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         set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  63 }
  64
  65 void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
  66 {
  67         if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  68                 return;
  69         clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  70
  71         blk_mq_run_hw_queue(hctx, true);
  72 }
  73
  74 /*
  75  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
  76  * its queue by itself in its completion handler, so we don't need to
  77  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
  78  */
  79 static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
  80 {
  81         struct request_queue *q = hctx->queue;
  82         struct elevator_queue *e = q->elevator;
  83         LIST_HEAD(rq_list);
  84
  85         do {
  86                 struct request *rq;
  87
  88                 if (e->type->ops.mq.has_work &&
  89                                 !e->type->ops.mq.has_work(hctx))
  90                         break;
  91
  92                 if (!blk_mq_get_dispatch_budget(hctx))
  93                         break;
  94
  95                 rq = e->type->ops.mq.dispatch_request(hctx);
  96                 if (!rq) {
  97                         blk_mq_put_dispatch_budget(hctx);
  98                         break;
  99                 }
 100
 101                 /*
 102                  * Now this rq owns the budget which has to be released
 103                  * if this rq won't be queued to driver via .queue_rq()
 104                  * in blk_mq_dispatch_rq_list().
 105                  */
 106                 list_add(&rq->queuelist, &rq_list);
 107         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 108 }
 109
 110 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
 111                                           struct blk_mq_ctx *ctx)
 112 {
 113         unsigned idx = ctx->index_hw;
 114
 115         if (++idx == hctx->nr_ctx)
 116                 idx = 0;
 117
 118         return hctx->ctxs[idx];
 119 }
 120
 121 /*
 122  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 123  * its queue by itself in its completion handler, so we don't need to
 124  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
 125  */
 126 static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 127 {
 128         struct request_queue *q = hctx->queue;
 129         LIST_HEAD(rq_list);
 130         struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
 131
 132         do {
 133                 struct request *rq;
 134
 135                 if (!sbitmap_any_bit_set(&hctx->ctx_map))
 136                         break;
 137
 138                 if (!blk_mq_get_dispatch_budget(hctx))
 139                         break;
 140
 141                 rq = blk_mq_dequeue_from_ctx(hctx, ctx);
 142                 if (!rq) {
 143                         blk_mq_put_dispatch_budget(hctx);
 144                         break;
 145                 }
 146
 147                 /*
 148                  * Now this rq owns the budget which has to be released
 149                  * if this rq won't be queued to driver via .queue_rq()
 150                  * in blk_mq_dispatch_rq_list().
 151                  */
 152                 list_add(&rq->queuelist, &rq_list);
 153
 154                 /* round robin for fair dispatch */
 155                 ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
 156
 157         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 158
 159         WRITE_ONCE(hctx->dispatch_from, ctx);
 160 }
 161
 162 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 163 {
 164         struct request_queue *q = hctx->queue;
 165         struct elevator_queue *e = q->elevator;
 166         const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
 167         LIST_HEAD(rq_list);
 168
 169         /* RCU or SRCU read lock is needed before checking quiesced flag */
 170         if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
 171                 return;
 172
 173         hctx->run++;
 174
 175         /*
 176          * If we have previous entries on our dispatch list, grab them first for
 177          * more fair dispatch.
 178          */
 179         if (!list_empty_careful(&hctx->dispatch)) {
 180                 spin_lock(&hctx->lock);
 181                 if (!list_empty(&hctx->dispatch))
 182                         list_splice_init(&hctx->dispatch, &rq_list);
 183                 spin_unlock(&hctx->lock);
 184         }
 185
 186         /*
 187          * Only ask the scheduler for requests, if we didn't have residual
 188          * requests from the dispatch list. This is to avoid the case where
 189          * we only ever dispatch a fraction of the requests available because
 190          * of low device queue depth. Once we pull requests out of the IO
 191          * scheduler, we can no longer merge or sort them. So it's best to
 192          * leave them there for as long as we can. Mark the hw queue as
 193          * needing a restart in that case.
 194          *
 195          * We want to dispatch from the scheduler if there was nothing
 196          * on the dispatch list or we were able to dispatch from the
 197          * dispatch list.
 198          */
 199         if (!list_empty(&rq_list)) {
 200                 blk_mq_sched_mark_restart_hctx(hctx);
 201                 if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
 202                         if (has_sched_dispatch)
 203                                 blk_mq_do_dispatch_sched(hctx);
 204                         else
 205                                 blk_mq_do_dispatch_ctx(hctx);
 206                 }
 207         } else if (has_sched_dispatch) {
 208                 blk_mq_do_dispatch_sched(hctx);
 209         } else if (hctx->dispatch_busy) {
 210                 /* dequeue request one by one from sw queue if queue is busy */
 211                 blk_mq_do_dispatch_ctx(hctx);
 212         } else {
 213                 blk_mq_flush_busy_ctxs(hctx, &rq_list);
 214                 blk_mq_dispatch_rq_list(q, &rq_list, false);
 215         }
 216 }
 217
 218 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
 219                             struct request **merged_request)
 220 {
 221         struct request *rq;
 222
 223         switch (elv_merge(q, &rq, bio)) {
 224         case ELEVATOR_BACK_MERGE:
 225                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 226                         return false;
 227                 if (!bio_attempt_back_merge(q, rq, bio))
 228                         return false;
 229                 *merged_request = attempt_back_merge(q, rq);
 230                 if (!*merged_request)
 231                         elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
 232                 return true;
 233         case ELEVATOR_FRONT_MERGE:
 234                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 235                         return false;
 236                 if (!bio_attempt_front_merge(q, rq, bio))
 237                         return false;
 238                 *merged_request = attempt_front_merge(q, rq);
 239                 if (!*merged_request)
 240                         elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
 241                 return true;
 242         case ELEVATOR_DISCARD_MERGE:
 243                 return bio_attempt_discard_merge(q, rq, bio);
 244         default:
 245                 return false;
 246         }
 247 }
 248 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
 249
 250 /*
 251  * Iterate list of requests and see if we can merge this bio with any
 252  * of them.
