block/kyber-iosched.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * The Kyber I/O scheduler. Controls latency by throttling queue depths using
   4  * scalable techniques.
   5  *
   6  * Copyright (C) 2017 Facebook
   7  */
   8
   9 #include <linux/kernel.h>
  10 #include <linux/blkdev.h>
  11 #include <linux/blk-mq.h>
  12 #include <linux/elevator.h>
  13 #include <linux/module.h>
  14 #include <linux/sbitmap.h>
  15
  16 #include <trace/events/block.h>
  17
  18 #include "blk.h"
  19 #include "blk-mq.h"
  20 #include "blk-mq-debugfs.h"
  21 #include "blk-mq-sched.h"
  22 #include "blk-mq-tag.h"
  23
  24 #define CREATE_TRACE_POINTS
  25 #include <trace/events/kyber.h>
  26
  27 /*
  28  * Scheduling domains: the device is divided into multiple domains based on the
  29  * request type.
  30  */
  31 enum {
  32         KYBER_READ,
  33         KYBER_WRITE,
  34         KYBER_DISCARD,
  35         KYBER_OTHER,
  36         KYBER_NUM_DOMAINS,
  37 };
  38
  39 static const char *kyber_domain_names[] = {
  40         [KYBER_READ] = "READ",
  41         [KYBER_WRITE] = "WRITE",
  42         [KYBER_DISCARD] = "DISCARD",
  43         [KYBER_OTHER] = "OTHER",
  44 };
  45
  46 enum {
  47         /*
  48          * In order to prevent starvation of synchronous requests by a flood of
  49          * asynchronous requests, we reserve 25% of requests for synchronous
  50          * operations.
  51          */
  52         KYBER_ASYNC_PERCENT = 75,
  53 };
  54
  55 /*
  56  * Maximum device-wide depth for each scheduling domain.
  57  *
  58  * Even for fast devices with lots of tags like NVMe, you can saturate the
  59  * device with only a fraction of the maximum possible queue depth. So, we cap
  60  * these to a reasonable value.
  61  */
  62 static const unsigned int kyber_depth[] = {
  63         [KYBER_READ] = 256,
  64         [KYBER_WRITE] = 128,
  65         [KYBER_DISCARD] = 64,
  66         [KYBER_OTHER] = 16,
  67 };
  68
  69 /*
  70  * Default latency targets for each scheduling domain.
  71  */
  72 static const u64 kyber_latency_targets[] = {
  73         [KYBER_READ] = 2ULL * NSEC_PER_MSEC,
  74         [KYBER_WRITE] = 10ULL * NSEC_PER_MSEC,
  75         [KYBER_DISCARD] = 5ULL * NSEC_PER_SEC,
  76 };
  77
  78 /*
  79  * Batch size (number of requests we'll dispatch in a row) for each scheduling
  80  * domain.
  81  */
  82 static const unsigned int kyber_batch_size[] = {
  83         [KYBER_READ] = 16,
  84         [KYBER_WRITE] = 8,
  85         [KYBER_DISCARD] = 1,
  86         [KYBER_OTHER] = 1,
  87 };
  88
  89 /*
  90  * Requests latencies are recorded in a histogram with buckets defined relative
  91  * to the target latency:
  92  *
  93  * <= 1/4 * target latency
  94  * <= 1/2 * target latency
  95  * <= 3/4 * target latency
  96  * <= target latency
  97  * <= 1 1/4 * target latency
  98  * <= 1 1/2 * target latency
  99  * <= 1 3/4 * target latency
 100  * > 1 3/4 * target latency
 101  */
 102 enum {
 103         /*
 104          * The width of the latency histogram buckets is
 105          * 1 / (1 << KYBER_LATENCY_SHIFT) * target latency.
 106          */
 107         KYBER_LATENCY_SHIFT = 2,
 108         /*
 109          * The first (1 << KYBER_LATENCY_SHIFT) buckets are <= target latency,
 110          * thus, "good".
 111          */
 112         KYBER_GOOD_BUCKETS = 1 << KYBER_LATENCY_SHIFT,
 113         /* There are also (1 << KYBER_LATENCY_SHIFT) "bad" buckets. */
 114         KYBER_LATENCY_BUCKETS = 2 << KYBER_LATENCY_SHIFT,
 115 };
 116
 117 /*
 118  * We measure both the total latency and the I/O latency (i.e., latency after
 119  * submitting to the device).
 120  */
 121 enum {
 122         KYBER_TOTAL_LATENCY,
 123         KYBER_IO_LATENCY,
 124 };
 125
 126 static const char *kyber_latency_type_names[] = {
 127         [KYBER_TOTAL_LATENCY] = "total",
 128         [KYBER_IO_LATENCY] = "I/O",
 129 };
 130
 131 /*
 132  * Per-cpu latency histograms: total latency and I/O latency for each scheduling
 133  * domain except for KYBER_OTHER.
 134  */
 135 struct kyber_cpu_latency {
 136         atomic_t buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
 137 };
 138
 139 /*
 140  * There is a same mapping between ctx & hctx and kcq & khd,
 141  * we use request->mq_ctx->index_hw to index the kcq in khd.
