1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Block rq-qos base io controller 4 * 5 * This works similar to wbt with a few exceptions 6 * 7 * - It's bio based, so the latency covers the whole block layer in addition to 8 * the actual io. 9 * - We will throttle all IO that comes in here if we need to. 10 * - We use the mean latency over the 100ms window. This is because writes can 11 * be particularly fast, which could give us a false sense of the impact of 12 * other workloads on our protected workload. 13 * - By default there's no throttling, we set the queue_depth to UINT_MAX so 14 * that we can have as many outstanding bio's as we're allowed to. Only at 15 * throttle time do we pay attention to the actual queue depth. 16 * 17 * The hierarchy works like the cpu controller does, we track the latency at 18 * every configured node, and each configured node has it's own independent 19 * queue depth. This means that we only care about our latency targets at the 20 * peer level. Some group at the bottom of the hierarchy isn't going to affect 21 * a group at the end of some other path if we're only configred at leaf level. 22 * 23 * Consider the following 24 * 25 * root blkg 26 * / \ 27 * fast (target=5ms) slow (target=10ms) 28 * / \ / \ 29 * a b normal(15ms) unloved 30 * 31 * "a" and "b" have no target, but their combined io under "fast" cannot exceed 32 * an average latency of 5ms. If it does then we will throttle the "slow" 33 * group. In the case of "normal", if it exceeds its 15ms target, we will 34 * throttle "unloved", but nobody else. 35 * 36 * In this example "fast", "slow", and "normal" will be the only groups actually 37 * accounting their io latencies. We have to walk up the heirarchy to the root 38 * on every submit and complete so we can do the appropriate stat recording and 39 * adjust the queue depth of ourselves if needed. 40 * 41 * There are 2 ways we throttle IO. 42 * 43 * 1) Queue depth throttling. As we throttle down we will adjust the maximum 44 * number of IO's we're allowed to have in flight. This starts at (u64)-1 down 45 * to 1. If the group is only ever submitting IO for itself then this is the 46 * only way we throttle. 47 * 48 * 2) Induced delay throttling. This is for the case that a group is generating 49 * IO that has to be issued by the root cg to avoid priority inversion. So think 50 * REQ_META or REQ_SWAP. If we are already at qd == 1 and we're getting a lot 51 * of work done for us on behalf of the root cg and are being asked to scale 52 * down more then we induce a latency at userspace return. We accumulate the 53 * total amount of time we need to be punished by doing 54 * 55 * total_time += min_lat_nsec - actual_io_completion 56 * 57 * and then at throttle time will do 58 * 59 * throttle_time = min(total_time, NSEC_PER_SEC) 60 * 61 * This induced delay will throttle back the activity that is generating the 62 * root cg issued io's, wethere that's some metadata intensive operation or the 63 * group is using so much memory that it is pushing us into swap. 64 * 65 * Copyright (C) 2018 Josef Bacik 66 */ 67 #include <linux/kernel.h> 68 #include <linux/blk_types.h> 69 #include <linux/backing-dev.h> 70 #include <linux/module.h> 71 #include <linux/timer.h> 72 #include <linux/memcontrol.h> 73 #include <linux/sched/loadavg.h> 74 #include <linux/sched/signal.h> 75 #include <trace/events/block.h> 76 #include <linux/blk-mq.h> 77 #include "blk-rq-qos.h" 78 #include "blk-stat.h" 79 #include "blk-cgroup.h" 80 #include "blk.h" 81 82 #define DEFAULT_SCALE_COOKIE 1000000U 83 84 static struct blkcg_policy blkcg_policy_iolatency; 85 struct iolatency_grp; 86 87 struct blk_iolatency { 88 struct rq_qos rqos; 89 struct timer_list timer; 90 91 /* 92 * ->enabled is the master enable switch gating the throttling logic and 93 * inflight tracking. The number of cgroups which have iolat enabled is 94 * tracked in ->enable_cnt, and ->enable is flipped on/off accordingly 95 * from ->enable_work with the request_queue frozen. For details, See 96 * blkiolatency_enable_work_fn(). 