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.has_work && !e->type->ops.has_work(hctx))
  89                         break;
  90
  91                 if (!blk_mq_get_dispatch_budget(hctx))
  92                         break;
  93
  94                 rq = e->type->ops.dispatch_request(hctx);
  95                 if (!rq) {
  96                         blk_mq_put_dispatch_budget(hctx);
  97                         break;
  98                 }
  99
 100                 /*
 101                  * Now this rq owns the budget which has to be released
 102                  * if this rq won't be queued to driver via .queue_rq()
 103                  * in blk_mq_dispatch_rq_list().
 104                  */
 105                 list_add(&rq->queuelist, &rq_list);
 106         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 107 }
 108
 109 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
 110                                           struct blk_mq_ctx *ctx)
 111 {
 112         unsigned short idx = ctx->index_hw[hctx->type];
 113
 114         if (++idx == hctx->nr_ctx)
 115                 idx = 0;
 116
 117         return hctx->ctxs[idx];
 118 }
 119
 120 /*
 121  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 122  * its queue by itself in its completion handler, so we don't need to
 123  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
 124  */
 125 static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 126 {
 127         struct request_queue *q = hctx->queue;
 128         LIST_HEAD(rq_list);
 129         struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
 130
 131         do {
 132                 struct request *rq;
 133
 134                 if (!sbitmap_any_bit_set(&hctx->ctx_map))
 135                         break;
 136
 137                 if (!blk_mq_get_dispatch_budget(hctx))
 138                         break;
 139
 140                 rq = blk_mq_dequeue_from_ctx(hctx, ctx);
 141                 if (!rq) {
 142                         blk_mq_put_dispatch_budget(hctx);
 143                         break;
 144                 }
 145
 146                 /*
 147                  * Now this rq owns the budget which has to be released
 148                  * if this rq won't be queued to driver via .queue_rq()
 149                  * in blk_mq_dispatch_rq_list().
 150                  */
 151                 list_add(&rq->queuelist, &rq_list);
 152
 153                 /* round robin for fair dispatch */
 154                 ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
 155
 156         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 157
 158         WRITE_ONCE(hctx->dispatch_from, ctx);
 159 }
 160
 161 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 162 {
 163         struct request_queue *q = hctx->queue;
 164         struct elevator_queue *e = q->elevator;
 165         const bool has_sched_dispatch = e && e->type->ops.dispatch_request;
 166         LIST_HEAD(rq_list);
 167
 168         /* RCU or SRCU read lock is needed before checking quiesced flag */
 169         if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
 170                 return;
 171
 172         hctx->run++;
 173
 174         /*
 175          * If we have previous entries on our dispatch list, grab them first for
 176          * more fair dispatch.
 177          */
 178         if (!list_empty_careful(&hctx->dispatch)) {
 179                 spin_lock(&hctx->lock);
 180                 if (!list_empty(&hctx->dispatch))
 181                         list_splice_init(&hctx->dispatch, &rq_list);
 182                 spin_unlock(&hctx->lock);
 183         }
 184
 185         /*
 186          * Only ask the scheduler for requests, if we didn't have residual
 187          * requests from the dispatch list. This is to avoid the case where
 188          * we only ever dispatch a fraction of the requests available because
 189          * of low device queue depth. Once we pull requests out of the IO
 190          * scheduler, we can no longer merge or sort them. So it's best to
 191          * leave them there for as long as we can. Mark the hw queue as
 192          * needing a restart in that case.
 193          *
 194          * We want to dispatch from the scheduler if there was nothing
 195          * on the dispatch list or we were able to dispatch from the
 196          * dispatch list.
 197          */
 198         if (!list_empty(&rq_list)) {
 199                 blk_mq_sched_mark_restart_hctx(hctx);
 200                 if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
 201                         if (has_sched_dispatch)
 202                                 blk_mq_do_dispatch_sched(hctx);
 203                         else
 204                                 blk_mq_do_dispatch_ctx(hctx);
 205                 }
 206         } else if (has_sched_dispatch) {
 207                 blk_mq_do_dispatch_sched(hctx);
 208         } else if (hctx->dispatch_busy) {
 209                 /* dequeue request one by one from sw queue if queue is busy */
 210                 blk_mq_do_dispatch_ctx(hctx);
 211         } else {
 212                 blk_mq_flush_busy_ctxs(hctx, &rq_list);
 213                 blk_mq_dispatch_rq_list(q, &rq_list, false);
 214         }
 215 }
 216
 217 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
 218                             struct request **merged_request)
 219 {
 220         struct request *rq;
 221
 222         switch (elv_merge(q, &rq, bio)) {
 223         case ELEVATOR_BACK_MERGE:
 224                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 225                         return false;
 226                 if (!bio_attempt_back_merge(q, rq, bio))
 227                         return false;
 228                 *merged_request = attempt_back_merge(q, rq);
 229                 if (!*merged_request)
 230                         elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
 231                 return true;
 232         case ELEVATOR_FRONT_MERGE:
 233                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 234                         return false;
 235                 if (!bio_attempt_front_merge(q, rq, bio))
 236                         return false;
 237                 *merged_request = attempt_front_merge(q, rq);
 238                 if (!*merged_request)
 239                         elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
 240                 return true;
 241         case ELEVATOR_DISCARD_MERGE:
 242                 return bio_attempt_discard_merge(q, rq, bio);
 243         default:
 244                 return false;
 245         }
 246 }
 247 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
 248
 249 /*
 250  * Iterate list of requests and see if we can merge this bio with any
 251  * of them.