 142  */
 143 struct kyber_ctx_queue {
 144         /*
 145          * Used to ensure operations on rq_list and kcq_map to be an atmoic one.
 146          * Also protect the rqs on rq_list when merge.
 147          */
 148         spinlock_t lock;
 149         struct list_head rq_list[KYBER_NUM_DOMAINS];
 150 } ____cacheline_aligned_in_smp;
 151
 152 struct kyber_queue_data {
 153         struct request_queue *q;
 154         dev_t dev;
 155
 156         /*
 157          * Each scheduling domain has a limited number of in-flight requests
 158          * device-wide, limited by these tokens.
 159          */
 160         struct sbitmap_queue domain_tokens[KYBER_NUM_DOMAINS];
 161
 162         /*
 163          * Async request percentage, converted to per-word depth for
 164          * sbitmap_get_shallow().
 165          */
 166         unsigned int async_depth;
 167
 168         struct kyber_cpu_latency __percpu *cpu_latency;
 169
 170         /* Timer for stats aggregation and adjusting domain tokens. */
 171         struct timer_list timer;
 172
 173         unsigned int latency_buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
 174
 175         unsigned long latency_timeout[KYBER_OTHER];
 176
 177         int domain_p99[KYBER_OTHER];
 178
 179         /* Target latencies in nanoseconds. */
 180         u64 latency_targets[KYBER_OTHER];
 181 };
 182
 183 struct kyber_hctx_data {
 184         spinlock_t lock;
 185         struct list_head rqs[KYBER_NUM_DOMAINS];
 186         unsigned int cur_domain;
 187         unsigned int batching;
 188         struct kyber_ctx_queue *kcqs;
 189         struct sbitmap kcq_map[KYBER_NUM_DOMAINS];
 190         struct sbq_wait domain_wait[KYBER_NUM_DOMAINS];
 191         struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
 192         atomic_t wait_index[KYBER_NUM_DOMAINS];
 193 };
 194
 195 static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
 196                              void *key);
 197
 198 static unsigned int kyber_sched_domain(unsigned int op)
 199 {
 200         switch (op & REQ_OP_MASK) {
 201         case REQ_OP_READ:
 202                 return KYBER_READ;
 203         case REQ_OP_WRITE:
 204                 return KYBER_WRITE;
 205         case REQ_OP_DISCARD:
 206                 return KYBER_DISCARD;
 207         default:
 208                 return KYBER_OTHER;
 209         }
 210 }
 211
 212 static void flush_latency_buckets(struct kyber_queue_data *kqd,
 213                                   struct kyber_cpu_latency *cpu_latency,
 214                                   unsigned int sched_domain, unsigned int type)
 215 {
 216         unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
 217         atomic_t *cpu_buckets = cpu_latency->buckets[sched_domain][type];
 218         unsigned int bucket;
 219
 220         for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
 221                 buckets[bucket] += atomic_xchg(&cpu_buckets[bucket], 0);
 222 }
 223
 224 /*
 225  * Calculate the histogram bucket with the given percentile rank, or -1 if there
 226  * aren't enough samples yet.
 227  */
 228 static int calculate_percentile(struct kyber_queue_data *kqd,
 229                                 unsigned int sched_domain, unsigned int type,
 230                                 unsigned int percentile)
 231 {
 232         unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
 233         unsigned int bucket, samples = 0, percentile_samples;
 234
 235         for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
 236                 samples += buckets[bucket];
 237
 238         if (!samples)
 239                 return -1;
 240
 241         /*
 242          * We do the calculation once we have 500 samples or one second passes
 243          * since the first sample was recorded, whichever comes first.
 244          */
 245         if (!kqd->latency_timeout[sched_domain])
 246                 kqd->latency_timeout[sched_domain] = max(jiffies + HZ, 1UL);
 247         if (samples < 500 &&
 248             time_is_after_jiffies(kqd->latency_timeout[sched_domain])) {
 249                 return -1;
 250         }
 251         kqd->latency_timeout[sched_domain] = 0;
 252
 253         percentile_samples = DIV_ROUND_UP(samples * percentile, 100);
 254         for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS - 1; bucket++) {
 255                 if (buckets[bucket] >= percentile_samples)
 256                         break;
 257                 percentile_samples -= buckets[bucket];
 258         }
 259         memset(buckets, 0, sizeof(kqd->latency_buckets[sched_domain][type]));
 260
 261         trace_kyber_latency(kqd->dev, kyber_domain_names[sched_domain],
 262                             kyber_latency_type_names[type], percentile,
 263                             bucket + 1, 1 << KYBER_LATENCY_SHIFT, samples);
 264
 265         return bucket;
 266 }
 267
 268 static void kyber_resize_domain(struct kyber_queue_data *kqd,
 269                                 unsigned int sched_domain, unsigned int depth)
 270 {
 271         depth = clamp(depth, 1U, kyber_depth[sched_domain]);
 272         if (depth != kqd->domain_tokens[sched_domain].sb.depth) {
 273                 sbitmap_queue_resize(&kqd->domain_tokens[sched_domain], depth);
 274                 trace_kyber_adjust(kqd->dev, kyber_domain_names[sched_domain],
 275                                    depth);
 276         }
 277 }
 278
 279 static void kyber_timer_fn(struct timer_list *t)
 280 {
 281         struct kyber_queue_data *kqd = from_timer(kqd, t, timer);
 282         unsigned int sched_domain;
 283         int cpu;
 284         bool bad = false;
 285
 286         /* Sum all of the per-cpu latency histograms. */
 287         for_each_online_cpu(cpu) {
 288                 struct kyber_cpu_latency *cpu_latency;
 289
 290                 cpu_latency = per_cpu_ptr(kqd->cpu_latency, cpu);
 291                 for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
 292                         flush_latency_buckets(kqd, cpu_latency, sched_domain,
 293                                               KYBER_TOTAL_LATENCY);
 294                         flush_latency_buckets(kqd, cpu_latency, sched_domain,
 295                                               KYBER_IO_LATENCY);
 296                 }
 297         }
 298
 299         /*
 300          * Check if any domains have a high I/O latency, which might indicate
 301          * congestion in the device. Note that we use the p90; we don't want to
 302          * be too sensitive to outliers here.