97 */ 98 bool enabled; 99 atomic_t enable_cnt; 100 struct work_struct enable_work; 101 }; 102 103 static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos) 104 { 105 return container_of(rqos, struct blk_iolatency, rqos); 106 } 107 108 struct child_latency_info { 109 spinlock_t lock; 110 111 /* Last time we adjusted the scale of everybody. */ 112 u64 last_scale_event; 113 114 /* The latency that we missed. */ 115 u64 scale_lat; 116 117 /* Total io's from all of our children for the last summation. */ 118 u64 nr_samples; 119 120 /* The guy who actually changed the latency numbers. */ 121 struct iolatency_grp *scale_grp; 122 123 /* Cookie to tell if we need to scale up or down. */ 124 atomic_t scale_cookie; 125 }; 126 127 struct percentile_stats { 128 u64 total; 129 u64 missed; 130 }; 131 132 struct latency_stat { 133 union { 134 struct percentile_stats ps; 135 struct blk_rq_stat rqs; 136 }; 137 }; 138 139 struct iolatency_grp { 140 struct blkg_policy_data pd; 141 struct latency_stat __percpu *stats; 142 struct latency_stat cur_stat; 143 struct blk_iolatency *blkiolat; 144 unsigned int max_depth; 145 struct rq_wait rq_wait; 146 atomic64_t window_start; 147 atomic_t scale_cookie; 148 u64 min_lat_nsec; 149 u64 cur_win_nsec; 150 151 /* total running average of our io latency. */ 152 u64 lat_avg; 153 154 /* Our current number of IO's for the last summation. */ 155 u64 nr_samples; 156 157 bool ssd; 158 struct child_latency_info child_lat; 159 }; 160 161 #define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC) 162 #define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC 163 /* 164 * These are the constants used to fake the fixed-point moving average 165 * calculation just like load average. The call to calc_load() folds 166 * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg. The sampling 167 * window size is bucketed to try to approximately calculate average 168 * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows 169 * elapse immediately. Note, windows only elapse with IO activity. Idle 170 * periods extend the most recent window. 171 */ 172 #define BLKIOLATENCY_NR_EXP_FACTORS 5 173 #define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \ 174 (BLKIOLATENCY_NR_EXP_FACTORS - 1)) 175 static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = { 176 2045, // exp(1/600) - 600 samples 177 2039, // exp(1/240) - 240 samples 178 2031, // exp(1/120) - 120 samples 179 2023, // exp(1/80) - 80 samples 180 2014, // exp(1/60) - 60 samples 181 }; 182 183 static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd) 184 { 185 return pd ? container_of(pd, struct iolatency_grp, pd) : NULL; 186 } 187 188 static inline struct iolatency_grp *blkg_to_lat(struct blkcg_gq *blkg) 189 { 190 return pd_to_lat(blkg_to_pd(blkg, &blkcg_policy_iolatency)); 191 } 192 193 static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat) 194 { 195 return pd_to_blkg(&iolat->pd); 196 } 197 198 static inline void latency_stat_init(struct iolatency_grp *iolat, 199 struct latency_stat *stat) 200 { 201 if (iolat->ssd) { 202 stat->ps.total = 0; 203 stat->ps.missed = 0; 204 } else 205 blk_rq_stat_init(&stat->rqs); 206 } 207 208 static inline void latency_stat_sum(struct iolatency_grp *iolat, 209 struct latency_stat *sum, 210 struct latency_stat *stat) 211 { 212 if (iolat->ssd) { 213 sum->ps.total += stat->ps.total; 214 sum->ps.missed += stat->ps.missed; 215 } else 216 blk_rq_stat_sum(&sum->rqs, &stat->rqs); 217 } 218 219 static inline void latency_stat_record_time(struct iolatency_grp *iolat, 220 u64 req_time) 221 { 222 struct latency_stat *stat = get_cpu_ptr(iolat->stats); 223 if (iolat->ssd) { 224 if (req_time >= iolat->min_lat_nsec) 225 stat->ps.missed++; 226 stat->ps.total++; 227 } else 228 blk_rq_stat_add(&stat->rqs, req_time); 229 put_cpu_ptr(stat); 230 } 231 232 static inline bool latency_sum_ok(struct iolatency_grp *iolat, 233 struct latency_stat *stat) 234 { 235 if (iolat->ssd) { 236 u64 thresh = div64_u64(stat->ps.total, 10); 237 thresh = max(thresh, 1ULL); 238 return stat->ps.missed < thresh; 239 } 240 return stat->rqs.mean <= iolat->min_lat_nsec; 241 } 242 243 static inline u64 latency_stat_samples(struct iolatency_grp *iolat, 244 struct latency_stat *stat) 245 { 246 if (iolat->ssd) 247 return stat->ps.total; 248 return stat->rqs.nr_samples; 249 } 250 251 static inline void iolat_update_total_lat_avg(struct iolatency_grp *iolat, 252 struct latency_stat *stat) 253 { 254 int exp_idx; 255 256 if (iolat->ssd) 257 return; 258 259 /* 260 * calc_load() takes in a number stored in fixed point representation. 