 252  */
 253 bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
 254                            struct bio *bio)
 255 {
 256         struct request *rq;
 257         int checked = 8;
 258
 259         list_for_each_entry_reverse(rq, list, queuelist) {
 260                 bool merged = false;
 261
 262                 if (!checked--)
 263                         break;
 264
 265                 if (!blk_rq_merge_ok(rq, bio))
 266                         continue;
 267
 268                 switch (blk_try_merge(rq, bio)) {
 269                 case ELEVATOR_BACK_MERGE:
 270                         if (blk_mq_sched_allow_merge(q, rq, bio))
 271                                 merged = bio_attempt_back_merge(q, rq, bio);
 272                         break;
 273                 case ELEVATOR_FRONT_MERGE:
 274                         if (blk_mq_sched_allow_merge(q, rq, bio))
 275                                 merged = bio_attempt_front_merge(q, rq, bio);
 276                         break;
 277                 case ELEVATOR_DISCARD_MERGE:
 278                         merged = bio_attempt_discard_merge(q, rq, bio);
 279                         break;
 280                 default:
 281                         continue;
 282                 }
 283
 284                 return merged;
 285         }
 286
 287         return false;
 288 }
 289 EXPORT_SYMBOL_GPL(blk_mq_bio_list_merge);
 290
 291 /*
 292  * Reverse check our software queue for entries that we could potentially
 293  * merge with. Currently includes a hand-wavy stop count of 8, to not spend
 294  * too much time checking for merges.
 295  */
 296 static bool blk_mq_attempt_merge(struct request_queue *q,
 297                                  struct blk_mq_ctx *ctx, struct bio *bio)
 298 {
 299         lockdep_assert_held(&ctx->lock);
 300
 301         if (blk_mq_bio_list_merge(q, &ctx->rq_list, bio)) {
 302                 ctx->rq_merged++;
 303                 return true;
 304         }
 305
 306         return false;
 307 }
 308
 309 bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
 310 {
 311         struct elevator_queue *e = q->elevator;
 312         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
 313         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx->cpu);
 314         bool ret = false;
 315
 316         if (e && e->type->ops.bio_merge) {
 317                 blk_mq_put_ctx(ctx);
 318                 return e->type->ops.bio_merge(hctx, bio);
 319         }
 320
 321         if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
 322                         !list_empty_careful(&ctx->rq_list)) {
 323                 /* default per sw-queue merge */
 324                 spin_lock(&ctx->lock);
 325                 ret = blk_mq_attempt_merge(q, ctx, bio);
 326                 spin_unlock(&ctx->lock);
 327         }
 328
 329         blk_mq_put_ctx(ctx);
 330         return ret;
 331 }
 332
 333 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
 334 {
 335         return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
 336 }
 337 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
 338
 339 void blk_mq_sched_request_inserted(struct request *rq)
 340 {
 341         trace_block_rq_insert(rq->q, rq);
 342 }
 343 EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
 344
 345 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
 346                                        bool has_sched,
 347                                        struct request *rq)
 348 {
 349         /* dispatch flush rq directly */
 350         if (rq->rq_flags & RQF_FLUSH_SEQ) {
 351                 spin_lock(&hctx->lock);
 352                 list_add(&rq->queuelist, &hctx->dispatch);
 353                 spin_unlock(&hctx->lock);
 354                 return true;
 355         }
 356
 357         if (has_sched)
 358                 rq->rq_flags |= RQF_SORTED;
 359
 360         return false;
 361 }
 362
 363 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
 364                                  bool run_queue, bool async)
 365 {
 366         struct request_queue *q = rq->q;
 367         struct elevator_queue *e = q->elevator;
 368         struct blk_mq_ctx *ctx = rq->mq_ctx;
 369         struct blk_mq_hw_ctx *hctx;
 370
 371         hctx = blk_mq_map_queue(q, rq->cmd_flags, ctx->cpu);
 372
 373         /* flush rq in flush machinery need to be dispatched directly */
 374         if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
 375                 blk_insert_flush(rq);
 376                 goto run;
 377         }
 378
 379         WARN_ON(e && (rq->tag != -1));
 380
 381         if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
 382                 goto run;
 383
 384         if (e && e->type->ops.insert_requests) {
 385                 LIST_HEAD(list);
 386
 387                 list_add(&rq->queuelist, &list);
 388                 e->type->ops.insert_requests(hctx, &list, at_head);
 389         } else {
 390                 spin_lock(&ctx->lock);
 391                 __blk_mq_insert_request(hctx, rq, at_head);
 392                 spin_unlock(&ctx->lock);
 393         }
 394
 395 run:
 396         if (run_queue)
 397                 blk_mq_run_hw_queue(hctx, async);
 398 }
 399
 400 void blk_mq_sched_insert_requests(struct request_queue *q,
 401                                   struct blk_mq_ctx *ctx,
 402                                   struct list_head *list, bool run_queue_async)
 403 {
 404         struct blk_mq_hw_ctx *hctx;
 405         struct elevator_queue *e;
 406         struct request *rq;
 407
 408         /* For list inserts, requests better be on the same hw queue */
 409         rq = list_first_entry(list, struct request, queuelist);
 410         hctx = blk_mq_map_queue(q, rq->cmd_flags, ctx->cpu);
 411
 412         e = hctx->queue->elevator;
 413         if (e && e->type->ops.insert_requests)
 414                 e->type->ops.insert_requests(hctx, list, false);
 415         else {
 416                 /*
 417                  * try to issue requests directly if the hw queue isn't
 418                  * busy in case of 'none' scheduler, and this way may save
 419                  * us one extra enqueue & dequeue to sw queue.