 303          */
 304         for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
 305                 int p90;
 306
 307                 p90 = calculate_percentile(kqd, sched_domain, KYBER_IO_LATENCY,
 308                                            90);
 309                 if (p90 >= KYBER_GOOD_BUCKETS)
 310                         bad = true;
 311         }
 312
 313         /*
 314          * Adjust the scheduling domain depths. If we determined that there was
 315          * congestion, we throttle all domains with good latencies. Either way,
 316          * we ease up on throttling domains with bad latencies.
 317          */
 318         for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
 319                 unsigned int orig_depth, depth;
 320                 int p99;
 321
 322                 p99 = calculate_percentile(kqd, sched_domain,
 323                                            KYBER_TOTAL_LATENCY, 99);
 324                 /*
 325                  * This is kind of subtle: different domains will not
 326                  * necessarily have enough samples to calculate the latency
 327                  * percentiles during the same window, so we have to remember
 328                  * the p99 for the next time we observe congestion; once we do,
 329                  * we don't want to throttle again until we get more data, so we
 330                  * reset it to -1.
 331                  */
 332                 if (bad) {
 333                         if (p99 < 0)
 334                                 p99 = kqd->domain_p99[sched_domain];
 335                         kqd->domain_p99[sched_domain] = -1;
 336                 } else if (p99 >= 0) {
 337                         kqd->domain_p99[sched_domain] = p99;
 338                 }
 339                 if (p99 < 0)
 340                         continue;
 341
 342                 /*
 343                  * If this domain has bad latency, throttle less. Otherwise,
 344                  * throttle more iff we determined that there is congestion.
 345                  *
 346                  * The new depth is scaled linearly with the p99 latency vs the
 347                  * latency target. E.g., if the p99 is 3/4 of the target, then
 348                  * we throttle down to 3/4 of the current depth, and if the p99
 349                  * is 2x the target, then we double the depth.
 350                  */
 351                 if (bad || p99 >= KYBER_GOOD_BUCKETS) {
 352                         orig_depth = kqd->domain_tokens[sched_domain].sb.depth;
 353                         depth = (orig_depth * (p99 + 1)) >> KYBER_LATENCY_SHIFT;
 354                         kyber_resize_domain(kqd, sched_domain, depth);
 355                 }
 356         }
 357 }
 358
 359 static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
 360 {
 361         struct kyber_queue_data *kqd;
 362         int ret = -ENOMEM;
 363         int i;
 364
 365         kqd = kzalloc_node(sizeof(*kqd), GFP_KERNEL, q->node);
 366         if (!kqd)
 367                 goto err;
 368
 369         kqd->q = q;
 370         kqd->dev = disk_devt(q->disk);
 371
 372         kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency,
 373                                             GFP_KERNEL | __GFP_ZERO);
 374         if (!kqd->cpu_latency)
 375                 goto err_kqd;
 376
 377         timer_setup(&kqd->timer, kyber_timer_fn, 0);
 378
 379         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
 380                 WARN_ON(!kyber_depth[i]);
 381                 WARN_ON(!kyber_batch_size[i]);
 382                 ret = sbitmap_queue_init_node(&kqd->domain_tokens[i],
 383                                               kyber_depth[i], -1, false,
 384                                               GFP_KERNEL, q->node);
 385                 if (ret) {
 386                         while (--i >= 0)
 387                                 sbitmap_queue_free(&kqd->domain_tokens[i]);
 388                         goto err_buckets;
 389                 }
 390         }
 391
 392         for (i = 0; i < KYBER_OTHER; i++) {
 393                 kqd->domain_p99[i] = -1;
 394                 kqd->latency_targets[i] = kyber_latency_targets[i];
 395         }
 396
 397         return kqd;
 398
 399 err_buckets:
 400         free_percpu(kqd->cpu_latency);
 401 err_kqd:
 402         kfree(kqd);
 403 err:
 404         return ERR_PTR(ret);
 405 }
 406
 407 static int kyber_init_sched(struct request_queue *q, struct elevator_type *e)
 408 {
 409         struct kyber_queue_data *kqd;
 410         struct elevator_queue *eq;
 411
 412         eq = elevator_alloc(q, e);
 413         if (!eq)
 414                 return -ENOMEM;
 415
 416         kqd = kyber_queue_data_alloc(q);
