after a driver tag has been freed to check whether a hctx needs to
 387  * be restarted. Restarts @hctx if its tag set is not shared. Restarts hardware
 388  * queues in a round-robin fashion if the tag set of @hctx is shared with other
 389  * hardware queues.
 390  */
 391 void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
 392 {
 393         struct blk_mq_tags *const tags = hctx->tags;
 394         struct blk_mq_tag_set *const set = hctx->queue->tag_set;
 395         struct request_queue *const queue = hctx->queue, *q;
 396         struct blk_mq_hw_ctx *hctx2;
 397         unsigned int i, j;
 398
 399         if (set->flags & BLK_MQ_F_TAG_SHARED) {
 400                 /*
 401                  * If this is 0, then we know that no hardware queues
 402                  * have RESTART marked. We're done.
 403                  */
 404                 if (!atomic_read(&queue->shared_hctx_restart))
 405                         return;
 406
 407                 rcu_read_lock();
 408                 list_for_each_entry_rcu_rr(q, queue, &set->tag_list,
 409                                            tag_set_list) {
 410                         queue_for_each_hw_ctx(q, hctx2, i)
 411                                 if (hctx2->tags == tags &&
 412                                     blk_mq_sched_restart_hctx(hctx2))
 413                                         goto done;
 414                 }
 415                 j = hctx->queue_num + 1;
 416                 for (i = 0; i < queue->nr_hw_queues; i++, j++) {
 417                         if (j == queue->nr_hw_queues)
 418                                 j = 0;
 419                         hctx2 = queue->queue_hw_ctx[j];
 420                         if (hctx2->tags == tags &&
 421                             blk_mq_sched_restart_hctx(hctx2))
 422                                 break;
 423                 }
 424 done:
 425                 rcu_read_unlock();
 426         } else {
 427                 blk_mq_sched_restart_hctx(hctx);
 428         }
 429 }
 430
 431 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
 432                                  bool run_queue, bool async)
 433 {
 434         struct request_queue *q = rq->q;
 435         struct elevator_queue *e = q->elevator;
 436         struct blk_mq_ctx *ctx = rq->mq_ctx;
 437         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 438
 439         /* flush rq in flush machinery need to be dispatched directly */
 440         if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
 441                 blk_insert_flush(rq);
 442                 goto run;
 443         }
 444
 445         WARN_ON(e && (rq->tag != -1));
 446
 447         if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
 448                 goto run;
 449
 450         if (e && e->type->ops.mq.insert_requests) {
 451                 LIST_HEAD(list);
 452
 453                 list_add(&rq->queuelist, &list);
 454                 e->type->ops.mq.insert_requests(hctx, &list, at_head);
 455         } else {
 456                 spin_lock(&ctx->lock);
 457                 __blk_mq_insert_request(hctx, rq, at_head);
 458                 spin_unlock(&ctx->lock);
 459         }
 460
 461 run:
 462         if (run_queue)
 463                 blk_mq_run_hw_queue(hctx, async);
 464 }
 465
 466 void blk_mq_sched_insert_requests(struct request_queue *q,
 467                                   struct blk_mq_ctx *ctx,
 468                                   struct list_head *list, bool run_queue_async)
 469 {
 470         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 471         struct elevator_queue *e = hctx->queue->elevator;
 472
 473         if (e && e->type->ops.mq.insert_requests)
 474                 e->type->ops.mq.insert_requests(hctx, list, false);
 475         else
 476                 blk_mq_insert_requests(hctx, ctx, list);
 477
 478         blk_mq_run_hw_queue(hctx, run_queue_async);
 479 }
 480
 481 static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
 482                                    struct blk_mq_hw_ctx *hctx,
 483                                    unsigned int hctx_idx)
 484 {
 485         if (hctx->sched_tags) {
 486                 blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
 487                 blk_mq_free_rq_map(hctx->sched_tags);
 488                 hctx->sched_tags = NULL;
 489         }
 490 }
 491
 492 static int blk_mq_sched_alloc_tags(struct request_queue *q,
 493                                    struct blk_mq_hw_ctx *hctx,
 494                                    unsigned int hctx_idx)
 495 {
 496         struct blk_mq_tag_set *set = q->tag_set;
 497         int ret;
 498
 499         hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