261 * Because we are using this for IO time in ns, the values stored 262 * are significantly larger than the FIXED_1 denominator (2048). 263 * Therefore, rounding errors in the calculation are negligible and 264 * can be ignored. 265 */ 266 exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1, 267 div64_u64(iolat->cur_win_nsec, 268 BLKIOLATENCY_EXP_BUCKET_SIZE)); 269 iolat->lat_avg = calc_load(iolat->lat_avg, 270 iolatency_exp_factors[exp_idx], 271 stat->rqs.mean); 272 } 273 274 static void iolat_cleanup_cb(struct rq_wait *rqw, void *private_data) 275 { 276 atomic_dec(&rqw->inflight); 277 wake_up(&rqw->wait); 278 } 279 280 static bool iolat_acquire_inflight(struct rq_wait *rqw, void *private_data) 281 { 282 struct iolatency_grp *iolat = private_data; 283 return rq_wait_inc_below(rqw, iolat->max_depth); 284 } 285 286 static void __blkcg_iolatency_throttle(struct rq_qos *rqos, 287 struct iolatency_grp *iolat, 288 bool issue_as_root, 289 bool use_memdelay) 290 { 291 struct rq_wait *rqw = &iolat->rq_wait; 292 unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay); 293 294 if (use_delay) 295 blkcg_schedule_throttle(rqos->q->disk, use_memdelay); 296 297 /* 298 * To avoid priority inversions we want to just take a slot if we are 299 * issuing as root. If we're being killed off there's no point in 300 * delaying things, we may have been killed by OOM so throttling may 301 * make recovery take even longer, so just let the IO's through so the 302 * task can go away. 303 */ 304 if (issue_as_root || fatal_signal_pending(current)) { 305 atomic_inc(&rqw->inflight); 306 return; 307 } 308 309 rq_qos_wait(rqw, iolat, iolat_acquire_inflight, iolat_cleanup_cb); 310 } 311 312 #define SCALE_DOWN_FACTOR 2 313 #define SCALE_UP_FACTOR 4 314 315 static inline unsigned long scale_amount(unsigned long qd, bool up) 316 { 317 return max(up ? qd >> SCALE_UP_FACTOR : qd >> SCALE_DOWN_FACTOR, 1UL); 318 } 319 320 /* 321 * We scale the qd down faster than we scale up, so we need to use this helper 322 * to adjust the scale_cookie accordingly so we don't prematurely get 323 * scale_cookie at DEFAULT_SCALE_COOKIE and unthrottle too much. 324 * 325 * Each group has their own local copy of the last scale cookie they saw, so if 326 * the global scale cookie goes up or down they know which way they need to go 327 * based on their last knowledge of it. 328 */ 329 static void scale_cookie_change(struct blk_iolatency *blkiolat, 330 struct child_latency_info *lat_info, 331 bool up) 332 { 333 unsigned long qd = blkiolat->rqos.q->nr_requests; 334 unsigned long scale = scale_amount(qd, up); 335 unsigned long old = atomic_read(&lat_info->scale_cookie); 336 unsigned long max_scale = qd << 1; 337 unsigned long diff = 0; 338 339 if (old < DEFAULT_SCALE_COOKIE) 340 diff = DEFAULT_SCALE_COOKIE - old; 341 342 if (up) { 343 if (scale + old > DEFAULT_SCALE_COOKIE) 344 atomic_set(&lat_info->scale_cookie, 345 DEFAULT_SCALE_COOKIE); 346 else if (diff > qd) 347 atomic_inc(&lat_info->scale_cookie); 348 else 349 atomic_add(scale, &lat_info->scale_cookie); 350 } else { 351 /* 352 * We don't want to dig a hole so deep that it takes us hours to 353 * dig out of it. Just enough that we don't throttle/unthrottle 354 * with jagged workloads but can still unthrottle once pressure 355 * has sufficiently dissipated. 