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  * Iterate list of requests and see if we can merge this bio with any
 272  * of them.
 273  */
 274 bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
 275                            struct bio *bio)
 276 {
 277         struct request *rq;
 278         int checked = 8;
 279
 280         list_for_each_entry_reverse(rq, list, queuelist) {
 281                 bool merged = false;
 282
 283                 if (!checked--)
 284                         break;
 285
 286                 if (!blk_rq_merge_ok(rq, bio))
 287                         continue;
 288
 289                 switch (blk_try_merge(rq, bio)) {
 290                 case ELEVATOR_BACK_MERGE:
 291                         if (blk_mq_sched_allow_merge(q, rq, bio))
 292                                 merged = bio_attempt_back_merge(q, rq, bio);
 293                         break;
 294                 case ELEVATOR_FRONT_MERGE:
 295                         if (blk_mq_sched_allow_merge(q, rq, bio))
 296                                 merged = bio_attempt_front_merge(q, rq, bio);
 297                         break;
 298                 case ELEVATOR_DISCARD_MERGE:
 299                         merged = bio_attempt_discard_merge(q, rq, bio);
 300                         break;
 301                 default:
 302                         continue;
 303                 }
 304
 305                 return merged;
 306         }
 307
 308         return false;
 309 }
 310 EXPORT_SYMBOL_GPL(blk_mq_bio_list_merge);
 311
 312 /*
 313  * Reverse check our software queue for entries that we could potentially
 314  * merge with. Currently includes a hand-wavy stop count of 8, to not spend
 315  * too much time checking for merges.
 316  */
 317 static bool blk_mq_attempt_merge(struct request_queue *q,
 318                                  struct blk_mq_ctx *ctx, struct bio *bio)
 319 {
 320         lockdep_assert_held(&ctx->lock);
 321
 322         if (blk_mq_bio_list_merge(q, &ctx->rq_list, bio)) {
 323                 ctx->rq_merged++;
 324                 return true;
 325         }
 326
 327         return false;
 328 }
 329
 330 bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
 331 {
 332         struct elevator_queue *e = q->elevator;
 333         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
 334         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 335         bool ret = false;
 336
 337         if (e && e->type->ops.mq.bio_merge) {
 338                 blk_mq_put_ctx(ctx);
 339                 return e->type->ops.mq.bio_merge(hctx, bio);
 340         }
 341
 342         if (hctx->flags & BLK_MQ_F_SHOULD_MERGE) {
 343                 /* default per sw-queue merge */
 344                 spin_lock(&ctx->lock);
 345                 ret = blk_mq_attempt_merge(q, ctx, bio);
 346                 spin_unlock(&ctx->lock);
 347         }
 348
 349         blk_mq_put_ctx(ctx);
 350         return ret;
 351 }
 352
 353 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
 354 {
 355         return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
 356 }
 357 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
 358
 359 void blk_mq_sched_request_inserted(struct request *rq)
 360 {
 361         trace_block_rq_insert(rq->q, rq);
 362 }
 363 EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
 364
 365 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
 366                                        bool has_sched,
 367                                        struct request *rq)
 368 {
 369         /* dispatch flush rq directly */
 370         if (rq->rq_flags & RQF_FLUSH_SEQ) {
 371                 spin_lock(&hctx->lock);
 372                 list_add(&rq->queuelist, &hctx->dispatch);
 373                 spin_unlock(&hctx->lock);
 374                 return true;
 375         }
 376
 377         if (has_sched)
 378                 rq->rq_flags |= RQF_SORTED;
 379
 380         return false;
 381 }
 382
 383 /**
 384  * list_for_each_entry_rcu_rr - iterate in a round-robin fashion over rcu list
 385  * @pos:    loop cursor.
 386  * @skip:   the list element that will not be examined. Iteration starts at
 387  *          @skip->next.
 388  * @head:   head of the list to examine. This list must have at least one
 389  *          element, namely @skip.
 390  * @member: name of the list_head structure within typeof(*pos).
