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)
  35 {
  36         struct request_queue *q = rq->q;
  37         struct io_context *ioc;
  38         struct io_cq *icq;
  39
  40         /*
  41          * May not have an IO context if it's a passthrough request
  42          */
  43         ioc = current->io_context;
  44         if (!ioc)
  45                 return;
  46
  47         spin_lock_irq(&q->queue_lock);
  48         icq = ioc_lookup_icq(ioc, q);
  49         spin_unlock_irq(&q->queue_lock);
  50
  51         if (!icq) {
  52                 icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
  53                 if (!icq)
  54                         return;
  55         }
  56         get_io_context(icq->ioc);
  57         rq->elv.icq = icq;
  58 }
  59
  60 /*
  61  * Mark a hardware queue as needing a restart. For shared queues, maintain
  62  * a count of how many hardware queues are marked for restart.
  63  */
  64 void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
  65 {
  66         if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  67                 return;
  68
  69         set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  70 }
  71 EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
  72
  73 void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
  74 {
  75         if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  76                 return;
  77         clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  78
  79         blk_mq_run_hw_queue(hctx, true);
  80 }
  81
  82 /*
  83  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
  84  * its queue by itself in its completion handler, so we don't need to
  85  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
  86  */
  87 static void 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         LIST_HEAD(rq_list);
  92
  93         do {
  94                 struct request *rq;
  95
  96                 if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
  97                         break;
  98
  99                 if (!blk_mq_get_dispatch_budget(hctx))
 100                         break;
 101
 102                 rq = e->type->ops.dispatch_request(hctx);
 103                 if (!rq) {
 104                         blk_mq_put_dispatch_budget(hctx);
 105                         break;
 106                 }
 107
 108                 /*
 109                  * Now this rq owns the budget which has to be released
 110                  * if this rq won't be queued to driver via .queue_rq()
 111                  * in blk_mq_dispatch_rq_list().
 112                  */
 113                 list_add(&rq->queuelist, &rq_list);
 114         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 115 }
 116
 117 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
 118                                           struct blk_mq_ctx *ctx)
 119 {
 120         unsigned short idx = ctx->index_hw[hctx->type];
 121
 122         if (++idx == hctx->nr_ctx)
 123                 idx = 0;
 124
 125         return hctx->ctxs[idx];
 126 }
 127
 128 /*
 129  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 130  * its queue by itself in its completion handler, so we don't need to
 131  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
 132  */
 133 static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 134 {
 135         struct request_queue *q = hctx->queue;
 136         LIST_HEAD(rq_list);
 137         struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
 138
 139         do {
 140                 struct request *rq;
 141
 142                 if (!sbitmap_any_bit_set(&hctx->ctx_map))
 143                         break;
 144
 145                 if (!blk_mq_get_dispatch_budget(hctx))
 146                         break;
 147
 148                 rq = blk_mq_dequeue_from_ctx(hctx, ctx);
 149                 if (!rq) {
 150                         blk_mq_put_dispatch_budget(hctx);
 151                         break;
 152                 }
 153
 154                 /*
 155                  * Now this rq owns the budget which has to be released
 156                  * if this rq won't be queued to driver via .queue_rq()
 157                  * in blk_mq_dispatch_rq_list().
 158                  */
 159                 list_add(&rq->queuelist, &rq_list);
 160
 161                 /* round robin for fair dispatch */
 162                 ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
 163
 164         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 165
 166         WRITE_ONCE(hctx->dispatch_from, ctx);
 167 }
 168
 169 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 170 {
 171         struct request_queue *q = hctx->queue;
 172         struct elevator_queue *e = q->elevator;
 173         const bool has_sched_dispatch = e && e->type->ops.dispatch_request;
 174         LIST_HEAD(rq_list);
 175
 176         /* RCU or SRCU read lock is needed before checking quiesced flag */
 177         if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
 178                 return;
 179
 180         hctx->run++;
 181
 182         /*
 183          * If we have previous entries on our dispatch list, grab them first for
 184          * more fair dispatch.