 417         if (IS_ERR(kqd)) {
 418                 kobject_put(&eq->kobj);
 419                 return PTR_ERR(kqd);
 420         }
 421
 422         blk_stat_enable_accounting(q);
 423
 424         eq->elevator_data = kqd;
 425         q->elevator = eq;
 426
 427         return 0;
 428 }
 429
 430 static void kyber_exit_sched(struct elevator_queue *e)
 431 {
 432         struct kyber_queue_data *kqd = e->elevator_data;
 433         int i;
 434
 435         del_timer_sync(&kqd->timer);
 436
 437         for (i = 0; i < KYBER_NUM_DOMAINS; i++)
 438                 sbitmap_queue_free(&kqd->domain_tokens[i]);
 439         free_percpu(kqd->cpu_latency);
 440         kfree(kqd);
 441 }
 442
 443 static void kyber_ctx_queue_init(struct kyber_ctx_queue *kcq)
 444 {
 445         unsigned int i;
 446
 447         spin_lock_init(&kcq->lock);
 448         for (i = 0; i < KYBER_NUM_DOMAINS; i++)
 449                 INIT_LIST_HEAD(&kcq->rq_list[i]);
 450 }
 451
 452 static void kyber_depth_updated(struct blk_mq_hw_ctx *hctx)
 453 {
 454         struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
 455         struct blk_mq_tags *tags = hctx->sched_tags;
 456         unsigned int shift = tags->bitmap_tags->sb.shift;
 457
 458         kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;
 459
 460         sbitmap_queue_min_shallow_depth(tags->bitmap_tags, kqd->async_depth);
 461 }
 462
 463 static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
 464 {
 465         struct kyber_hctx_data *khd;
 466         int i;
 467
 468         khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
 469         if (!khd)
 470                 return -ENOMEM;
 471
 472         khd->kcqs = kmalloc_array_node(hctx->nr_ctx,
 473                                        sizeof(struct kyber_ctx_queue),
 474                                        GFP_KERNEL, hctx->numa_node);
 475         if (!khd->kcqs)
 476                 goto err_khd;
 477
 478         for (i = 0; i < hctx->nr_ctx; i++)
 479                 kyber_ctx_queue_init(&khd->kcqs[i]);
 480
 481         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
 482                 if (sbitmap_init_node(&khd->kcq_map[i], hctx->nr_ctx,
 483                                       ilog2(8), GFP_KERNEL, hctx->numa_node,
 484                                       false, false)) {
 485                         while (--i >= 0)
 486                                 sbitmap_free(&khd->kcq_map[i]);
 487                         goto err_kcqs;
 488                 }
 489         }
 490
 491         spin_lock_init(&khd->lock);
 492
 493         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
 494                 INIT_LIST_HEAD(&khd->rqs[i]);
 495                 khd->domain_wait[i].sbq = NULL;
 496                 init_waitqueue_func_entry(&khd->domain_wait[i].wait,
 497                                           kyber_domain_wake);
 498                 khd->domain_wait[i].wait.private = hctx;
 499                 INIT_LIST_HEAD(&khd->domain_wait[i].wait.entry);
 500                 atomic_set(&khd->wait_index[i], 0);
 501         }
 502
 503         khd->cur_domain = 0;
 504         khd->batching = 0;
 505
 506         hctx->sched_data = khd;
 507         kyber_depth_updated(hctx);
 508
 509         return 0;
 510
 511 err_kcqs:
 512         kfree(khd->kcqs);
 513 err_khd:
 514         kfree(khd);
 515         return -ENOMEM;
 516 }
 517
 518 static void kyber_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
 519 {
 520         struct kyber_hctx_data *khd = hctx->sched_data;
 521         int i;
 522
 523         for (i = 0; i < KYBER_NUM_DOMAINS; i++)
 524                 sbitmap_free(&khd->kcq_map[i]);
 525         kfree(khd->kcqs);
 526         kfree(hctx->sched_data);
 527 }
 528
 529 static int rq_get_domain_token(struct request *rq)
 530 {
 531         return (long)rq->elv.priv[0];
 532 }
 533
 534 static void rq_set_domain_token(struct request *rq, int token)
 535 {
 536         rq->elv.priv[0] = (void *)(long)token;
 537 }
 538
 539 static void rq_clear_domain_token(struct kyber_queue_data *kqd,
 540                                   struct request *rq)
 541 {
 542         unsigned int sched_domain;
 543         int nr;
 544
 545         nr = rq_get_domain_token(rq);
 546         if (nr != -1) {
 547                 sched_domain = kyber_sched_domain(rq->cmd_flags);
 548                 sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
 549                                     rq->mq_ctx->cpu);
 550         }
 551 }
 552
 553 static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
 554 {
 555         /*
 556          * We use the scheduler tags as per-hardware queue queueing tokens.
 557          * Async requests can be limited at this stage.