 391  */
 392 #define list_for_each_entry_rcu_rr(pos, skip, head, member)             \
 393         for ((pos) = (skip);                                            \
 394              (pos = (pos)->member.next != (head) ? list_entry_rcu(      \
 395                         (pos)->member.next, typeof(*pos), member) :     \
 396               list_entry_rcu((pos)->member.next->next, typeof(*pos), member)), \
 397              (pos) != (skip); )
 398
 399 /*
 400  * Called after a driver tag has been freed to check whether a hctx needs to
 401  * be restarted. Restarts @hctx if its tag set is not shared. Restarts hardware
 402  * queues in a round-robin fashion if the tag set of @hctx is shared with other
 403  * hardware queues.
 404  */
 405 void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
 406 {
 407         struct blk_mq_tags *const tags = hctx->tags;
 408         struct blk_mq_tag_set *const set = hctx->queue->tag_set;
 409         struct request_queue *const queue = hctx->queue, *q;
 410         struct blk_mq_hw_ctx *hctx2;
 411         unsigned int i, j;
 412
 413         if (set->flags & BLK_MQ_F_TAG_SHARED) {
 414                 /*
 415                  * If this is 0, then we know that no hardware queues
 416                  * have RESTART marked. We're done.
 417                  */
 418                 if (!atomic_read(&queue->shared_hctx_restart))
 419                         return;
 420
 421                 rcu_read_lock();
 422                 list_for_each_entry_rcu_rr(q, queue, &set->tag_list,
 423                                            tag_set_list) {
 424                         queue_for_each_hw_ctx(q, hctx2, i)
 425                                 if (hctx2->tags == tags &&
 426                                     blk_mq_sched_restart_hctx(hctx2))
 427                                         goto done;
 428                 }
 429                 j = hctx->queue_num + 1;
 430                 for (i = 0; i < queue->nr_hw_queues; i++, j++) {
 431                         if (j == queue->nr_hw_queues)
 432                                 j = 0;
 433                         hctx2 = queue->queue_hw_ctx[j];
 434                         if (hctx2->tags == tags &&
 435                             blk_mq_sched_restart_hctx(hctx2))
 436                                 break;
 437                 }
 438 done:
 439                 rcu_read_unlock();
 440         } else {
 441                 blk_mq_sched_restart_hctx(hctx);
 442         }
 443 }
 444
 445 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
 446                                  bool run_queue, bool async)
 447 {
 448         struct request_queue *q = rq->q;
 449         struct elevator_queue *e = q->elevator;
 450         struct blk_mq_ctx *ctx = rq->mq_ctx;
 451         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 452
 453         /* flush rq in flush machinery need to be dispatched directly */
 454         if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
 455                 blk_insert_flush(rq);
 456                 goto run;
 457         }
 458
 459         WARN_ON(e && (rq->tag != -1));
 460
 461         if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
 462                 goto run;
 463
 464         if (e && e->type->ops.mq.insert_requests) {
 465                 LIST_HEAD(list);
 466
 467                 list_add(&rq->queuelist, &list);
 468                 e->type->ops.mq.insert_requests(hctx, &list, at_head);
 469         } else {
 470                 spin_lock(&ctx->lock);
 471                 __blk_mq_insert_request(hctx, rq, at_head);
 472                 spin_unlock(&ctx->lock);
 473         }
 474
 475 run:
 476         if (run_queue)
 477                 blk_mq_run_hw_queue(hctx, async);
 478 }
 479
 480 void blk_mq_sched_insert_requests(struct request_queue *q,
 481                                   struct blk_mq_ctx *ctx,
 482                                   struct list_head *list, bool run_queue_async)
 483 {
 484         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 485         struct elevator_queue *e = hctx->queue->elevator;
 486
 487         if (e && e->type->ops.mq.insert_requests)
 488                 e->type->ops.mq.insert_requests(hctx, list, false);
 489         else
 490                 blk_mq_insert_requests(hctx, ctx, list);
 491
 492         blk_mq_run_hw_queue(hctx, run_queue_async);
 493 }
 494
 495 static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
 496                                    struct blk_mq_hw_ctx *hctx,
 497                                    unsigned int hctx_idx)
 498 {
 499         if (hctx->sched_tags) {
 500                 blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
 501                 blk_mq_free_rq_map(hctx->sched_tags);
 502                 hctx->sched_tags = NULL;
 503         }
 504 }
 505
 506 static int blk_mq_sched_alloc_tags(struct request_queue *q,