 500                                                set->reserved_tags);
 501         if (!hctx->sched_tags)
 502                 return -ENOMEM;
 503
 504         ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
 505         if (ret)
 506                 blk_mq_sched_free_tags(set, hctx, hctx_idx);
 507
 508         return ret;
 509 }
 510
 511 static void blk_mq_sched_tags_teardown(struct request_queue *q)
 512 {
 513         struct blk_mq_tag_set *set = q->tag_set;
 514         struct blk_mq_hw_ctx *hctx;
 515         int i;
 516
 517         queue_for_each_hw_ctx(q, hctx, i)
 518                 blk_mq_sched_free_tags(set, hctx, i);
 519 }
 520
 521 int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
 522                            unsigned int hctx_idx)
 523 {
 524         struct elevator_queue *e = q->elevator;
 525         int ret;
 526
 527         if (!e)
 528                 return 0;
 529
 530         ret = blk_mq_sched_alloc_tags(q, hctx, hctx_idx);
 531         if (ret)
 532                 return ret;
 533
 534         if (e->type->ops.mq.init_hctx) {
 535                 ret = e->type->ops.mq.init_hctx(hctx, hctx_idx);
 536                 if (ret) {
 537                         blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
 538                         return ret;
 539                 }
 540         }
 541
 542         blk_mq_debugfs_register_sched_hctx(q, hctx);
 543
 544         return 0;
 545 }
 546
 547 void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
 548                             unsigned int hctx_idx)
 549 {
 550         struct elevator_queue *e = q->elevator;
 551
 552         if (!e)
 553                 return;
 554
 555         blk_mq_debugfs_unregister_sched_hctx(hctx);
 556
 557         if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
 558                 e->type->ops.mq.exit_hctx(hctx, hctx_idx);
 559                 hctx->sched_data = NULL;
 560         }
 561
 562         blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
 563 }
 564
 565 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 566 {
 567         struct blk_mq_hw_ctx *hctx;
 568         struct elevator_queue *eq;
 569         unsigned int i;
 570         int ret;
 571
 572         if (!e) {
 573                 q->elevator = NULL;
 574                 return 0;
 575         }
 576
 577         /*
 578          * Default to double of smaller one between hw queue_depth and 128,
 579          * since we don't split into sync/async like the old code did.
 580          * Additionally, this is a per-hw queue depth.
 581          */
 582         q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
 583                                    BLKDEV_MAX_RQ);
 584
 585         queue_for_each_hw_ctx(q, hctx, i) {
 586                 ret = blk_mq_sched_alloc_tags(q, hctx, i);
 587                 if (ret)
 588                         goto err;
 589         }
 590
 591         ret = e->ops.mq.init_sched(q, e);
 592         if (ret)
 593                 goto err;
 594
 595         blk_mq_debugfs_register_sched(q);
 596
 597         queue_for_each_hw_ctx(q, hctx, i) {
 598                 if (e->ops.mq.init_hctx) {
 599                         ret = e->ops.mq.init_hctx(hctx, i);
 600                         if (ret) {
 601                                 eq = q->elevator;
 602                                 blk_mq_exit_sched(q, eq);
 603                                 kobject_put(&eq->kobj);
 604                                 return ret;
 605                         }
 606                 }
 607                 blk_mq_debugfs_register_sched_hctx(q, hctx);
 608         }
 609
 610         return 0;
 611
 612 err:
 613         blk_mq_sched_tags_teardown(q);
 614         q->elevator = NULL;
 615         return ret;
 616 }
 617
 618 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 619 {
 620         struct blk_mq_hw_ctx *hctx;
 621         unsigned int i;
 622
 623         queue_for_each_hw_ctx(q, hctx, i) {
 624                 blk_mq_debugfs_unregister_sched_hctx(hctx);
 625                 if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
 626                         e->type->ops.mq.exit_hctx(hctx, i);
 627                         hctx->sched_data = NULL;
 628                 }
 629         }
 630         blk_mq_debugfs_unregister_sched(q);
 631         if (e->type->ops.mq.exit_sched)
 632                 e->type->ops.mq.exit_sched(e);
 633         blk_mq_sched_tags_teardown(q);
 634         q->elevator = NULL;
 635 }
 636
 637 int blk_mq_sched_init(struct request_queue *q)
 638 {
 639         int ret;
 640
 641         mutex_lock(&q->sysfs_lock);
 642         ret = elevator_init(q, NULL);
 643         mutex_unlock(&q->sysfs_lock);
 644
 645         return ret;
 646 }