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 struct rq_depth rq_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->rq_depth.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/subtract 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. 370 */ 371 static void scale_change(struct iolatency_grp *iolat, bool up) 372 { 373 unsigned long qd = iolat->blkiolat->rqos.q->nr_requests; 374 unsigned long scale = scale_amount(qd, up); 375 unsigned long old = iolat->rq_depth.max_depth; 376 377 if (old > qd) 378 old = qd; 379 380 if (up) { 381 if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat))) 382 return; 383 384 if (old < qd) { 385 old += scale; 386 old = min(old, qd); 387 iolat->rq_depth.max_depth = old; 388 wake_up_all(&iolat->rq_wait.wait); 389 } 390 } else { 391 old >>= 1; 392 iolat->rq_depth.max_depth = max(old, 1UL); 393 } 394 } 395 396 /* Check our parent and see if the scale cookie has changed. */ 397 static void check_scale_change(struct iolatency_grp *iolat) 398 { 399 struct iolatency_grp *parent; 400 struct child_latency_info *lat_info; 401 unsigned int cur_cookie; 402 unsigned int our_cookie = atomic_read(&iolat->scale_cookie); 403 u64 scale_lat; 404 int direction = 0; 405 406 if (lat_to_blkg(iolat)->parent == NULL) 407 return; 408 409 parent = blkg_to_lat(lat_to_blkg(iolat)->parent); 410 if (!parent) 411 return; 412 413 lat_info = &parent->child_lat; 414 cur_cookie = atomic_read(&lat_info->scale_cookie); 415 scale_lat = READ_ONCE(lat_info->scale_lat); 416 417 if (cur_cookie < our_cookie) 418 direction = -1; 419 else if (cur_cookie > our_cookie) 420 direction = 1; 421 else 422 return; 423 424 if (!atomic_try_cmpxchg(&iolat->scale_cookie, &our_cookie, cur_cookie)) { 425 /* Somebody beat us to the punch, just bail. */ 426 return; 427 } 428 429 if (direction < 0 && iolat->min_lat_nsec) { 430 u64 samples_thresh; 431 432 if (!scale_lat || iolat->min_lat_nsec <= scale_lat) 433 return; 434 435 /* 436 * Sometimes high priority groups are their own worst enemy, so 437 * instead of taking it out on some poor other group that did 5% 438 * or less of the IO's for the last summation just skip this 439 * scale down event. 440 */ 441 samples_thresh = lat_info->nr_samples * 5; 442 samples_thresh = max(1ULL, div64_u64(samples_thresh, 100)); 443 if (iolat->nr_samples <= samples_thresh) 444 return; 445 } 446 447 /* We're as low as we can go. */ 448 if (iolat->rq_depth.max_depth == 1 && direction < 0) { 449 blkcg_use_delay(lat_to_blkg(iolat)); 450 return; 451 } 452 453 /* We're back to the default cookie, unthrottle all the things. */ 454 if (cur_cookie == DEFAULT_SCALE_COOKIE) { 455 blkcg_clear_delay(lat_to_blkg(iolat)); 456 iolat->rq_depth.max_depth = UINT_MAX; 457 wake_up_all(&iolat->rq_wait.wait); 458 return; 459 } 460 461 scale_change(iolat, direction > 0); 462 } 463 464 static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) 465 { 466 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 467 struct blkcg_gq *blkg = bio->bi_blkg; 468 bool issue_as_root = bio_issue_as_root_blkg(bio); 469 470 if (!blkiolat->enabled) 471 return; 472 473 while (blkg && blkg->parent) { 474 struct iolatency_grp *iolat = blkg_to_lat(blkg); 475 if (!iolat) { 476 blkg = blkg->parent; 477 continue; 478 } 479 480 check_scale_change(iolat); 481 __blkcg_iolatency_throttle(rqos, iolat, issue_as_root, 482 (bio->bi_opf & REQ_SWAP) == REQ_SWAP); 483 blkg = blkg->parent; 484 } 485 if (!timer_pending(&blkiolat->timer)) 486 mod_timer(&blkiolat->timer, jiffies + HZ); 487 } 488 489 static void iolatency_record_time(struct iolatency_grp *iolat, 490 struct bio_issue *issue, u64 now, 491 bool issue_as_root) 492 { 493 u64 start = bio_issue_time(issue); 494 u64 req_time; 495 496 /* 497 * Have to do this so we are truncated to the correct time that our 498 * issue is truncated to. 499 */ 500 now = __bio_issue_time(now); 501 502 if (now <= start) 503 return; 504 505 req_time = now - start; 506 507 /* 508 * We don't want to count issue_as_root bio's in the cgroups latency 509 * statistics as it could skew the numbers downwards. 510 */ 511 if (unlikely(issue_as_root && iolat->rq_depth.max_depth != UINT_MAX)) { 512 u64 sub = iolat->min_lat_nsec; 513 if (req_time < sub) 514 blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time); 515 return; 516 } 517 518 latency_stat_record_time(iolat, req_time); 519 } 520 521 #define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC) 522 #define BLKIOLATENCY_MIN_GOOD_SAMPLES 5 523 524 static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now) 525 { 526 struct blkcg_gq *blkg = lat_to_blkg(iolat); 527 struct iolatency_grp *parent; 528 struct child_latency_info *lat_info; 529 struct latency_stat stat; 530 unsigned long flags; 531 int cpu; 532 533 latency_stat_init(iolat, &stat); 534 preempt_disable(); 535 for_each_online_cpu(cpu) { 536 struct latency_stat *s; 537 s = per_cpu_ptr(iolat->stats, cpu); 538 latency_stat_sum(iolat, &stat, s); 539 latency_stat_init(iolat, s); 540 } 541 preempt_enable(); 542 543 parent = blkg_to_lat(blkg->parent); 544 if (!parent) 545 return; 546 547 lat_info = &parent->child_lat; 548 549 iolat_update_total_lat_avg(iolat, &stat); 550 551 /* Everything is ok and we don't need to adjust the scale. */ 552 if (latency_sum_ok(iolat, &stat) && 553 atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE) 554 return; 555 556 /* Somebody beat us to the punch, just bail. */ 557 spin_lock_irqsave(&lat_info->lock, flags); 558 559 latency_stat_sum(iolat, &iolat->cur_stat, &stat); 560 lat_info->nr_samples -= iolat->nr_samples; 561 lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat); 562 iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat); 563 564 if ((lat_info->last_scale_event >= now || 565 now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME)) 566 goto out; 567 568 if (latency_sum_ok(iolat, &iolat->cur_stat) && 569 latency_sum_ok(iolat, &stat)) { 570 if (latency_stat_samples(iolat, &iolat->cur_stat) < 571 BLKIOLATENCY_MIN_GOOD_SAMPLES) 572 goto out; 573 if (lat_info->scale_grp == iolat) { 574 lat_info->last_scale_event = now; 575 scale_cookie_change(iolat->blkiolat, lat_info, true); 576 } 577 } else if (lat_info->scale_lat == 0 || 578 lat_info->scale_lat >= iolat->min_lat_nsec) { 579 lat_info->last_scale_event = now; 580 if (!lat_info->scale_grp || 581 lat_info->scale_lat > iolat->min_lat_nsec) { 582 WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec); 583 lat_info->scale_grp = iolat; 584 } 585 scale_cookie_change(iolat->blkiolat, lat_info, false); 586 } 587 latency_stat_init(iolat, &iolat->cur_stat); 588 out: 589 spin_unlock_irqrestore(&lat_info->lock, flags); 590 } 591 592 static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) 593 { 594 struct blkcg_gq *blkg; 595 struct