 507                                    struct blk_mq_hw_ctx *hctx,
 508                                    unsigned int hctx_idx)
 509 {
 510         struct blk_mq_tag_set *set = q->tag_set;
 511         int ret;
 512
 513         hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
 514                                                set->reserved_tags);
 515         if (!hctx->sched_tags)
 516                 return -ENOMEM;
 517
 518         ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
 519         if (ret)
 520                 blk_mq_sched_free_tags(set, hctx, hctx_idx);
 521
 522         return ret;
 523 }
 524
 525 static void blk_mq_sched_tags_teardown(struct request_queue *q)
 526 {
 527         struct blk_mq_tag_set *set = q->tag_set;
 528         struct blk_mq_hw_ctx *hctx;
 529         int i;
 530
 531         queue_for_each_hw_ctx(q, hctx, i)
 532                 blk_mq_sched_free_tags(set, hctx, i);
 533 }
 534
 535 int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
 536                            unsigned int hctx_idx)
 537 {
 538         struct elevator_queue *e = q->elevator;
 539         int ret;
 540
 541         if (!e)
 542                 return 0;
 543
 544         ret = blk_mq_sched_alloc_tags(q, hctx, hctx_idx);
 545         if (ret)
 546                 return ret;
 547
 548         if (e->type->ops.mq.init_hctx) {
 549                 ret = e->type->ops.mq.init_hctx(hctx, hctx_idx);
 550                 if (ret) {
 551                         blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
 552                         return ret;
 553                 }
 554         }
 555
 556         blk_mq_debugfs_register_sched_hctx(q, hctx);
 557
 558         return 0;
 559 }
 560
 561 void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
 562                             unsigned int hctx_idx)
 563 {
 564         struct elevator_queue *e = q->elevator;
 565
 566         if (!e)
 567                 return;
 568
 569         blk_mq_debugfs_unregister_sched_hctx(hctx);
 570
 571         if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
 572                 e->type->ops.mq.exit_hctx(hctx, hctx_idx);
 573                 hctx->sched_data = NULL;
 574         }
 575
 576         blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
 577 }
 578
 579 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 580 {
 581         struct blk_mq_hw_ctx *hctx;
 582         struct elevator_queue *eq;
 583         unsigned int i;
 584         int ret;
 585
 586         if (!e) {
 587                 q->elevator = NULL;
 588                 q->nr_requests = q->tag_set->queue_depth;
 589                 return 0;
 590         }
 591
 592         /*
 593          * Default to double of smaller one between hw queue_depth and 128,
 594          * since we don't split into sync/async like the old code did.
 595          * Additionally, this is a per-hw queue depth.
 596          */
 597         q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
 598                                    BLKDEV_MAX_RQ);
 599
 600         queue_for_each_hw_ctx(q, hctx, i) {
 601                 ret = blk_mq_sched_alloc_tags(q, hctx, i);
 602                 if (ret)
 603                         goto err;
 604         }
 605
 606         ret = e->ops.mq.init_sched(q, e);
 607         if (ret)
 608                 goto err;
 609
 610         blk_mq_debugfs_register_sched(q);
 611
 612         queue_for_each_hw_ctx(q, hctx, i) {
 613                 if (e->ops.mq.init_hctx) {
 614                         ret = e->ops.mq.init_hctx(hctx, i);
 615                         if (ret) {
 616                                 eq = q->elevator;
 617                                 blk_mq_exit_sched(q, eq);
 618                                 kobject_put(&eq->kobj);
 619                                 return ret;
 620                         }
 621                 }
 622                 blk_mq_debugfs_register_sched_hctx(q, hctx);
 623         }
 624
 625         return 0;
 626
 627 err:
 628         blk_mq_sched_tags_teardown(q);
 629         q->elevator = NULL;
 630         return ret;
 631 }
 632
 633 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 634 {
 635         struct blk_mq_hw_ctx *hctx;
 636         unsigned int i;
 637
 638         queue_for_each_hw_ctx(q, hctx, i) {
 639                 blk_mq_debugfs_unregister_sched_hctx(hctx);
 640                 if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
 641                         e->type->ops.mq.exit_hctx(hctx, i);
 642                         hctx->sched_data = NULL;
 643                 }
 644         }
 645         blk_mq_debugfs_unregister_sched(q);
 646         if (e->type->ops.mq.exit_sched)
 647                 e->type->ops.mq.exit_sched(e);
 648         blk_mq_sched_tags_teardown(q);
 649         q->elevator = NULL;
 650 }