 185          */
 186         if (!list_empty_careful(&hctx->dispatch)) {
 187                 spin_lock(&hctx->lock);
 188                 if (!list_empty(&hctx->dispatch))
 189                         list_splice_init(&hctx->dispatch, &rq_list);
 190                 spin_unlock(&hctx->lock);
 191         }
 192
 193         /*
 194          * Only ask the scheduler for requests, if we didn't have residual
 195          * requests from the dispatch list. This is to avoid the case where
 196          * we only ever dispatch a fraction of the requests available because
 197          * of low device queue depth. Once we pull requests out of the IO
 198          * scheduler, we can no longer merge or sort them. So it's best to
 199          * leave them there for as long as we can. Mark the hw queue as
 200          * needing a restart in that case.
 201          *
 202          * We want to dispatch from the scheduler if there was nothing
 203          * on the dispatch list or we were able to dispatch from the
 204          * dispatch list.
 205          */
 206         if (!list_empty(&rq_list)) {
 207                 blk_mq_sched_mark_restart_hctx(hctx);
 208                 if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
 209                         if (has_sched_dispatch)
 210                                 blk_mq_do_dispatch_sched(hctx);
 211                         else
 212                                 blk_mq_do_dispatch_ctx(hctx);
 213                 }
 214         } else if (has_sched_dispatch) {
 215                 blk_mq_do_dispatch_sched(hctx);
 216         } else if (hctx->dispatch_busy) {
 217                 /* dequeue request one by one from sw queue if queue is busy */
 218                 blk_mq_do_dispatch_ctx(hctx);
 219         } else {
 220                 blk_mq_flush_busy_ctxs(hctx, &rq_list);
 221                 blk_mq_dispatch_rq_list(q, &rq_list, false);
 222         }
 223 }
 224
 225 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
 226                             struct request **merged_request)
 227 {
 228         struct request *rq;
 229
 230         switch (elv_merge(q, &rq, bio)) {
 231         case ELEVATOR_BACK_MERGE:
 232                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 233                         return false;
 234                 if (!bio_attempt_back_merge(q, rq, bio))
 235                         return false;
 236                 *merged_request = attempt_back_merge(q, rq);
 237                 if (!*merged_request)
 238                         elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
 239                 return true;
 240         case ELEVATOR_FRONT_MERGE:
 241                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 242                         return false;
 243                 if (!bio_attempt_front_merge(q, rq, bio))
 244                         return false;
 245                 *merged_request = attempt_front_merge(q, rq);
 246                 if (!*merged_request)
 247                         elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
 248                 return true;
 249         case ELEVATOR_DISCARD_MERGE:
 250                 return bio_attempt_discard_merge(q, rq, bio);
 251         default:
 252                 return false;
 253         }
 254 }
 255 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
 256
 257 /*
 258  * Iterate list of requests and see if we can merge this bio with any
 259  * of them.
 260  */
 261 bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
 262                            struct bio *bio)
 263 {
 264         struct request *rq;
 265         int checked = 8;
 266
 267         list_for_each_entry_reverse(rq, list, queuelist) {
 268                 bool merged = false;
 269
 270                 if (!checked--)
 271                         break;
 272
 273                 if (!blk_rq_merge_ok(rq, bio))
 274                         continue;
 275
 276                 switch (blk_try_merge(rq, bio)) {
 277                 case ELEVATOR_BACK_MERGE:
 278                         if (blk_mq_sched_allow_merge(q, rq, bio))
 279                                 merged = bio_attempt_back_merge(q, rq, bio);
 280                         break;
 281                 case ELEVATOR_FRONT_MERGE:
 282                         if (blk_mq_sched_allow_merge(q, rq, bio))
 283                                 merged = bio_attempt_front_merge(q, rq, bio);
 284                         break;
 285                 case ELEVATOR_DISCARD_MERGE:
 286                         merged = bio_attempt_discard_merge(q, rq, bio);
 287                         break;
 288                 default:
 289                         continue;
 290                 }
 291
 292                 return merged;
 293         }
 294
 295         return false;
 296 }
 297 EXPORT_SYMBOL_GPL(blk_mq_bio_list_merge);
 298
 299 /*
 300  * Reverse check our software queue for entries that we could potentially
 301  * merge with. Currently includes a hand-wavy stop count of 8, to not spend
 302  * too much time checking for merges.