356 */ 357 if (diff > qd) { 358 if (diff < max_scale) 359 atomic_dec(&lat_info->scale_cookie); 360 } else { 361 atomic_sub(scale, &lat_info->scale_cookie); 362 } 363 } 364 } 365 366 /* 367 * Change the queue depth of the iolatency_grp. We add 1/16th of the 368 * queue depth at a time so we don't get wild swings and hopefully dial in to 369 * fairer distribution of the overall queue depth. We halve the queue depth 370 * at a time so we can scale down queue depth quickly from default unlimited 371 * to target. 372 */ 373 static void scale_change(struct iolatency_grp *iolat, bool up) 374 { 375 unsigned long qd = iolat->blkiolat->rqos.q->nr_requests; 376 unsigned long scale = scale_amount(qd, up); 377 unsigned long old = iolat->max_depth; 378 379 if (old > qd) 380 old = qd; 381 382 if (up) { 383 if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat))) 384 return; 385 386 if (old < qd) { 387 old += scale; 388 old = min(old, qd); 389 iolat->max_depth = old; 390 wake_up_all(&iolat->rq_wait.wait); 391 } 392 } else { 393 old >>= 1; 394 iolat->max_depth = max(old, 1UL); 395 } 396 } 397 398 /* Check our parent and see if the scale cookie has changed. */ 399 static void check_scale_change(struct iolatency_grp *iolat) 400 { 401 struct iolatency_grp *parent; 402 struct child_latency_info *lat_info; 403 unsigned int cur_cookie; 404 unsigned int our_cookie = atomic_read(&iolat->scale_cookie); 405 u64 scale_lat; 406 int direction = 0; 407 408 parent = blkg_to_lat(lat_to_blkg(iolat)->parent); 409 if (!parent) 410 return; 411 412 lat_info = &parent->child_lat; 413 cur_cookie = atomic_read(&lat_info->scale_cookie); 414 scale_lat = READ_ONCE(lat_info->scale_lat); 415 416 if (cur_cookie < our_cookie) 417 direction = -1; 418 else if (cur_cookie > our_cookie) 419 direction = 1; 420 else 421 return; 422 423 if (!atomic_try_cmpxchg(&iolat->scale_cookie, &our_cookie, cur_cookie)) { 424 /* Somebody beat us to the punch, just bail. */ 425 return; 426 } 427 428 if (direction < 0 && iolat->min_lat_nsec) { 429 u64 samples_thresh; 430 431 if (!scale_lat || iolat->min_lat_nsec <= scale_lat) 432 return; 433 434 /* 435 * Sometimes high priority groups are their own worst enemy, so 436 * instead of taking it out on some poor other group that did 5% 437 * or less of the IO's for the last summation just skip this 438 * scale down event. 439 */ 440 samples_thresh = lat_info->nr_samples * 5; 441 samples_thresh = max(1ULL, div64_u64(samples_thresh, 100)); 442 if (iolat->nr_samples <= samples_thresh) 443 return; 444 } 445 446 /* We're as low as we can go. */ 447 if (iolat->max_depth == 1 && direction < 0) { 448 blkcg_use_delay(lat_to_blkg(iolat)); 449 return; 450 } 451 452 /* We're back to the default cookie, unthrottle all the things. */ 453 if (cur_cookie == DEFAULT_SCALE_COOKIE) { 454 blkcg_clear_delay(lat_to_blkg(iolat)); 455 iolat->max_depth = UINT_MAX; 456 wake_up_all(&iolat->rq_wait.wait); 457 return; 458 } 459 460 scale_change(iolat, direction > 0); 461 } 462 463 static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) 464 { 465 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 466 struct blkcg_gq *blkg = bio->bi_blkg; 467 bool issue_as_root = bio_issue_as_root_blkg(bio); 468 469 if (!blkiolat->enabled) 470 return; 471 472 while (blkg && blkg->parent) { 473 struct iolatency_grp *iolat = blkg_to_lat(blkg); 474 if (!iolat) { 475 blkg = blkg->parent; 476 continue; 477 } 478 479 check_scale_change(iolat); 480 __blkcg_iolatency_throttle(rqos, iolat, issue_as_root, 481 (bio->bi_opf & REQ_SWAP) == REQ_SWAP); 482 blkg = blkg->parent; 483 } 484 if (!timer_pending(&blkiolat->timer)) 485 mod_timer(&blkiolat->timer, jiffies + HZ); 486 } 487 488 static void iolatency_record_time(struct iolatency_grp *iolat, 489 struct bio_issue *issue, u64 now, 490 bool issue_as_root) 491 { 492 u64 start = bio_issue_time(issue); 493 u64 req_time; 494 495 /* 496 * Have to do this so we are truncated to the correct time that our 497 * issue is truncated to. 498 */ 499 now = __bio_issue_time(now); 500 501 if (now <= start) 502 return; 503 504 req_time = now - start; 505 506 /* 507 * We don't want to count issue_as_root bio's in the cgroups latency 508 * statistics as it could skew the numbers downwards. 