1 /* 2 * Block rq-qos base io controller 3 * 4 * This works similar to wbt with a few exceptions 5 * 6 * - It's bio based, so the latency covers the whole block layer in addition to 7 * the actual io. 8 * - We will throttle all IO that comes in here if we need to. 9 * - We use the mean latency over the 100ms window. This is because writes can 10 * be particularly fast, which could give us a false sense of the impact of 11 * other workloads on our protected workload. 12 * - By default there's no throttling, we set the queue_depth to UINT_MAX so 13 * that we can have as many outstanding bio's as we're allowed to. Only at 14 * throttle time do we pay attention to the actual queue depth. 15 * 16 * The hierarchy works like the cpu controller does, we track the latency at 17 * every configured node, and each configured node has it's own independent 18 * queue depth. This means that we only care about our latency targets at the 19 * peer level. Some group at the bottom of the hierarchy isn't going to affect 20 * a group at the end of some other path if we're only configred at leaf level. 21 * 22 * Consider the following 23 * 24 * root blkg 25 * / \ 26 * fast (target=5ms) slow (target=10ms) 27 * / \ / \ 28 * a b normal(15ms) unloved 29 * 30 * "a" and "b" have no target, but their combined io under "fast" cannot exceed 31 * an average latency of 5ms. If it does then we will throttle the "slow" 32 * group. In the case of "normal", if it exceeds its 15ms target, we will 33 * throttle "unloved", but nobody else. 34 * 35 * In this example "fast", "slow", and "normal" will be the only groups actually 36 * accounting their io latencies. We have to walk up the heirarchy to the root 37 * on every submit and complete so we can do the appropriate stat recording and 38 * adjust the queue depth of ourselves if needed. 39 * 40 * There are 2 ways we throttle IO. 41 * 42 * 1) Queue depth throttling. As we throttle down we will adjust the maximum 43 * number of IO's we're allowed to have in flight. This starts at (u64)-1 down 44 * to 1. If the group is only ever submitting IO for itself then this is the 45 * only way we throttle. 46 * 47 * 2) Induced delay throttling. This is for the case that a group is generating 48 * IO that has to be issued by the root cg to avoid priority inversion. So think 49 * REQ_META or REQ_SWAP. If we are already at qd == 1 and we're getting a lot 50 * of work done for us on behalf of the root cg and are being asked to scale 51 * down more then we induce a latency at userspace return. We accumulate the 52 * total amount of time we need to be punished by doing 53 * 54 * total_time += min_lat_nsec - actual_io_completion 55 * 56 * and then at throttle time will do 57 * 58 * throttle_time = min(total_time, NSEC_PER_SEC) 59 * 60 * This induced delay will throttle back the activity that is generating the 61 * root cg issued io's, wethere that's some metadata intensive operation or the 62 * group is using so much memory that it is pushing us into swap. 63 * 64 * Copyright (C) 2018 Josef Bacik 65 */ 66 #include <linux/kernel.h> 67 #include <linux/blk_types.h> 68 #include <linux/backing-dev.h> 69 #include <linux/module.h> 70 #include <linux/timer.h> 71 #include <linux/memcontrol.h> 72 #include <linux/sched/loadavg.h> 73 #include <linux/sched/signal.h> 74 #include <trace/events/block.h> 75 #include <linux/blk-mq.h> 76 #include "blk-rq-qos.h" 77 #include "blk-stat.h" 78 79 #define DEFAULT_SCALE_COOKIE 