 253  */
 254 bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
 255                            struct bio *bio)
 256 {
 257         struct request *rq;
 258         int checked = 8;
 259
 260         list_for_each_entry_reverse(rq, list, queuelist) {
 261                 bool merged = false;
 262
 263                 if (!checked--)
 264                         break;
 265
 266                 if (!blk_rq_merge_ok(rq, bio))
 267                         continue;
 268
 269                 switch (blk_try_merge(rq, bio)) {
 270                 case ELEVATOR_BACK_MERGE:
 271                         if (blk_mq_sched_allow_merge(q, rq, bio))
 272                                 merged = bio_attempt_back_merge(q, rq, bio);
 273                         break;
 274                 case ELEVATOR_FRONT_MERGE:
 275                         if (blk_mq_sched_allow_merge(q, rq, bio))
 276                                 merged = bio_attempt_front_merge(q, rq, bio);
 277                         break;
 278                 case ELEVATOR_DISCARD_MERGE:
 279                         merged = bio_attempt_discard_merge(q, rq, bio);
 280                         break;
 281                 default:
 282                         continue;
 283                 }
 284
 285                 return merged;
 286         }
 287
 288         return false;
 289 }
 290 EXPORT_SYMBOL_GPL(blk_mq_bio_list_merge);
 291
 292 /*
 293  * Reverse check our software queue for entries that we could potentially
 294  * merge with. Currently includes a hand-wavy stop count of 8, to not spend
 295  * too much time checking for merges.
 296  */
 297 static bool blk_mq_attempt_merge(struct request_queue *q,
 298                                  struct blk_mq_ctx *ctx, struct bio *bio)
 299 {
 300         lockdep_assert_held(&ctx->lock);
 301
 302         if (blk_mq_bio_list_merge(q, &ctx->rq_list, bio)) {
 303                 ctx->rq_merged++;
 304                 return true;
 305         }
 306
 307         return false;
 308 }
 309
 310 bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
 311 {
 312         struct elevator_queue *e = q->elevator;
 313         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
 314         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 315         bool ret = false;
 316
 317         if (e && e->type->ops.mq.bio_merge) {
 318                 blk_mq_put_ctx(ctx);
 319                 return e->type->ops.mq.bio_merge(hctx, bio);
 320         }
 321
 322         if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
 323                         !list_empty_careful(&ctx->rq_list)) {
 324                 /* default per sw-queue merge */
 325                 spin_lock(&ctx->lock);
 326                 ret = blk_mq_attempt_merge(q, ctx, bio);
 327                 spin_unlock(&ctx->lock);
 328         }
 329
 330         blk_mq_put_ctx(ctx);
 331         return ret;
 332 }
 333
 334 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
 335 {
 336         return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
 337 }
 338 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
 339
 340 void blk_mq_sched_request_inserted(struct request *rq)
 341 {
 342         trace_block_rq_insert(rq->q, rq);
 343 }
 344 EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
 345
 346 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
 347                                        bool has_sched,
 348                                        struct request *rq)
 349 {
 350         /* dispatch flush rq directly */
 351         if (rq->rq_flags & RQF_FLUSH_SEQ) {
 352                 spin_lock(&hctx->lock);
 353                 list_add(&rq->queuelist, &hctx->dispatch);
 354                 spin_unlock(&hctx->lock);
 355                 return true;
 356         }
 357
 358         if (has_sched)
 359                 rq->rq_flags |= RQF_SORTED;
 360
 361         return false;
 362 }
 363
 364 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
 365                                  bool run_queue, bool async)
 366 {
 367         struct request_queue *q = rq->q;
 368         struct elevator_queue *e = q->elevator;
 369         struct blk_mq_ctx *ctx = rq->mq_ctx;
 370         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 371
 372         /* flush rq in flush machinery need to be dispatched directly */
 373         if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
 374                 blk_insert_flush(rq);
 375                 goto run;
 376         }
 377
 378         WARN_ON(e && (rq->tag != -1));
 379
 380         if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
 381                 goto run;
 382
 383         if (e && e->type->ops.mq.insert_requests) {
 384                 LIST_HEAD(list);
 385
 386                 list_add(&rq->queuelist, &list);
 387                 e->type->ops.mq.insert_requests(hctx, &list, at_head);
 388         } else {
 389                 spin_lock(&ctx->lock);
 390                 __blk_mq_insert_request(hctx, rq, at_head);
 391                 spin_unlock(&ctx->lock);
 392         }
 393
 394 run:
 395         if (run_queue)
 396                 blk_mq_run_hw_queue(hctx, async);
 397 }
 398
 399 void blk_mq_sched_insert_requests(struct request_queue *q,
 400                                   struct blk_mq_ctx *ctx,
 401                                   struct list_head *list, bool run_queue_async)
 402 {
 403         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 404         struct elevator_queue *e = hctx->queue->elevator;
 405
 406         if (e && e->type->ops.mq.insert_requests)
 407                 e->type->ops.mq.insert_requests(hctx, list, false);
 408         else {
 409                 /*
 410                  * try to issue requests directly if the hw queue isn't
 411                  * busy in case of 'none' scheduler, and this way may save
 412                  * us one extra enqueue & dequeue to sw queue.