509 */ 510 if (unlikely(issue_as_root && iolat->max_depth != UINT_MAX)) { 511 u64 sub = iolat->min_lat_nsec; 512 if (req_time < sub) 513 blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time); 514 return; 515 } 516 517 latency_stat_record_time(iolat, req_time); 518 } 519 520 #define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC) 521 #define BLKIOLATENCY_MIN_GOOD_SAMPLES 5 522 523 static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now) 524 { 525 struct blkcg_gq *blkg = lat_to_blkg(iolat); 526 struct iolatency_grp *parent; 527 struct child_latency_info *lat_info; 528 struct latency_stat stat; 529 unsigned long flags; 530 int cpu; 531 532 latency_stat_init(iolat, &stat); 533 preempt_disable(); 534 for_each_online_cpu(cpu) { 535 struct latency_stat *s; 536 s = per_cpu_ptr(iolat->stats, cpu); 537 latency_stat_sum(iolat, &stat, s); 538 latency_stat_init(iolat, s); 539 } 540 preempt_enable(); 541 542 parent = blkg_to_lat(blkg->parent); 543 if (!parent) 544 return; 545 546 lat_info = &parent->child_lat; 547 548 iolat_update_total_lat_avg(iolat, &stat); 549 550 /* Everything is ok and we don't need to adjust the scale. */ 551 if (latency_sum_ok(iolat, &stat) && 552 atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE) 553 return; 554 555 /* Somebody beat us to the punch, just bail. */ 556 spin_lock_irqsave(&lat_info->lock, flags); 557 558 latency_stat_sum(iolat, &iolat->cur_stat, &stat); 559 lat_info->nr_samples -= iolat->nr_samples; 560 lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat); 561 iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat); 562 563 if ((lat_info->last_scale_event >= now || 564 now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME)) 565 goto out; 566 567 if (latency_sum_ok(iolat, &iolat->cur_stat) && 568 latency_sum_ok(iolat, &stat)) { 569 if (latency_stat_samples(iolat, &iolat->cur_stat) < 570 BLKIOLATENCY_MIN_GOOD_SAMPLES) 571 goto out; 572 if (lat_info->scale_grp == iolat) { 573 lat_info->last_scale_event = now; 574 scale_cookie_change(iolat->blkiolat, lat_info, true); 575 } 576 } else if (lat_info->scale_lat == 0 || 577 lat_info->scale_lat >= iolat->min_lat_nsec) { 578 lat_info->last_scale_event = now; 579 if (!lat_info->scale_grp || 580 lat_info->scale_lat > iolat->min_lat_nsec) { 581 WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec); 582 lat_info->scale_grp = iolat; 583 } 584 scale_cookie_change(iolat->blkiolat, lat_info, false); 585 } 586 latency_stat_init(iolat, &iolat->cur_stat); 587 out: 588 spin_unlock_irqrestore(&lat_info->lock, flags); 589 } 590 591 static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) 592 { 593 struct blkcg_gq *blkg; 594 struct rq_wait *rqw; 595 struct iolatency_grp *iolat; 596 u64 window_start; 597 u64 now; 598 bool issue_as_root = bio_issue_as_root_blkg(bio); 599 int inflight = 0; 600 601 blkg = bio->bi_blkg; 602 if (!blkg || !bio_flagged(bio, BIO_QOS_THROTTLED)) 603 return; 604 605 iolat = blkg_to_lat(bio->bi_blkg); 606 if (!iolat) 607 return; 608 609 if (!iolat->blkiolat->enabled) 610 return; 611 612 now = ktime_to_ns(ktime_get()); 613 while (blkg && blkg->parent) { 614 iolat = blkg_to_lat(blkg); 615 if (!iolat) { 616 blkg = blkg->parent; 617 continue; 618 } 619 rqw = &iolat->rq_wait; 620 621 inflight = atomic_dec_return(&rqw->inflight); 622 WARN_ON_ONCE(inflight < 0); 623 /* 624 * If bi_status is BLK_STS_AGAIN, the bio wasn't actually 625 * submitted, so do not account for it. 626 */ 627 if (iolat->min_lat_nsec && bio->bi_status != BLK_STS_AGAIN) { 628 iolatency_record_time(iolat, &bio->bi_issue, now, 629 issue_as_root); 630 window_start = atomic64_read(&iolat->window_start); 631 if (now > window_start && 632 (now - window_start) >= iolat->cur_win_nsec) { 633 if (atomic64_try_cmpxchg(&iolat->window_start, 634 &window_start, now)) 635 iolatency_check_latencies(iolat, now); 636 } 637 } 638 wake_up(&rqw->wait); 639 blkg = blkg->parent; 640 } 641 } 642 643 static void