 303  */
 304 static bool blk_mq_attempt_merge(struct request_queue *q,
 305                                  struct blk_mq_ctx *ctx, struct bio *bio)
 306 {
 307         lockdep_assert_held(&ctx->lock);
 308
 309         if (blk_mq_bio_list_merge(q, &ctx->rq_list, bio)) {
 310                 ctx->rq_merged++;
 311                 return true;
 312         }
 313
 314         return false;
 315 }
 316
 317 bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
 318 {
 319         struct elevator_queue *e = q->elevator;
 320         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
 321         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx->cpu);
 322         bool ret = false;
 323
 324         if (e && e->type->ops.bio_merge) {
 325                 blk_mq_put_ctx(ctx);
 326                 return e->type->ops.bio_merge(hctx, bio);
 327         }
 328
 329         if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
 330                         !list_empty_careful(&ctx->rq_list)) {
 331                 /* default per sw-queue merge */
 332                 spin_lock(&ctx->lock);
 333                 ret = blk_mq_attempt_merge(q, ctx, bio);
 334                 spin_unlock(&ctx->lock);
 335         }
 336
 337         blk_mq_put_ctx(ctx);
 338         return ret;
 339 }
 340
 341 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
 342 {
 343         return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
 344 }
 345 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
 346
 347 void blk_mq_sched_request_inserted(struct request *rq)
 348 {
 349         trace_block_rq_insert(rq->q, rq);
 350 }
 351 EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
 352
 353 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
 354                                        bool has_sched,
 355                                        struct request *rq)
 356 {
 357         /* dispatch flush rq directly */
 358         if (rq->rq_flags & RQF_FLUSH_SEQ) {
 359                 spin_lock(&hctx->lock);
 360                 list_add(&rq->queuelist, &hctx->dispatch);
 361                 spin_unlock(&hctx->lock);
 362                 return true;
 363         }
 364
 365         if (has_sched)
 366                 rq->rq_flags |= RQF_SORTED;
 367
 368         return false;
 369 }
 370
 371 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
 372                                  bool run_queue, bool async)
 373 {
 374         struct request_queue *q = rq->q;
 375         struct elevator_queue *e = q->elevator;
 376         struct blk_mq_ctx *ctx = rq->mq_ctx;
 377         struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 378
 379         /* flush rq in flush machinery need to be dispatched directly */
 380         if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
 381                 blk_insert_flush(rq);
 382                 goto run;
 383         }
 384
 385         WARN_ON(e && (rq->tag != -1));
 386
 387         if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
 388                 goto run;
 389
 390         if (e && e->type->ops.insert_requests) {
 391                 LIST_HEAD(list);
 392
 393                 list_add(&rq->queuelist, &list);
 394                 e->type->ops.insert_requests(hctx, &list, at_head);
 395         } else {
 396                 spin_lock(&ctx->lock);
 397                 __blk_mq_insert_request(hctx, rq, at_head);
 398                 spin_unlock(&ctx->lock);
 399         }
 400
 401 run:
 402         if (run_queue)
 403                 blk_mq_run_hw_queue(hctx, async);
 404 }
 405
 406 void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
 407                                   struct blk_mq_ctx *ctx,
 408                                   struct list_head *list, bool run_queue_async)
 409 {
 410         struct elevator_queue *e;
 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                 else
 424                         blk_mq_insert_requests(hctx, ctx, list);