 558          */
 559         if (!op_is_sync(op)) {
 560                 struct kyber_queue_data *kqd = data->q->elevator->elevator_data;
 561
 562                 data->shallow_depth = kqd->async_depth;
 563         }
 564 }
 565
 566 static bool kyber_bio_merge(struct request_queue *q, struct bio *bio,
 567                 unsigned int nr_segs)
 568 {
 569         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
 570         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
 571         struct kyber_hctx_data *khd = hctx->sched_data;
 572         struct kyber_ctx_queue *kcq = &khd->kcqs[ctx->index_hw[hctx->type]];
 573         unsigned int sched_domain = kyber_sched_domain(bio->bi_opf);
 574         struct list_head *rq_list = &kcq->rq_list[sched_domain];
 575         bool merged;
 576
 577         spin_lock(&kcq->lock);
 578         merged = blk_bio_list_merge(hctx->queue, rq_list, bio, nr_segs);
 579         spin_unlock(&kcq->lock);
 580
 581         return merged;
 582 }
 583
 584 static void kyber_prepare_request(struct request *rq)
 585 {
 586         rq_set_domain_token(rq, -1);
 587 }
 588
 589 static void kyber_insert_requests(struct blk_mq_hw_ctx *hctx,
 590                                   struct list_head *rq_list, bool at_head)
 591 {
 592         struct kyber_hctx_data *khd = hctx->sched_data;
 593         struct request *rq, *next;
 594
 595         list_for_each_entry_safe(rq, next, rq_list, queuelist) {
 596                 unsigned int sched_domain = kyber_sched_domain(rq->cmd_flags);
 597                 struct kyber_ctx_queue *kcq = &khd->kcqs[rq->mq_ctx->index_hw[hctx->type]];
 598                 struct list_head *head = &kcq->rq_list[sched_domain];
 599
 600                 spin_lock(&kcq->lock);
 601                 trace_block_rq_insert(rq);
 602                 if (at_head)
 603                         list_move(&rq->queuelist, head);
 604                 else
 605                         list_move_tail(&rq->queuelist, head);
 606                 sbitmap_set_bit(&khd->kcq_map[sched_domain],
 607                                 rq->mq_ctx->index_hw[hctx->type]);
 608                 spin_unlock(&kcq->lock);
 609         }
 610 }
 611
 612 static void kyber_finish_request(struct request *rq)
 613 {
 614         struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
 615
 616         rq_clear_domain_token(kqd, rq);
 617 }
 618
 619 static void add_latency_sample(struct kyber_cpu_latency *cpu_latency,
 620                                unsigned int sched_domain, unsigned int type,
 621                                u64 target, u64 latency)
 622 {
 623         unsigned int bucket;
 624         u64 divisor;
 625
 626         if (latency > 0) {
 627                 divisor = max_t(u64, target >> KYBER_LATENCY_SHIFT, 1);
 628                 bucket = min_t(unsigned int, div64_u64(latency - 1, divisor),
 629                                KYBER_LATENCY_BUCKETS - 1);
 630         } else {
 631                 bucket = 0;
 632         }
 633
 634         atomic_inc(&cpu_latency->buckets[sched_domain][type][bucket]);
 635 }
 636
 637 static void kyber_completed_request(struct request *rq, u64 now)
 638 {
 639         struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
 640         struct kyber_cpu_latency *cpu_latency;
 641         unsigned int sched_domain;
 642         u64 target;
 643
 644         sched_domain = kyber_sched_domain(rq->cmd_flags);
 645         if (sched_domain == KYBER_OTHER)
 646                 return;
 647
 648         cpu_latency = get_cpu_ptr(kqd->cpu_latency);
 649         target = kqd->latency_targets[sched_domain];
 650         add_latency_sample(cpu_latency, sched_domain, KYBER_TOTAL_LATENCY,
 651                            target, now - rq->start_time_ns);
 652         add_latency_sample(cpu_latency, sched_domain, KYBER_IO_LATENCY, target,
 653                            now - rq->io_start_time_ns);
 654         put_cpu_ptr(kqd->cpu_latency);
 655
 656         timer_reduce(&kqd->timer, jiffies + HZ / 10);
 657 }
 658
 659 struct flush_kcq_data {
 660         struct kyber_hctx_data *khd;
 661         unsigned int sched_domain;
 662         struct list_head *list;
 663 };
 664
 665 static bool flush_busy_kcq(struct sbitmap *sb, unsigned int bitnr, void *data)
 666 {
 667         struct flush_kcq_data *flush_data = data;
 668         struct kyber_ctx_queue *kcq = &flush_data->khd->kcqs[bitnr];
 669
 670         spin_lock(&kcq->lock);
 671         list_splice_tail_init(&kcq->rq_list[flush_data->sched_domain],
 672                               flush_data->list);
 673         sbitmap_clear_bit(sb, bitnr);
 674         spin_unlock(&kcq->lock);
 675
 676         return true;
 677 }
 678
 679 static void kyber_flush_busy_kcqs(struct kyber_hctx_data *khd,
 680                                   unsigned int sched_domain,
 681                                   struct list_head *list)
 682 {
 683         struct flush_kcq_data data = {
 684                 .khd = khd,
 685                 .sched_domain = sched_domain,
 686                 .list = list,
 687         };
 688
 689         sbitmap_for_each_set(&khd->kcq_map[sched_domain],
 690                              flush_busy_kcq, &data);
 691 }
 692
 693 static int kyber_domain_wake(wait_queue_entry_t *wqe, unsigned mode, int flags,
 694                              void *key)
 695 {
 696         struct blk_mq_hw_ctx *hctx = READ_ONCE(wqe->private);
 697         struct sbq_wait *wait = container_of(wqe, struct sbq_wait, wait);
 698
 699         sbitmap_del_wait_queue(wait);
 700         blk_mq_run_hw_queue(hctx, true);
 701         return 1;
 702 }
 703
 704 static int kyber_get_domain_token(struct kyber_queue_data *kqd,
 705                                   struct kyber_hctx_data *khd,
 706                                   struct blk_mq_hw_ctx *hctx)
 707 {
 708         unsigned int sched_domain = khd->cur_domain;
 709         struct sbitmap_queue *domain_tokens = &kqd->domain_tokens[sched_domain];
 710         struct sbq_wait *wait = &khd->domain_wait[sched_domain];
 711         struct sbq_wait_state *ws;
 712         int nr;
 713
 714         nr = __sbitmap_queue_get(domain_tokens);
 715
 716         /*
 717          * If we failed to get a domain token, make sure the hardware queue is
 718          * run when one becomes available. Note that this is serialized on
 719          * khd->lock, but we still need to be careful about the waker.