blkcg_iolatency_exit(struct rq_qos *rqos) 644 { 645 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 646 647 timer_shutdown_sync(&blkiolat->timer); 648 flush_work(&blkiolat->enable_work); 649 blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency); 650 kfree(blkiolat); 651 } 652 653 static struct rq_qos_ops blkcg_iolatency_ops = { 654 .throttle = blkcg_iolatency_throttle, 655 .done_bio = blkcg_iolatency_done_bio, 656 .exit = blkcg_iolatency_exit, 657 }; 658 659 static void blkiolatency_timer_fn(struct timer_list *t) 660 { 661 struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer); 662 struct blkcg_gq *blkg; 663 struct cgroup_subsys_state *pos_css; 664 u64 now = ktime_to_ns(ktime_get()); 665 666 rcu_read_lock(); 667 blkg_for_each_descendant_pre(blkg, pos_css, 668 blkiolat->rqos.q->root_blkg) { 669 struct iolatency_grp *iolat; 670 struct child_latency_info *lat_info; 671 unsigned long flags; 672 u64 cookie; 673 674 /* 675 * We could be exiting, don't access the pd unless we have a 676 * ref on the blkg. 677 */ 678 if (!blkg_tryget(blkg)) 679 continue; 680 681 iolat = blkg_to_lat(blkg); 682 if (!iolat) 683 goto next; 684 685 lat_info = &iolat->child_lat; 686 cookie = atomic_read(&lat_info->scale_cookie); 687 688 if (cookie >= DEFAULT_SCALE_COOKIE) 689 goto next; 690 691 spin_lock_irqsave(&lat_info->lock, flags); 692 if (lat_info->last_scale_event >= now) 693 goto next_lock; 694 695 /* 696 * We scaled down but don't have a scale_grp, scale up and carry 697 * on. 698 */ 699 if (lat_info->scale_grp == NULL) { 700 scale_cookie_change(iolat->blkiolat, lat_info, true); 701 goto next_lock; 702 } 703 704 /* 705 * It's been 5 seconds since our last scale event, clear the 706 * scale grp in case the group that needed the scale down isn't 707 * doing any IO currently. 708 */ 709 if (now - lat_info->last_scale_event >= 710 ((u64)NSEC_PER_SEC * 5)) 711 lat_info->scale_grp = NULL; 712 next_lock: 713 spin_unlock_irqrestore(&lat_info->lock, flags); 714 next: 715 blkg_put(blkg); 716 } 717 rcu_read_unlock(); 718 } 719 720 /** 721 * blkiolatency_enable_work_fn - Enable or disable iolatency on the device 722 * @work: enable_work of the blk_iolatency of interest 723 * 724 * iolatency needs to keep track of the number of in-flight IOs per cgroup. This 725 * is relatively expensive as it involves walking up the hierarchy twice for 726 * every IO. Thus, if iolatency is not enabled in any cgroup for the device, we 727 * want to disable the in-flight tracking. 728 * 729 * We have to make sure that the counting is balanced - we don't want to leak 730 * the in-flight counts by disabling accounting in the completion path while IOs 731 * are in flight. This is achieved by ensuring that no IO is in flight by 732 * freezing the queue while flipping ->enabled. As this requires a sleepable 733 * context, ->enabled flipping is punted to this work function. 734 */ 735 static void blkiolatency_enable_work_fn(struct work_struct *work) 736 { 737 struct blk_iolatency *blkiolat = container_of(work, struct blk_iolatency, 738 enable_work); 739 bool enabled; 740 741 /* 742 * There can only be one instance of this function running for @blkiolat 743 * and it's guaranteed to be executed at least once after the latest 744 * ->enabled_cnt modification. Acting on the latest ->enable_cnt is 745 * sufficient. 746 * 747 * Also, we know @blkiolat is safe to access as ->enable_work is flushed 748 * in blkcg_iolatency_exit(). 