 425         }
 426
 427         blk_mq_run_hw_queue(hctx, run_queue_async);
 428 }
 429
 430 static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
 431                                    struct blk_mq_hw_ctx *hctx,
 432                                    unsigned int hctx_idx)
 433 {
 434         if (hctx->sched_tags) {
 435                 blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
 436                 blk_mq_free_rq_map(hctx->sched_tags);
 437                 hctx->sched_tags = NULL;
 438         }
 439 }
 440
 441 static int blk_mq_sched_alloc_tags(struct request_queue *q,
 442                                    struct blk_mq_hw_ctx *hctx,
 443                                    unsigned int hctx_idx)
 444 {
 445         struct blk_mq_tag_set *set = q->tag_set;
 446         int ret;
 447
 448         hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
 449                                                set->reserved_tags);
 450         if (!hctx->sched_tags)
 451                 return -ENOMEM;
 452
 453         ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
 454         if (ret)
 455                 blk_mq_sched_free_tags(set, hctx, hctx_idx);
 456
 457         return ret;
 458 }
 459
 460 static void blk_mq_sched_tags_teardown(struct request_queue *q)
 461 {
 462         struct blk_mq_tag_set *set = q->tag_set;
 463         struct blk_mq_hw_ctx *hctx;
 464         int i;
 465
 466         queue_for_each_hw_ctx(q, hctx, i)
 467                 blk_mq_sched_free_tags(set, hctx, i);
 468 }
 469
 470 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 471 {
 472         struct blk_mq_hw_ctx *hctx;
 473         struct elevator_queue *eq;
 474         unsigned int i;
 475         int ret;
 476
 477         if (!e) {
 478                 q->elevator = NULL;
 479                 q->nr_requests = q->tag_set->queue_depth;
 480                 return 0;
 481         }
 482
 483         /*
 484          * Default to double of smaller one between hw queue_depth and 128,
 485          * since we don't split into sync/async like the old code did.
 486          * Additionally, this is a per-hw queue depth.
 487          */
 488         q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
 489                                    BLKDEV_MAX_RQ);
 490
 491         queue_for_each_hw_ctx(q, hctx, i) {
 492                 ret = blk_mq_sched_alloc_tags(q, hctx, i);
 493                 if (ret)
 494                         goto err;
 495         }
 496
 497         ret = e->ops.init_sched(q, e);
 498         if (ret)
 499                 goto err;
 500
 501         blk_mq_debugfs_register_sched(q);
 502
 503         queue_for_each_hw_ctx(q, hctx, i) {
 504                 if (e->ops.init_hctx) {
 505                         ret = e->ops.init_hctx(hctx, i);
 506                         if (ret) {
 507                                 eq = q->elevator;
 508                                 blk_mq_exit_sched(q, eq);
 509                                 kobject_put(&eq->kobj);
 510                                 return ret;
 511                         }
 512                 }
 513                 blk_mq_debugfs_register_sched_hctx(q, hctx);
 514         }
 515
 516         return 0;
 517
 518 err:
 519         blk_mq_sched_tags_teardown(q);
 520         q->elevator = NULL;
 521         return ret;
 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 int i;
 528
 529         queue_for_each_hw_ctx(q, hctx, i) {
 530                 blk_mq_debugfs_unregister_sched_hctx(hctx);
 531                 if (e->type->ops.exit_hctx && hctx->sched_data) {
 532                         e->type->ops.exit_hctx(hctx, i);
 533                         hctx->sched_data = NULL;
 534                 }
 535         }
 536         blk_mq_debugfs_unregister_sched(q);
 537         if (e->type->ops.exit_sched)
 538                 e->type->ops.exit_sched(e);
 539         blk_mq_sched_tags_teardown(q);
 540         q->elevator = NULL;
 541 }