rq_wait *rqw; 596 struct iolatency_grp *iolat; 597 u64 window_start; 598 u64 now; 599 bool issue_as_root = bio_issue_as_root_blkg(bio); 600 int inflight = 0; 601 602 blkg = bio->bi_blkg; 603 if (!blkg || !bio_flagged(bio, BIO_QOS_THROTTLED)) 604 return; 605 606 iolat = blkg_to_lat(bio->bi_blkg); 607 if (!iolat) 608 return; 609 610 if (!iolat->blkiolat->enabled) 611 return; 612 613 now = ktime_to_ns(ktime_get()); 614 while (blkg && blkg->parent) { 615 iolat = blkg_to_lat(blkg); 616 if (!iolat) { 617 blkg = blkg->parent; 618 continue; 619 } 620 rqw = &iolat->rq_wait; 621 622 inflight = atomic_dec_return(&rqw->inflight); 623 WARN_ON_ONCE(inflight < 0); 624 /* 625 * If bi_status is BLK_STS_AGAIN, the bio wasn't actually 626 * submitted, so do not account for it. 627 */ 628 if (iolat->min_lat_nsec && bio->bi_status != BLK_STS_AGAIN) { 629 iolatency_record_time(iolat, &bio->bi_issue, now, 630 issue_as_root); 631 window_start = atomic64_read(&iolat->window_start); 632 if (now > window_start && 633 (now - window_start) >= iolat->cur_win_nsec) { 634 if (atomic64_try_cmpxchg(&iolat->window_start, 635 &window_start, now)) 636 iolatency_check_latencies(iolat, now); 637 } 638 } 639 wake_up(&rqw->wait); 640 blkg = blkg->parent; 641 } 642 } 643 644 static void blkcg_iolatency_exit(struct rq_qos *rqos) 645 { 646 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 647 648 del_timer_sync(&blkiolat->timer); 649 flush_work(&blkiolat->enable_work); 650 blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency); 651 kfree(blkiolat); 652 } 653 654 static struct rq_qos_ops blkcg_iolatency_ops = { 655 .throttle = blkcg_iolatency_throttle, 656 .done_bio = blkcg_iolatency_done_bio, 657 .exit = blkcg_iolatency_exit, 658 }; 659 660 static void blkiolatency_timer_fn(struct timer_list *t) 661 { 662 struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer); 663 struct blkcg_gq *blkg; 664 struct cgroup_subsys_state *pos_css; 665 u64 now = ktime_to_ns(ktime_get()); 666 667 rcu_read_lock(); 668 blkg_for_each_descendant_pre(blkg, pos_css, 669 blkiolat->rqos.q->root_blkg) { 670 struct iolatency_grp *iolat; 671 struct child_latency_info *lat_info; 672 unsigned long flags; 673 u64 cookie; 674 675 /* 676 * We could be exiting, don't access the pd unless we have a 677 * ref on the blkg. 678 */ 679 if (!blkg_tryget(blkg)) 680 continue; 681 682 iolat = blkg_to_lat(blkg); 683 if (!iolat) 684 goto next; 685 686 lat_info = &iolat->child_lat; 687 cookie = atomic_read(&lat_info->scale_cookie); 688 689 if (cookie >= DEFAULT_SCALE_COOKIE) 690 goto next; 691 692 spin_lock_irqsave(&lat_info->lock, flags); 693 if (lat_info->last_scale_event >= now) 694 goto next_lock; 695 696 /* 697 * We scaled down but don't have a scale_grp, scale up and carry 698 * on. 699 */ 700 if (lat_info->scale_grp == NULL) { 701 scale_cookie_change(iolat->blkiolat, lat_info, true); 702 goto next_lock; 703 } 704 705 /* 706 * It's been 5 seconds since our last scale event, clear the 707 * scale grp in case the group that needed the scale down isn't 708 * doing any IO currently. 