749 */ 750 enabled = atomic_read(&blkiolat->enable_cnt); 751 if (enabled != blkiolat->enabled) { 752 blk_mq_freeze_queue(blkiolat->rqos.q); 753 blkiolat->enabled = enabled; 754 blk_mq_unfreeze_queue(blkiolat->rqos.q); 755 } 756 } 757 758 int blk_iolatency_init(struct gendisk *disk) 759 { 760 struct request_queue *q = disk->queue; 761 struct blk_iolatency *blkiolat; 762 struct rq_qos *rqos; 763 int ret; 764 765 blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL); 766 if (!blkiolat) 767 return -ENOMEM; 768 769 rqos = &blkiolat->rqos; 770 rqos->id = RQ_QOS_LATENCY; 771 rqos->ops = &blkcg_iolatency_ops; 772 rqos->q = q; 773 774 ret = rq_qos_add(q, rqos); 775 if (ret) 776 goto err_free; 777 ret = blkcg_activate_policy(q, &blkcg_policy_iolatency); 778 if (ret) 779 goto err_qos_del; 780 781 timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0); 782 INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn); 783 784 return 0; 785 786 err_qos_del: 787 rq_qos_del(q, rqos); 788 err_free: 789 kfree(blkiolat); 790 return ret; 791 } 792 793 static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) 794 { 795 struct iolatency_grp *iolat = blkg_to_lat(blkg); 796 struct blk_iolatency *blkiolat = iolat->blkiolat; 797 u64 oldval = iolat->min_lat_nsec; 798 799 iolat->min_lat_nsec = val; 800 iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE); 801 iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, 802 BLKIOLATENCY_MAX_WIN_SIZE); 803 804 if (!oldval && val) { 805 if (atomic_inc_return(&blkiolat->enable_cnt) == 1) 806 schedule_work(&blkiolat->enable_work); 807 } 808 if (oldval && !val) { 809 blkcg_clear_delay(blkg); 810 if (atomic_dec_return(&blkiolat->enable_cnt) == 0) 811 schedule_work(&blkiolat->enable_work); 812 } 813 } 814 815 static void iolatency_clear_scaling(struct blkcg_gq *blkg) 816 { 817 if (blkg->parent) { 818 struct iolatency_grp *iolat = blkg_to_lat(blkg->parent); 819 struct child_latency_info *lat_info; 820 if (!iolat) 821 return; 822 823 lat_info = &iolat->child_lat; 824 spin_lock(&lat_info->lock); 825 atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE); 826 lat_info->last_scale_event = 0; 827 lat_info->scale_grp = NULL; 828 lat_info->scale_lat = 0; 829 spin_unlock(&lat_info->lock); 830 } 831 } 832 833 static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf, 834 size_t nbytes, loff_t off) 835 { 836 struct blkcg *blkcg = css_to_blkcg(of_css(of)); 837 struct blkcg_gq *blkg; 838 struct blkg_conf_ctx ctx; 839 struct iolatency_grp *iolat; 840 char *p, *tok; 841 u64 lat_val = 0; 842 u64 oldval; 843 int ret; 844 845 ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx); 846 if (ret) 847 return ret; 848 849 iolat = blkg_to_lat(ctx.blkg); 850 p = ctx.body; 851 852 ret = -EINVAL; 853 while ((tok = strsep(&p, " "))) { 854 char key[16]; 855 char val[21]; /* 18446744073709551616 */ 856 857 if (sscanf(tok, "%15[^=]=%20s", key, val) != 2) 858 goto out; 859 860 if (!strcmp(key, "target")) { 861 u64 v; 862 863 if (!strcmp(val, "max")) 864 lat_val = 0; 865 else if (sscanf(val, "%llu", &v) == 1) 866 lat_val = v * NSEC_PER_USEC; 867 else 868 goto out; 869 } else { 870 goto out; 871 } 872 } 873 874 /* Walk up the tree to see if our new val is lower than it should be. */ 875 blkg = ctx.blkg; 876 oldval = iolat->min_lat_nsec; 877 878 iolatency_set_min_lat_nsec(blkg, lat_val); 879 if (oldval != iolat->min_lat_nsec) 880 iolatency_clear_scaling(blkg); 881 ret = 0; 882 out: 883 blkg_conf_finish(&ctx); 884 return ret ?: nbytes; 885 } 886 887 static u64 iolatency_prfill_limit(struct seq_file *sf, 888 struct blkg_policy_data *pd, int off) 889 { 890 struct iolatency_grp *iolat = pd_to_lat(pd); 891 const char *dname = blkg_dev_name(pd->blkg); 892 893 if (!dname || !iolat->min_lat_nsec) 894 return 0; 895 seq_printf(sf, "%s target=%llu\n", 896 dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC)); 897 return 0; 898 } 899 900 static int iolatency_print_limit(struct seq_file *sf, void *v) 901 { 902 blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), 903 iolatency_prfill_limit, 904 &blkcg_policy_iolatency, seq_cft(sf)->private, false); 905 return 0; 906 } 907 908 static void iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s) 909 { 910 struct latency_stat stat; 911 int cpu; 912 913 latency_stat_init(iolat, &stat); 914 preempt_disable(); 915 for_each_online_cpu(cpu) { 916 struct latency_stat *s; 917 s = per_cpu_ptr(iolat->stats, cpu); 918 latency_stat_sum(iolat, &stat, s); 919 } 920 preempt_enable(); 921 922 if (iolat->max_depth == UINT_MAX) 923 seq_printf(s, " missed=%llu total=%llu depth=max", 924 (unsigned