1000000U 80 81 static struct blkcg_policy blkcg_policy_iolatency; 82 struct iolatency_grp; 83 84 struct blk_iolatency { 85 struct rq_qos rqos; 86 struct timer_list timer; 87 atomic_t enabled; 88 }; 89 90 static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos) 91 { 92 return container_of(rqos, struct blk_iolatency, rqos); 93 } 94 95 static inline bool blk_iolatency_enabled(struct blk_iolatency *blkiolat) 96 { 97 return atomic_read(&blkiolat->enabled) > 0; 98 } 99 100 struct child_latency_info { 101 spinlock_t lock; 102 103 /* Last time we adjusted the scale of everybody. */ 104 u64 last_scale_event; 105 106 /* The latency that we missed. */ 107 u64 scale_lat; 108 109 /* Total io's from all of our children for the last summation. */ 110 u64 nr_samples; 111 112 /* The guy who actually changed the latency numbers. */ 113 struct iolatency_grp *scale_grp; 114 115 /* Cookie to tell if we need to scale up or down. */ 116 atomic_t scale_cookie; 117 }; 118 119 struct percentile_stats { 120 u64 total; 121 u64 missed; 122 }; 123 124 struct latency_stat { 125 union { 126 struct percentile_stats ps; 127 struct blk_rq_stat rqs; 128 }; 129 }; 130 131 struct iolatency_grp { 132 struct blkg_policy_data pd; 133 struct latency_stat __percpu *stats; 134 struct latency_stat cur_stat; 135 struct blk_iolatency *blkiolat; 136 struct rq_depth rq_depth; 137 struct rq_wait rq_wait; 138 atomic64_t window_start; 139 atomic_t scale_cookie; 140 u64 min_lat_nsec; 141 u64 cur_win_nsec; 142 143 /* total running average of our io latency. */ 144 u64 lat_avg; 145 146 /* Our current number of IO's for the last summation. */ 147 u64 nr_samples; 148 149 bool ssd; 150 struct child_latency_info child_lat; 151 }; 152 153 #define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC) 154 #define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC 155 /* 156 * These are the constants used to fake the fixed-point moving average 157 * calculation just like load average. The call to calc_load() folds 158 * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg. The sampling 159 * window size is bucketed to try to approximately calculate average 160 * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows 161 * elapse immediately. Note, windows only elapse with IO activity. Idle 162 * periods extend the most recent window. 163 */ 164 #define BLKIOLATENCY_NR_EXP_FACTORS 5 165 #define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \ 166 (BLKIOLATENCY_NR_EXP_FACTORS - 1)) 167 static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = { 168 2045, // exp(1/600) - 600 samples 169 2039, // exp(1/240) - 240 samples 170 2031, // exp(1/120) - 120 samples 171 2023, // exp(1/80) - 80 samples 172 2014, // exp(1/60) - 60 samples 173 }; 174 175 static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd) 176 { 177 return pd ? container_of(pd, struct iolatency_grp, pd) : NULL; 178 } 179 180 static inline struct iolatency_grp *blkg_to_lat(struct blkcg_gq *blkg) 181 { 182 return pd_to_lat(blkg_to_pd(blkg, &blkcg_policy_iolatency)); 183 } 184 185 static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat) 186 { 187 return pd_to_blkg(&iolat->pd); 188 } 189 190 static inline void latency_stat_init(struct iolatency_grp *iolat, 191 struct latency_stat *stat) 192 { 193 if (iolat->ssd) { 194 stat->ps.total = 0; 195 stat->ps.missed = 0; 196 } else 197 blk_rq_stat_init(&stat->rqs); 198 } 199 200 static inline void latency_stat_sum(struct