709 */ 710 if (now - lat_info->last_scale_event >= 711 ((u64)NSEC_PER_SEC * 5)) 712 lat_info->scale_grp = NULL; 713 next_lock: 714 spin_unlock_irqrestore(&lat_info->lock, flags); 715 next: 716 blkg_put(blkg); 717 } 718 rcu_read_unlock(); 719 } 720 721 /** 722 * blkiolatency_enable_work_fn - Enable or disable iolatency on the device 723 * @work: enable_work of the blk_iolatency of interest 724 * 725 * iolatency needs to keep track of the number of in-flight IOs per cgroup. This 726 * is relatively expensive as it involves walking up the hierarchy twice for 727 * every IO. Thus, if iolatency is not enabled in any cgroup for the device, we 728 * want to disable the in-flight tracking. 729 * 730 * We have to make sure that the counting is balanced - we don't want to leak 731 * the in-flight counts by disabling accounting in the completion path while IOs 732 * are in flight. This is achieved by ensuring that no IO is in flight by 733 * freezing the queue while flipping ->enabled. As this requires a sleepable 734 * context, ->enabled flipping is punted to this work function. 735 */ 736 static void blkiolatency_enable_work_fn(struct work_struct *work) 737 { 738 struct blk_iolatency *blkiolat = container_of(work, struct blk_iolatency, 739 enable_work); 740 bool enabled; 741 742 /* 743 * There can only be one instance of this function running for @blkiolat 744 * and it's guaranteed to be executed at least once after the latest 745 * ->enabled_cnt modification. Acting on the latest ->enable_cnt is 746 * sufficient. 747 * 748 * Also, we know @blkiolat is safe to access as ->enable_work is flushed 749 * in blkcg_iolatency_exit(). 750 */ 751 enabled = atomic_read(&blkiolat->enable_cnt); 752 if (enabled != blkiolat->enabled) { 753 blk_mq_freeze_queue(blkiolat->rqos.q); 754 blkiolat->enabled = enabled; 755 blk_mq_unfreeze_queue(blkiolat->rqos.q); 756 } 757 } 758 759 int blk_iolatency_init(struct gendisk *disk) 760 { 761 struct request_queue *q = disk->queue; 762 struct blk_iolatency *blkiolat; 763 struct rq_qos *rqos; 764 int ret; 765 766 blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL); 767 if (!blkiolat) 768 return -ENOMEM; 769 770 rqos = &blkiolat->rqos; 771 rqos->id = RQ_QOS_LATENCY; 772 rqos->ops = &blkcg_iolatency_ops; 773 rqos->q = q; 774 775 ret = rq_qos_add(q, rqos); 776 if (ret) 777 goto err_free; 778 ret = blkcg_activate_policy(q, &blkcg_policy_iolatency); 779 if (ret) 780 goto err_qos_del; 781 782 timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0); 783 INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn); 784 785 return 0; 786 787 err_qos_del: 788 rq_qos_del(q, rqos); 789 err_free: 790 kfree(blkiolat); 791 return ret; 792 } 793 794 static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) 795 { 796 struct iolatency_grp *iolat = blkg_to_lat(blkg); 797 struct blk_iolatency *blkiolat = iolat->blkiolat; 798 u64 oldval = iolat->min_lat_nsec; 799 800 iolat->min_lat_nsec = val; 801 iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE); 802 iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, 803 BLKIOLATENCY_MAX_WIN_SIZE); 804 805 if (!oldval && val) { 806 if (atomic_inc_return(&blkiolat->enable_cnt) == 1) 807 schedule_work(&blkiolat->enable_work); 808 } 809 if (oldval && !val) { 810 blkcg_clear_delay(blkg); 811 if (atomic_dec_return(&blkiolat->enable_cnt) == 0) 812 schedule_work(&blkiolat->enable_work); 813 } 814 } 815 816 static void iolatency_clear_scaling(struct blkcg_gq *blkg) 817 { 818 if (blkg->parent) { 819 struct iolatency_grp *iolat = blkg_to_lat(blkg->parent); 820 struct child_latency_info *lat_info; 821 if (!iolat) 822 return; 823 824 lat_info = &iolat->child_lat; 825 spin_lock(&lat_info->lock); 