 720          */
 721         if (nr < 0 && list_empty_careful(&wait->wait.entry)) {
 722                 ws = sbq_wait_ptr(domain_tokens,
 723                                   &khd->wait_index[sched_domain]);
 724                 khd->domain_ws[sched_domain] = ws;
 725                 sbitmap_add_wait_queue(domain_tokens, ws, wait);
 726
 727                 /*
 728                  * Try again in case a token was freed before we got on the wait
 729                  * queue.
 730                  */
 731                 nr = __sbitmap_queue_get(domain_tokens);
 732         }
 733
 734         /*
 735          * If we got a token while we were on the wait queue, remove ourselves
 736          * from the wait queue to ensure that all wake ups make forward
 737          * progress. It's possible that the waker already deleted the entry
 738          * between the !list_empty_careful() check and us grabbing the lock, but
 739          * list_del_init() is okay with that.
 740          */
 741         if (nr >= 0 && !list_empty_careful(&wait->wait.entry)) {
 742                 ws = khd->domain_ws[sched_domain];
 743                 spin_lock_irq(&ws->wait.lock);
 744                 sbitmap_del_wait_queue(wait);
 745                 spin_unlock_irq(&ws->wait.lock);
 746         }
 747
 748         return nr;
 749 }
 750
 751 static struct request *
 752 kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
 753                           struct kyber_hctx_data *khd,
 754                           struct blk_mq_hw_ctx *hctx)
 755 {
 756         struct list_head *rqs;
 757         struct request *rq;
 758         int nr;
 759
 760         rqs = &khd->rqs[khd->cur_domain];
 761
 762         /*
 763          * If we already have a flushed request, then we just need to get a
 764          * token for it. Otherwise, if there are pending requests in the kcqs,
 765          * flush the kcqs, but only if we can get a token. If not, we should
 766          * leave the requests in the kcqs so that they can be merged. Note that
 767          * khd->lock serializes the flushes, so if we observed any bit set in
 768          * the kcq_map, we will always get a request.
 769          */
 770         rq = list_first_entry_or_null(rqs, struct request, queuelist);
 771         if (rq) {
 772                 nr = kyber_get_domain_token(kqd, khd, hctx);
 773                 if (nr >= 0) {
 774                         khd->batching++;
 775                         rq_set_domain_token(rq, nr);
 776                         list_del_init(&rq->queuelist);
 777                         return rq;
 778                 } else {
 779                         trace_kyber_throttled(kqd->dev,
 780                                               kyber_domain_names[khd->cur_domain]);
 781                 }
 782         } else if (sbitmap_any_bit_set(&khd->kcq_map[khd->cur_domain])) {
 783                 nr = kyber_get_domain_token(kqd, khd, hctx);
 784                 if (nr >= 0) {
 785                         kyber_flush_busy_kcqs(khd, khd->cur_domain, rqs);
 786                         rq = list_first_entry(rqs, struct request, queuelist);
 787                         khd->batching++;
 788                         rq_set_domain_token(rq, nr);
 789                         list_del_init(&rq->queuelist);
 790                         return rq;
 791                 } else {
 792                         trace_kyber_throttled(kqd->dev,
 793                                               kyber_domain_names[khd->cur_domain]);
 794                 }
 795         }
 796
 797         /* There were either no pending requests or no tokens. */
 798         return NULL;
 799 }
 800
 801 static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
 802 {
 803         struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
 804         struct kyber_hctx_data *khd = hctx->sched_data;
 805         struct request *rq;
 806         int i;
 807
 808         spin_lock(&khd->lock);
 809
 810         /*
 811          * First, if we are still entitled to batch, try to dispatch a request
 812          * from the batch.
 813          */
 814         if (khd->batching < kyber_batch_size[khd->cur_domain]) {
 815                 rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
 816                 if (rq)
 817                         goto out;
 818         }
 819
 820         /*
 821          * Either,
 822          * 1. We were no longer entitled to a batch.
 823          * 2. The domain we were batching didn't have any requests.
 824          * 3. The domain we were batching was out of tokens.