iolatency_grp *iolat, 201 struct latency_stat *sum, 202 struct latency_stat *stat) 203 { 204 if (iolat->ssd) { 205 sum->ps.total += stat->ps.total; 206 sum->ps.missed += stat->ps.missed; 207 } else 208 blk_rq_stat_sum(&sum->rqs, &stat->rqs); 209 } 210 211 static inline void latency_stat_record_time(struct iolatency_grp *iolat, 212 u64 req_time) 213 { 214 struct latency_stat *stat = get_cpu_ptr(iolat->stats); 215 if (iolat->ssd) { 216 if (req_time >= iolat->min_lat_nsec) 217 stat->ps.missed++; 218 stat->ps.total++; 219 } else 220 blk_rq_stat_add(&stat->rqs, req_time); 221 put_cpu_ptr(stat); 222 } 223 224 static inline bool latency_sum_ok(struct iolatency_grp *iolat, 225 struct latency_stat *stat) 226 { 227 if (iolat->ssd) { 228 u64 thresh = div64_u64(stat->ps.total, 10); 229 thresh = max(thresh, 1ULL); 230 return stat->ps.missed < thresh; 231 } 232 return stat->rqs.mean <= iolat->min_lat_nsec; 233 } 234 235 static inline u64 latency_stat_samples(struct iolatency_grp *iolat, 236 struct latency_stat *stat) 237 { 238 if (iolat->ssd) 239 return stat->ps.total; 240 return stat->rqs.nr_samples; 241 } 242 243 static inline void iolat_update_total_lat_avg(struct iolatency_grp *iolat, 244 struct latency_stat *stat) 245 { 246 int exp_idx; 247 248 if (iolat->ssd) 249 return; 250 251 /* 252 * calc_load() takes in a number stored in fixed point representation. 253 * Because we are using this for IO time in ns, the values stored 254 * are significantly larger than the FIXED_1 denominator (2048). 255 * Therefore, rounding errors in the calculation are negligible and 256 * can be ignored. 257 */ 258 exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1, 259 div64_u64(iolat->cur_win_nsec, 260 BLKIOLATENCY_EXP_BUCKET_SIZE)); 261 iolat->lat_avg = calc_load(iolat->lat_avg, 262 iolatency_exp_factors[exp_idx], 263 stat->rqs.mean); 264 } 265 266 static void iolat_cleanup_cb(struct rq_wait *rqw, void *private_data) 267 { 268 atomic_dec(&rqw->inflight); 269 wake_up(&rqw->wait); 270 } 271 272 static bool iolat_acquire_inflight(struct rq_wait *rqw, void *private_data) 273 { 274 struct iolatency_grp *iolat = private_data; 275 return rq_wait_inc_below(rqw, iolat->rq_depth.max_depth); 276 } 277 278 static void __blkcg_iolatency_throttle(struct rq_qos *rqos, 279 struct iolatency_grp *iolat, 280 bool issue_as_root, 281 bool use_memdelay) 282 { 283 struct rq_wait *rqw = &iolat->rq_wait; 284 unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay); 285 286 if (use_delay) 287 blkcg_schedule_throttle(rqos->q, use_memdelay); 288 289 /* 290 * To avoid priority inversions we want to just take a slot if we are 291 * issuing as root. If we're being killed off there's no point in 292 * delaying things, we may have been killed by OOM so throttling may 293 * make recovery take even longer, so just let the IO's through so the 294 * task can go away. 295 */ 296 if (issue_as_root || fatal_signal_pending(current)) { 297 atomic_inc(&rqw->inflight); 298 return; 299 } 300 301 rq_qos_wait(rqw, iolat, iolat_acquire_inflight, iolat_cleanup_cb); 302 } 303 304 #define SCALE_DOWN_FACTOR 2 305 #define SCALE_UP_FACTOR 4 306 307 static inline unsigned long scale_amount(unsigned long qd, bool up) 308 { 309 return max(up ? qd >> SCALE_UP_FACTOR : qd >> SCALE_DOWN_FACTOR, 1UL); 310 } 311 312 /* 313 * We scale the qd down faster than we scale up, so we need to use this helper 314 * to adjust the scale_cookie accordingly so we don't