 420                  */
 421                 if (!hctx->dispatch_busy && !e && !run_queue_async) {
 422                         blk_mq_try_issue_list_directly(hctx, list);
 423                         if (list_empty(list))
 424                                 return;
 425                 }
 426                 blk_mq_insert_requests(hctx, ctx, list);
 427         }
 428
 429         blk_mq_run_hw_queue(hctx, run_queue_async);
 430 }
 431
 432 static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
 433                                    struct blk_mq_hw_ctx *hctx,
 434                                    unsigned int hctx_idx)
 435 {
 436         if (hctx->sched_tags) {
 437                 blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
 438                 blk_mq_free_rq_map(hctx->sched_tags);
 439                 hctx->sched_tags = NULL;
 440         }
 441 }
 442
 443 static int blk_mq_sched_alloc_tags(struct request_queue *q,
 444                                    struct blk_mq_hw_ctx *hctx,
 445                                    unsigned int hctx_idx)
 446 {
 447         struct blk_mq_tag_set *set = q->tag_set;
 448         int ret;
 449
 450         hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
 451                                                set->reserved_tags);
 452         if (!hctx->sched_tags)
 453                 return -ENOMEM;
 454
 455         ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
 456         if (ret)
 457                 blk_mq_sched_free_tags(set, hctx, hctx_idx);
 458
 459         return ret;
 460 }
 461
 462 static void blk_mq_sched_tags_teardown(struct request_queue *q)
 463 {
 464         struct blk_mq_tag_set *set = q->tag_set;
 465         struct blk_mq_hw_ctx *hctx;
 466         int i;
 467
 468         queue_for_each_hw_ctx(q, hctx, i)
 469                 blk_mq_sched_free_tags(set, hctx, i);
 470 }
 471
 472 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 473 {
 474         struct blk_mq_hw_ctx *hctx;
 475         struct elevator_queue *eq;
 476         unsigned int i;
 477         int ret;
 478
 479         if (!e) {
 480                 q->elevator = NULL;
 481                 q->nr_requests = q->tag_set->queue_depth;
 482                 return 0;
 483         }
 484
 485         /*
 486          * Default to double of smaller one between hw queue_depth and 128,
 487          * since we don't split into sync/async like the old code did.
 488          * Additionally, this is a per-hw queue depth.
 489          */
 490         q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
 491                                    BLKDEV_MAX_RQ);
 492
 493         queue_for_each_hw_ctx(q, hctx, i) {
 494                 ret = blk_mq_sched_alloc_tags(q, hctx, i);
 495                 if (ret)
 496                         goto err;
 497         }
 498
 499         ret = e->ops.init_sched(q, e);
 500         if (ret)
 501                 goto err;
 502
 503         blk_mq_debugfs_register_sched(q);
 504
 505         queue_for_each_hw_ctx(q, hctx, i) {
 506                 if (e->ops.init_hctx) {
 507                         ret = e->ops.init_hctx(hctx, i);
 508                         if (ret) {
 509                                 eq = q->elevator;
 510                                 blk_mq_exit_sched(q, eq);
 511                                 kobject_put(&eq->kobj);
 512                                 return ret;
 513                         }
 514                 }
 515                 blk_mq_debugfs_register_sched_hctx(q, hctx);
 516         }
 517
 518         return 0;
 519
 520 err:
 521         blk_mq_sched_tags_teardown(q);
 522         q->elevator = NULL;
 523         return ret;
 524 }
 525
 526 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 527 {
 528         struct blk_mq_hw_ctx *hctx;
 529         unsigned int i;
 530
 531         queue_for_each_hw_ctx(q, hctx, i) {
 532                 blk_mq_debugfs_unregister_sched_hctx(hctx);
 533                 if (e->type->ops.exit_hctx && hctx->sched_data) {
 534                         e->type->ops.exit_hctx(hctx, i);
 535                         hctx->sched_data = NULL;
 536                 }
 537         }
 538         blk_mq_debugfs_unregister_sched(q);
 539         if (e->type->ops.exit_sched)
 540                 e->type->ops.exit_sched(e);
 541         blk_mq_sched_tags_teardown(q);
 542         q->elevator = NULL;
 543 }