 413                  */
 414                 if (!hctx->dispatch_busy && !e && !run_queue_async) {
 415                         blk_mq_try_issue_list_directly(hctx, list);
 416                         if (list_empty(list))
 417                                 return;
 418                 }
 419                 blk_mq_insert_requests(hctx, ctx, list);
 420         }
 421
 422         blk_mq_run_hw_queue(hctx, run_queue_async);
 423 }
 424
 425 static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
 426                                    struct blk_mq_hw_ctx *hctx,
 427                                    unsigned int hctx_idx)
 428 {
 429         if (hctx->sched_tags) {
 430                 blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
 431                 blk_mq_free_rq_map(hctx->sched_tags);
 432                 hctx->sched_tags = NULL;
 433         }
 434 }
 435
 436 static int blk_mq_sched_alloc_tags(struct request_queue *q,
 437                                    struct blk_mq_hw_ctx *hctx,
 438                                    unsigned int hctx_idx)
 439 {
 440         struct blk_mq_tag_set *set = q->tag_set;
 441         int ret;
 442
 443         hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
 444                                                set->reserved_tags);
 445         if (!hctx->sched_tags)
 446                 return -ENOMEM;
 447
 448         ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
 449         if (ret)
 450                 blk_mq_sched_free_tags(set, hctx, hctx_idx);
 451
 452         return ret;
 453 }
 454
 455 static void blk_mq_sched_tags_teardown(struct request_queue *q)
 456 {
 457         struct blk_mq_tag_set *set = q->tag_set;
 458         struct blk_mq_hw_ctx *hctx;
 459         int i;
 460
 461         queue_for_each_hw_ctx(q, hctx, i)
 462                 blk_mq_sched_free_tags(set, hctx, i);
 463 }
 464
 465 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 466 {
 467         struct blk_mq_hw_ctx *hctx;
 468         struct elevator_queue *eq;
 469         unsigned int i;
 470         int ret;
 471
 472         if (!e) {
 473                 q->elevator = NULL;
 474                 q->nr_requests = q->tag_set->queue_depth;
 475                 return 0;
 476         }
 477
 478         /*
 479          * Default to double of smaller one between hw queue_depth and 128,
 480          * since we don't split into sync/async like the old code did.
 481          * Additionally, this is a per-hw queue depth.
 482          */
 483         q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
 484                                    BLKDEV_MAX_RQ);
 485
 486         queue_for_each_hw_ctx(q, hctx, i) {
 487                 ret = blk_mq_sched_alloc_tags(q, hctx, i);
 488                 if (ret)
 489                         goto err;
 490         }
 491
 492         ret = e->ops.mq.init_sched(q, e);
 493         if (ret)
 494                 goto err;
 495
 496         blk_mq_debugfs_register_sched(q);
 497
 498         queue_for_each_hw_ctx(q, hctx, i) {
 499                 if (e->ops.mq.init_hctx) {
 500                         ret = e->ops.mq.init_hctx(hctx, i);
 501                         if (ret) {
 502                                 eq = q->elevator;
 503                                 blk_mq_exit_sched(q, eq);
 504                                 kobject_put(&eq->kobj);
 505                                 return ret;
 506                         }
 507                 }
 508                 blk_mq_debugfs_register_sched_hctx(q, hctx);
 509         }
 510
 511         return 0;
 512
 513 err:
 514         blk_mq_sched_tags_teardown(q);
 515         q->elevator = NULL;
 516         return ret;
 517 }
 518
 519 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 520 {
 521         struct blk_mq_hw_ctx *hctx;
 522         unsigned int i;
 523
 524         queue_for_each_hw_ctx(q, hctx, i) {
 525                 blk_mq_debugfs_unregister_sched_hctx(hctx);
 526                 if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
 527                         e->type->ops.mq.exit_hctx(hctx, i);
 528                         hctx->sched_data = NULL;
 529                 }
 530         }
 531         blk_mq_debugfs_unregister_sched(q);
 532         if (e->type->ops.mq.exit_sched)
 533                 e->type->ops.mq.exit_sched(e);
 534         blk_mq_sched_tags_teardown(q);
 535         q->elevator = NULL;
 536 }