prematurely get 315 * scale_cookie at DEFAULT_SCALE_COOKIE and unthrottle too much. 316 * 317 * Each group has their own local copy of the last scale cookie they saw, so if 318 * the global scale cookie goes up or down they know which way they need to go 319 * based on their last knowledge of it. 320 */ 321 static void scale_cookie_change(struct blk_iolatency *blkiolat, 322 struct child_latency_info *lat_info, 323 bool up) 324 { 325 unsigned long qd = blkiolat->rqos.q->nr_requests; 326 unsigned long scale = scale_amount(qd, up); 327 unsigned long old = atomic_read(&lat_info->scale_cookie); 328 unsigned long max_scale = qd << 1; 329 unsigned long diff = 0; 330 331 if (old < DEFAULT_SCALE_COOKIE) 332 diff = DEFAULT_SCALE_COOKIE - old; 333 334 if (up) { 335 if (scale + old > DEFAULT_SCALE_COOKIE) 336 atomic_set(&lat_info->scale_cookie, 337 DEFAULT_SCALE_COOKIE); 338 else if (diff > qd) 339 atomic_inc(&lat_info->scale_cookie); 340 else 341 atomic_add(scale, &lat_info->scale_cookie); 342 } else { 343 /* 344 * We don't want to dig a hole so deep that it takes us hours to 345 * dig out of it. Just enough that we don't throttle/unthrottle 346 * with jagged workloads but can still unthrottle once pressure 347 * has sufficiently dissipated. 348 */ 349 if (diff > qd) { 350 if (diff < max_scale) 351 atomic_dec(&lat_info->scale_cookie); 352 } else { 353 atomic_sub(scale, &lat_info->scale_cookie); 354 } 355 } 356 } 357 358 /* 359 * Change the queue depth of the iolatency_grp. We add/subtract 1/16th of the 360 * queue depth at a time so we don't get wild swings and hopefully dial in to 361 * fairer distribution of the overall queue depth. 362 */ 363 static void scale_change(struct iolatency_grp *iolat, bool up) 364 { 365 unsigned long qd = iolat->blkiolat->rqos.q->nr_requests; 366 unsigned long scale = scale_amount(qd, up); 367 unsigned long old = iolat->rq_depth.max_depth; 368 369 if (old > qd) 370 old = qd; 371 372 if (up) { 373 if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat))) 374 return; 375 376 if (old < qd) { 377 old += scale; 378 old = min(old, qd); 379 iolat->rq_depth.max_depth = old; 380 wake_up_all(&iolat->rq_wait.wait); 381 } 382 } else { 383 old >>= 1; 384 iolat->rq_depth.max_depth = max(old, 1UL); 385 } 386 } 387 388 /* Check our parent and see if the scale cookie has changed. */ 389 static void check_scale_change(struct iolatency_grp *iolat) 390 { 391 struct iolatency_grp *parent; 392 struct child_latency_info *lat_info; 393 unsigned int cur_cookie; 394 unsigned int our_cookie = atomic_read(&iolat->scale_cookie); 395 u64 scale_lat; 396 unsigned int old; 397 int direction = 0; 398 399 if (lat_to_blkg(iolat)->parent == NULL) 400 return; 401 402 parent = blkg_to_lat(lat_to_blkg(iolat)->parent); 403 if (!parent) 404 return; 405 406 lat_info = &parent->child_lat; 407 cur_cookie = atomic_read(&lat_info->scale_cookie); 408 scale_lat = READ_ONCE(lat_info->scale_lat); 409 410 if (cur_cookie < our_cookie) 411 direction = -1; 412 else if (cur_cookie > our_cookie) 413 direction = 1; 414 else 415 return; 416 417 old = atomic_cmpxchg(&iolat->scale_cookie, our_cookie, cur_cookie); 418 419 /* Somebody beat us to the punch, just bail. */ 420 if (old != our_cookie) 421 return; 422 423 if (direction < 0 && iolat->min_lat_nsec) { 424 u64 samples_thresh; 425 426 if (!scale_lat || iolat->min_lat_nsec <= scale_lat) 427 return; 428 429 /* 430 * Sometimes high priority groups are their own worst enemy, so 431 * instead of taking it out on some poor other group that did 5% 432 * or less of the IO's for the last summation just skip this 433 * scale down event. 