826 atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE); 827 lat_info->last_scale_event = 0; 828 lat_info->scale_grp = NULL; 829 lat_info->scale_lat = 0; 830 spin_unlock(&lat_info->lock); 831 } 832 } 833 834 static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf, 835 size_t nbytes, loff_t off) 836 { 837 struct blkcg *blkcg = css_to_blkcg(of_css(of)); 838 struct blkcg_gq *blkg; 839 struct blkg_conf_ctx ctx; 840 struct iolatency_grp *iolat; 841 char *p, *tok; 842 u64 lat_val = 0; 843 u64 oldval; 844 int ret; 845 846 ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx); 847 if (ret) 848 return ret; 849 850 iolat = blkg_to_lat(ctx.blkg); 851 p = ctx.body; 852 853 ret = -EINVAL; 854 while ((tok = strsep(&p, " "))) { 855 char key[16]; 856 char val[21]; /* 18446744073709551616 */ 857 858 if (sscanf(tok, "%15[^=]=%20s", key, val) != 2) 859 goto out; 860 861 if (!strcmp(key, "target")) { 862 u64 v; 863 864 if (!strcmp(val, "max")) 865 lat_val = 0; 866 else if (sscanf(val, "%llu", &v) == 1) 867 lat_val = v * NSEC_PER_USEC; 868 else 869 goto out; 870 } else { 871 goto out; 872 } 873 } 874 875 /* Walk up the tree to see if our new val is lower than it should be. */ 876 blkg = ctx.blkg; 877 oldval = iolat->min_lat_nsec; 878 879 iolatency_set_min_lat_nsec(blkg, lat_val); 880 if (oldval != iolat->min_lat_nsec) 881 iolatency_clear_scaling(blkg); 882 ret = 0; 883 out: 884 blkg_conf_finish(&ctx); 885 return ret ?: nbytes; 886 } 887 888 static u64 iolatency_prfill_limit(struct seq_file *sf, 889 struct blkg_policy_data *pd, int off) 890 { 891 struct iolatency_grp *iolat = pd_to_lat(pd); 892 const char *dname = blkg_dev_name(pd->blkg); 893 894 if (!dname || !iolat->min_lat_nsec) 895 return 0; 896 seq_printf(sf, "%s target=%llu\n", 897 dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC)); 898 return 0; 899 } 900 901 static int iolatency_print_limit(struct seq_file *sf, void *v) 902 { 903 blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), 904 iolatency_prfill_limit, 905 &blkcg_policy_iolatency, seq_cft(sf)->private, false); 906 return 0; 907 } 908 909 static void iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s) 910 { 911 struct latency_stat stat; 912 int cpu; 913 914 latency_stat_init(iolat, &stat); 915 preempt_disable(); 916 for_each_online_cpu(cpu) { 917 struct latency_stat *s; 918 s = per_cpu_ptr(iolat->stats, cpu); 919 latency_stat_sum(iolat, &stat, s); 920 } 921 preempt_enable(); 922 923 if (iolat->rq_depth.max_depth == UINT_MAX) 924 seq_printf(s, " missed=%llu total=%llu depth=max", 925 (unsigned long long)stat.ps.missed, 926 (unsigned long long)stat.ps.total); 927 else 928 seq_printf(s, " missed=%llu total=%llu depth=%u", 929 (unsigned long long)stat.ps.missed, 930 (unsigned long long)stat.ps.total, 931 iolat->rq_depth.max_depth); 932 } 933 934 static void iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s) 935 { 936 struct iolatency_grp *iolat = pd_to_lat(pd); 937 unsigned long long avg_lat; 938 unsigned long long cur_win; 939 940 if (!blkcg_debug_stats) 941 return; 942 943 if (iolat->ssd) 944 return iolatency_ssd_stat(iolat, s); 945 946 avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC); 947 cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC); 948 if (iolat->rq_depth.max_depth == UINT_MAX) 949 seq_printf(s, " depth=max avg_lat=%llu win=%llu", 950 avg_lat, cur_win); 951 