 825          *
 826          * Start another batch. Note that this wraps back around to the original
 827          * domain if no other domains have requests or tokens.
 828          */
 829         khd->batching = 0;
 830         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
 831                 if (khd->cur_domain == KYBER_NUM_DOMAINS - 1)
 832                         khd->cur_domain = 0;
 833                 else
 834                         khd->cur_domain++;
 835
 836                 rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
 837                 if (rq)
 838                         goto out;
 839         }
 840
 841         rq = NULL;
 842 out:
 843         spin_unlock(&khd->lock);
 844         return rq;
 845 }
 846
 847 static bool kyber_has_work(struct blk_mq_hw_ctx *hctx)
 848 {
 849         struct kyber_hctx_data *khd = hctx->sched_data;
 850         int i;
 851
 852         for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
 853                 if (!list_empty_careful(&khd->rqs[i]) ||
 854                     sbitmap_any_bit_set(&khd->kcq_map[i]))
 855                         return true;
 856         }
 857
 858         return false;
 859 }
 860
 861 #define KYBER_LAT_SHOW_STORE(domain, name)                              \
 862 static ssize_t kyber_##name##_lat_show(struct elevator_queue *e,        \
 863                                        char *page)                      \
 864 {                                                                       \
 865         struct kyber_queue_data *kqd = e->elevator_data;                \
 866                                                                         \
 867         return sprintf(page, "%llu\n", kqd->latency_targets[domain]);   \
 868 }                                                                       \
 869                                                                         \
 870 static ssize_t kyber_##name##_lat_store(struct elevator_queue *e,       \
 871                                         const char *page, size_t count) \
 872 {                                                                       \
 873         struct kyber_queue_data *kqd = e->elevator_data;                \
 874         unsigned long long nsec;                                        \
 875         int ret;                                                        \
 876                                                                         \
 877         ret = kstrtoull(page, 10, &nsec);                               \
 878         if (ret)                                                        \
 879                 return ret;                                             \
 880                                                                         \
 881         kqd->latency_targets[domain] = nsec;                            \
 882                                                                         \
 883         return count;                                                   \
 884 }
 885 KYBER_LAT_SHOW_STORE(KYBER_READ, read);
 886 KYBER_LAT_SHOW_STORE(KYBER_WRITE, write);
 887 #undef KYBER_LAT_SHOW_STORE
 888
 889 #define KYBER_LAT_ATTR(op) __ATTR(op##_lat_nsec, 0644, kyber_##op##_lat_show, kyber_##op##_lat_store)
 890 static struct elv_fs_entry kyber_sched_attrs[] = {
 891         KYBER_LAT_ATTR(read),
 892         KYBER_LAT_ATTR(write),
 893         __ATTR_NULL
 894 };
 895 #undef KYBER_LAT_ATTR
 896
 897 #ifdef CONFIG_BLK_DEBUG_FS
 898 #define KYBER_DEBUGFS_DOMAIN_ATTRS(domain, name)                        \
 899 static int kyber_##name##_tokens_show(void *data, struct seq_file *m)   \
 900 {                                                                       \
 901         struct request_queue *q = data;                                 \
 902         struct kyber_queue_data *kqd = q->elevator->elevator_data;      \
 903                                                                         \
 904         sbitmap_queue_show(&kqd->domain_tokens[domain], m);             \
 905         return 0;                                                       \
 906 }                                                                       \
 907                                                                         \
 908 static void *kyber_##name##_rqs_start(struct seq_file *m, loff_t *pos)  \
 909         __acquires(&khd->lock)                                          \
 910 {                                                                       \
 911         struct blk_mq_hw_ctx *hctx = m->private;                        \
 912         struct kyber_hctx_data *khd = hctx->sched_data;                 \
 913                                                                         \
 914         spin_lock(&khd->lock);                                          \
 915         return seq_list_start(&khd->rqs[domain], *pos);                 \
 916 }                                                                       \
 917                                                                         \
 918 static void *kyber_##name##_rqs_next(struct seq_file *m, void *v,       \
 919                                      loff_t *pos)                       \
 920 {                                                                       \
 921         struct blk_mq_hw_ctx *hctx = m->private;                        \
 922         struct kyber_hctx_data *khd = hctx->sched_data;                 \
 923                                                                         \
 924         return seq_list_next(v, &khd->rqs[domain], pos);                \
 925 }                                                                       \
 926                                                                         \
 927 static void kyber_##name##_rqs_stop(struct seq_file *m, void *v)        \