434 */ 435 samples_thresh = lat_info->nr_samples * 5; 436 samples_thresh = max(1ULL, div64_u64(samples_thresh, 100)); 437 if (iolat->nr_samples <= samples_thresh) 438 return; 439 } 440 441 /* We're as low as we can go. */ 442 if (iolat->rq_depth.max_depth == 1 && direction < 0) { 443 blkcg_use_delay(lat_to_blkg(iolat)); 444 return; 445 } 446 447 /* We're back to the default cookie, unthrottle all the things. */ 448 if (cur_cookie == DEFAULT_SCALE_COOKIE) { 449 blkcg_clear_delay(lat_to_blkg(iolat)); 450 iolat->rq_depth.max_depth = UINT_MAX; 451 wake_up_all(&iolat->rq_wait.wait); 452 return; 453 } 454 455 scale_change(iolat, direction > 0); 456 } 457 458 static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) 459 { 460 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 461 struct blkcg_gq *blkg = bio->bi_blkg; 462 bool issue_as_root = bio_issue_as_root_blkg(bio); 463 464 if (!blk_iolatency_enabled(blkiolat)) 465 return; 466 467 while (blkg && blkg->parent) { 468 struct iolatency_grp *iolat = blkg_to_lat(blkg); 469 if (!iolat) { 470 blkg = blkg->parent; 471 continue; 472 } 473 474 check_scale_change(iolat); 475 __blkcg_iolatency_throttle(rqos, iolat, issue_as_root, 476 (bio->bi_opf & REQ_SWAP) == REQ_SWAP); 477 blkg = blkg->parent; 478 } 479 if (!timer_pending(&blkiolat->timer)) 480 mod_timer(&blkiolat->timer, jiffies + HZ); 481 } 482 483 static void iolatency_record_time(struct iolatency_grp *iolat, 484 struct bio_issue *issue, u64 now, 485 bool issue_as_root) 486 { 487 u64 start = bio_issue_time(issue); 488 u64 req_time; 489 490 /* 491 * Have to do this so we are truncated to the correct time that our 492 * issue is truncated to. 493 */ 494 now = __bio_issue_time(now); 495 496 if (now <= start) 497 return; 498 499 req_time = now - start; 500 501 /* 502 * We don't want to count issue_as_root bio's in the cgroups latency 503 * statistics as it could skew the numbers downwards. 504 */ 505 if (unlikely(issue_as_root && iolat->rq_depth.max_depth != UINT_MAX)) { 506 u64 sub = iolat->min_lat_nsec; 507 if (req_time < sub) 508 blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time); 509 return; 510 } 511 512 latency_stat_record_time(iolat, req_time); 513 } 514 515 #define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC) 516 #define BLKIOLATENCY_MIN_GOOD_SAMPLES 5 517 518 static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now) 519 { 520 struct blkcg_gq *blkg = lat_to_blkg(iolat); 521 struct iolatency_grp *parent; 522 struct child_latency_info *lat_info; 523 struct latency_stat stat; 524 unsigned long flags; 525 int cpu; 526 527 latency_stat_init(iolat, &stat); 528 preempt_disable(); 529 for_each_online_cpu(cpu) { 530 struct latency_stat *s; 531 s = per_cpu_ptr(iolat->stats, cpu); 532 latency_stat_sum(iolat, &stat, s); 533 latency_stat_init(iolat, s); 534 } 535 preempt_enable(); 536 537 parent = blkg_to_lat(blkg->parent); 538 if (!parent) 539 return; 540 541 lat_info = &parent->child_lat; 542 543 iolat_update_total_lat_avg(iolat, &stat); 544 545 /* Everything is ok and we don't need to adjust the scale. */ 546 if (latency_sum_ok(iolat, &stat) && 547 atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE) 548 return; 549 550 /* Somebody beat us to the punch, just bail. */ 551 spin_lock_irqsave(&lat_info->lock, flags); 