else 952 seq_printf(s, " depth=%u avg_lat=%llu win=%llu", 953 iolat->rq_depth.max_depth, avg_lat, cur_win); 954 } 955 956 static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp, 957 struct request_queue *q, 958 struct blkcg *blkcg) 959 { 960 struct iolatency_grp *iolat; 961 962 iolat = kzalloc_node(sizeof(*iolat), gfp, q->node); 963 if (!iolat) 964 return NULL; 965 iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat), 966 __alignof__(struct latency_stat), gfp); 967 if (!iolat->stats) { 968 kfree(iolat); 969 return NULL; 970 } 971 return &iolat->pd; 972 } 973 974 static void iolatency_pd_init(struct blkg_policy_data *pd) 975 { 976 struct iolatency_grp *iolat = pd_to_lat(pd); 977 struct blkcg_gq *blkg = lat_to_blkg(iolat); 978 struct rq_qos *rqos = blkcg_rq_qos(blkg->q); 979 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 980 u64 now = ktime_to_ns(ktime_get()); 981 int cpu; 982 983 if (blk_queue_nonrot(blkg->q)) 984 iolat->ssd = true; 985 else 986 iolat->ssd = false; 987 988 for_each_possible_cpu(cpu) { 989 struct latency_stat *stat; 990 stat = per_cpu_ptr(iolat->stats, cpu); 991 latency_stat_init(iolat, stat); 992 } 993 994 latency_stat_init(iolat, &iolat->cur_stat); 995 rq_wait_init(&iolat->rq_wait); 996 spin_lock_init(&iolat->child_lat.lock); 997 iolat->rq_depth.queue_depth = blkg->q->nr_requests; 998 iolat->rq_depth.max_depth = UINT_MAX; 999 iolat->rq_depth.default_depth = iolat->rq_depth.queue_depth; 1000 iolat->blkiolat = blkiolat; 1001 iolat->cur_win_nsec = 100 * NSEC_PER_MSEC; 1002 atomic64_set(&iolat->window_start, now); 1003 1004 /* 1005 * We init things in list order, so the pd for the parent may not be 1006 * init'ed yet for whatever reason. 1007 */ 1008 if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) { 1009 struct iolatency_grp *parent = blkg_to_lat(blkg->parent); 1010 atomic_set(&iolat->scale_cookie, 1011 atomic_read(&parent->child_lat.scale_cookie)); 1012 } else { 1013 atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE); 1014 } 1015 1016 atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE); 1017 } 1018 1019 static void iolatency_pd_offline(struct blkg_policy_data *pd) 1020 { 1021 struct iolatency_grp *iolat = pd_to_lat(pd); 1022 struct blkcg_gq *blkg = lat_to_blkg(iolat); 1023 1024 iolatency_set_min_lat_nsec(blkg, 0); 1025 iolatency_clear_scaling(blkg); 1026 } 1027 1028 static void iolatency_pd_free(struct blkg_policy_data *pd) 1029 { 1030 struct iolatency_grp *iolat = pd_to_lat(pd); 1031 free_percpu(iolat->stats); 1032 kfree(iolat); 1033 } 1034 1035 static struct cftype iolatency_files[] = { 1036 { 1037 .name = "latency", 1038 .flags = CFTYPE_NOT_ON_ROOT, 1039 .seq_show = iolatency_print_limit, 1040 .write = iolatency_set_limit, 1041 }, 1042 {} 1043 }; 1044 1045 static struct blkcg_policy blkcg_policy_iolatency = { 1046 .dfl_cftypes = iolatency_files, 1047 .pd_alloc_fn = iolatency_pd_alloc, 1048 .pd_init_fn = iolatency_pd_init, 1049 .pd_offline_fn = iolatency_pd_offline, 1050 .pd_free_fn = iolatency_pd_free, 1051 .pd_stat_fn = iolatency_pd_stat, 1052 }; 1053 1054 static int __init iolatency_init(void) 1055 { 1056 return blkcg_policy_register(&blkcg_policy_iolatency); 1057 } 1058 1059 static void __exit iolatency_exit(void) 1060 { 1061 blkcg_policy_unregister(&blkcg_policy_iolatency); 1062 } 1063 1064 module_init(iolatency_init); 1065 module_exit(iolatency_exit); 1066