 928         __releases(&khd->lock)                                          \
 929 {                                                                       \
 930         struct blk_mq_hw_ctx *hctx = m->private;                        \
 931         struct kyber_hctx_data *khd = hctx->sched_data;                 \
 932                                                                         \
 933         spin_unlock(&khd->lock);                                        \
 934 }                                                                       \
 935                                                                         \
 936 static const struct seq_operations kyber_##name##_rqs_seq_ops = {       \
 937         .start  = kyber_##name##_rqs_start,                             \
 938         .next   = kyber_##name##_rqs_next,                              \
 939         .stop   = kyber_##name##_rqs_stop,                              \
 940         .show   = blk_mq_debugfs_rq_show,                               \
 941 };                                                                      \
 942                                                                         \
 943 static int kyber_##name##_waiting_show(void *data, struct seq_file *m)  \
 944 {                                                                       \
 945         struct blk_mq_hw_ctx *hctx = data;                              \
 946         struct kyber_hctx_data *khd = hctx->sched_data;                 \
 947         wait_queue_entry_t *wait = &khd->domain_wait[domain].wait;      \
 948                                                                         \
 949         seq_printf(m, "%d\n", !list_empty_careful(&wait->entry));       \
 950         return 0;                                                       \
 951 }
 952 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_READ, read)
 953 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_WRITE, write)
 954 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_DISCARD, discard)
 955 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_OTHER, other)
 956 #undef KYBER_DEBUGFS_DOMAIN_ATTRS
 957
 958 static int kyber_async_depth_show(void *data, struct seq_file *m)
 959 {
 960         struct request_queue *q = data;
 961         struct kyber_queue_data *kqd = q->elevator->elevator_data;
 962
 963         seq_printf(m, "%u\n", kqd->async_depth);
 964         return 0;
 965 }
 966
 967 static int kyber_cur_domain_show(void *data, struct seq_file *m)
 968 {
 969         struct blk_mq_hw_ctx *hctx = data;
 970         struct kyber_hctx_data *khd = hctx->sched_data;
 971
 972         seq_printf(m, "%s\n", kyber_domain_names[khd->cur_domain]);
 973         return 0;
 974 }
 975
 976 static int kyber_batching_show(void *data, struct seq_file *m)
 977 {
 978         struct blk_mq_hw_ctx *hctx = data;
 979         struct kyber_hctx_data *khd = hctx->sched_data;
 980
 981         seq_printf(m, "%u\n", khd->batching);
 982         return 0;
 983 }
 984
 985 #define KYBER_QUEUE_DOMAIN_ATTRS(name)  \
 986         {#name "_tokens", 0400, kyber_##name##_tokens_show}
 987 static const struct blk_mq_debugfs_attr kyber_queue_debugfs_attrs[] = {
 988         KYBER_QUEUE_DOMAIN_ATTRS(read),
 989         KYBER_QUEUE_DOMAIN_ATTRS(write),
 990         KYBER_QUEUE_DOMAIN_ATTRS(discard),
 991         KYBER_QUEUE_DOMAIN_ATTRS(other),
 992         {"async_depth", 0400, kyber_async_depth_show},
 993         {},
 994 };
 995 #undef KYBER_QUEUE_DOMAIN_ATTRS
 996
 997 #define KYBER_HCTX_DOMAIN_ATTRS(name)                                   \
 998         {#name "_rqs", 0400, .seq_ops = &kyber_##name##_rqs_seq_ops},   \
 999         {#name "_waiting", 0400, kyber_##name##_waiting_show}
1000 static const struct blk_mq_debugfs_attr kyber_hctx_debugfs_attrs[] = {
1001         KYBER_HCTX_DOMAIN_ATTRS(read),
1002         KYBER_HCTX_DOMAIN_ATTRS(write),
1003         KYBER_HCTX_DOMAIN_ATTRS(discard),
1004         KYBER_HCTX_DOMAIN_ATTRS(other),
1005         {"cur_domain", 0400, kyber_cur_domain_show},
1006         {"batching", 0400, kyber_batching_show},
1007         {},
1008 };
1009 #undef KYBER_HCTX_DOMAIN_ATTRS
1010 #endif
1011
1012 static struct elevator_type kyber_sched = {
1013         .ops = {
1014                 .init_sched = kyber_init_sched,
1015                 .exit_sched = kyber_exit_sched,
1016                 .init_hctx = kyber_init_hctx,
1017                 .exit_hctx = kyber_exit_hctx,
1018                 .limit_depth = kyber_limit_depth,
1019                 .bio_merge = kyber_bio_merge,
1020                 .prepare_request = kyber_prepare_request,
1021                 .insert_requests = kyber_insert_requests,
1022                 .finish_request = kyber_finish_request,
1023                 .requeue_request = kyber_finish_request,
1024                 .completed_request = kyber_completed_request,
1025                 .dispatch_request = kyber_dispatch_request,
1026                 .has_work = kyber_has_work,
1027                 .depth_updated = kyber_depth_updated,
1028         },
1029 #ifdef CONFIG_BLK_DEBUG_FS
1030         .queue_debugfs_attrs = kyber_queue_debugfs_attrs,
1031         .hctx_debugfs_attrs = kyber_hctx_debugfs_attrs,
1032 #endif
1033         .elevator_attrs = kyber_sched_attrs,
1034         .elevator_name = "kyber",
1035         .elevator_features = ELEVATOR_F_MQ_AWARE,
1036         .elevator_owner = THIS_MODULE,
1037 };
1038
1039 static int __init kyber_init(void)
1040 {
1041         return elv_register(&kyber_sched);
1042 }
1043
1044 static void __exit kyber_exit(void)
1045 {
1046         elv_unregister(&kyber_sched);
1047 }
1048
1049 module_init(kyber_init);
1050 module_exit(kyber_exit);
1051
1052 MODULE_AUTHOR("Omar Sandoval");
1053 MODULE_LICENSE("GPL");
1054 MODULE_DESCRIPTION("Kyber I/O scheduler");