long long)stat.ps.missed, 925 (unsigned long long)stat.ps.total); 926 else 927 seq_printf(s, " missed=%llu total=%llu depth=%u", 928 (unsigned long long)stat.ps.missed, 929 (unsigned long long)stat.ps.total, 930 iolat->max_depth); 931 } 932 933 static void iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s) 934 { 935 struct iolatency_grp *iolat = pd_to_lat(pd); 936 unsigned long long avg_lat; 937 unsigned long long cur_win; 938 939 if (!blkcg_debug_stats) 940 return; 941 942 if (iolat->ssd) 943 return iolatency_ssd_stat(iolat, s); 944 945 avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC); 946 cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC); 947 if (iolat->max_depth == UINT_MAX) 948 seq_printf(s, " depth=max avg_lat=%llu win=%llu", 949 avg_lat, cur_win); 950 else 951 seq_printf(s, " depth=%u avg_lat=%llu win=%llu", 952 iolat->max_depth, avg_lat, cur_win); 953 } 954 955 static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp, 956 struct request_queue *q, 957 struct blkcg *blkcg) 958 { 959 struct iolatency_grp *iolat; 960 961 iolat = kzalloc_node(sizeof(*iolat), gfp, q->node); 962 if (!iolat) 963 return NULL; 964 iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat), 965 __alignof__(struct latency_stat), gfp); 966 if (!iolat->stats) { 967 kfree(iolat); 968 return NULL; 969 } 970 return &iolat->pd; 971 } 972 973 static void iolatency_pd_init(struct blkg_policy_data *pd) 974 { 975 struct iolatency_grp *iolat = pd_to_lat(pd); 976 struct blkcg_gq *blkg = lat_to_blkg(iolat); 977 struct rq_qos *rqos = blkcg_rq_qos(blkg->q); 978 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 979 u64 now = ktime_to_ns(ktime_get()); 980 int cpu; 981 982 if (blk_queue_nonrot(blkg->q)) 983 iolat->ssd = true; 984 else 985 iolat->ssd = false; 986 987 for_each_possible_cpu(cpu) { 988 struct latency_stat *stat; 989 stat = per_cpu_ptr(iolat->stats, cpu); 990 latency_stat_init(iolat, stat); 991 } 992 993 latency_stat_init(iolat, &iolat->cur_stat); 994 rq_wait_init(&iolat->rq_wait); 995 spin_lock_init(&iolat->child_lat.lock); 996 iolat->max_depth = UINT_MAX; 997 iolat->blkiolat = blkiolat; 998 iolat->cur_win_nsec = 100 * NSEC_PER_MSEC; 999 atomic64_set(&iolat->window_start, now); 1000 1001 /* 1002 * We init things in list order, so the pd for the parent may not be 1003 * init'ed yet for whatever reason. 1004 */ 1005 if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) { 1006 struct iolatency_grp *parent = blkg_to_lat(blkg->parent); 1007 atomic_set(&iolat->scale_cookie, 1008 atomic_read(&parent->child_lat.scale_cookie)); 1009 } else { 1010 atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE); 1011 } 1012 1013 atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE); 1014 } 1015 1016 static void iolatency_pd_offline(struct blkg_policy_data *pd) 1017 { 1018 struct iolatency_grp *iolat = pd_to_lat(pd); 1019 struct blkcg_gq *blkg = lat_to_blkg(iolat); 1020 1021 iolatency_set_min_lat_nsec(blkg, 0); 1022 iolatency_clear_scaling(blkg); 1023 } 1024 1025 static void iolatency_pd_free(struct blkg_policy_data *pd) 1026 { 1027 struct iolatency_grp *iolat = pd_to_lat(pd); 1028 free_percpu(iolat->stats); 1029 kfree(iolat); 1030 } 1031 1032 static struct cftype iolatency_files[] = { 1033 { 1034 .name = "latency", 1035 .flags = CFTYPE_NOT_ON_ROOT, 1036 .seq_show = iolatency_print_limit, 1037 .write = iolatency_set_limit, 1038 }, 1039 {} 1040 }; 1041 1042 static struct blkcg_policy blkcg_policy_iolatency = { 1043 .dfl_cftypes = iolatency_files, 1044 .pd_alloc_fn = iolatency_pd_alloc, 1045 .pd_init_fn = iolatency_pd_init, 1046 .pd_offline_fn = iolatency_pd_offline, 1047 .pd_free_fn = iolatency_pd_free, 1048 .pd_stat_fn = iolatency_pd_stat, 1049 }; 1050 1051 static int __init iolatency_init(void) 1052 { 1053 return blkcg_policy_register(&blkcg_policy_iolatency); 1054 } 1055 1056 static void __exit iolatency_exit(void) 1057 { 1058 blkcg_policy_unregister(&blkcg_policy_iolatency); 1059 } 1060 1061 module_init(iolatency_init); 1062 module_exit(iolatency_exit); 1063