552 553 latency_stat_sum(iolat, &iolat->cur_stat, &stat); 554 lat_info->nr_samples -= iolat->nr_samples; 555 lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat); 556 iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat); 557 558 if ((lat_info->last_scale_event >= now || 559 now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME)) 560 goto out; 561 562 if (latency_sum_ok(iolat, &iolat->cur_stat) && 563 latency_sum_ok(iolat, &stat)) { 564 if (latency_stat_samples(iolat, &iolat->cur_stat) < 565 BLKIOLATENCY_MIN_GOOD_SAMPLES) 566 goto out; 567 if (lat_info->scale_grp == iolat) { 568 lat_info->last_scale_event = now; 569 scale_cookie_change(iolat->blkiolat, lat_info, true); 570 } 571 } else if (lat_info->scale_lat == 0 || 572 lat_info->scale_lat >= iolat->min_lat_nsec) { 573 lat_info->last_scale_event = now; 574 if (!lat_info->scale_grp || 575 lat_info->scale_lat > iolat->min_lat_nsec) { 576 WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec); 577 lat_info->scale_grp = iolat; 578 } 579 scale_cookie_change(iolat->blkiolat, lat_info, false); 580 } 581 latency_stat_init(iolat, &iolat->cur_stat); 582 out: 583 spin_unlock_irqrestore(&lat_info->lock, flags); 584 } 585 586 static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) 587 { 588 struct blkcg_gq *blkg; 589 struct rq_wait *rqw; 590 struct iolatency_grp *iolat; 591 u64 window_start; 592 u64 now = ktime_to_ns(ktime_get()); 593 bool issue_as_root = bio_issue_as_root_blkg(bio); 594 bool enabled = false; 595 int inflight = 0; 596 597 blkg = bio->bi_blkg; 598 if (!blkg || !bio_flagged(bio, BIO_TRACKED)) 599 return; 600 601 iolat = blkg_to_lat(bio->bi_blkg); 602 if (!iolat) 603 return; 604 605 enabled = blk_iolatency_enabled(iolat->blkiolat); 606 if (!enabled) 607 return; 608 609 while (blkg && blkg->parent) { 610 iolat = blkg_to_lat(blkg); 611 if (!iolat) { 612 blkg = blkg->parent; 613 continue; 614 } 615 rqw = &iolat->rq_wait; 616 617 inflight = atomic_dec_return(&rqw->inflight); 618 WARN_ON_ONCE(inflight < 0); 619 if (iolat->min_lat_nsec == 0) 620 goto next; 621 iolatency_record_time(iolat, &bio->bi_issue, now, 622 issue_as_root); 623 window_start = atomic64_read(&iolat->window_start); 624 if (now > window_start && 625 (now - window_start) >= iolat->cur_win_nsec) { 626 if (atomic64_cmpxchg(&iolat->window_start, 627 window_start, now) == window_start) 628 iolatency_check_latencies(iolat, now); 629 } 630 next: 631 wake_up(&rqw->wait); 632 blkg = blkg->parent; 633 } 634 } 635 636 static void blkcg_iolatency_cleanup(struct rq_qos *rqos, struct bio *bio) 637 { 638 struct blkcg_gq *blkg; 639 640 blkg = bio->bi_blkg; 641 while (blkg && blkg->parent) { 642 struct rq_wait *rqw; 643 struct iolatency_grp *iolat; 644 645 iolat = blkg_to_lat(blkg); 646 if (!iolat) 647 goto next; 648 649 rqw = &iolat->rq_wait; 650 atomic_dec(&rqw->inflight); 651 wake_up(&rqw->wait); 652 next: 653 blkg = blkg->parent; 654 } 655 } 656 657 static void blkcg_iolatency_exit(struct rq_qos *rqos) 658 { 659 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 660 661 del_timer_sync(&blkiolat->timer); 662 blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency); 663 kfree(blkiolat); 664 } 665 666 static struct rq_qos_ops blkcg_iolatency_ops = { 667 .throttle = blkcg_iolatency_throttle, 668 .cleanup = blkcg_iolatency_cleanup, 669 .done_bio = blkcg_iolatency_done_bio, 670 .exit = blkcg_iolatency_exit, 671 }; 672 673 static void blkiolatency_timer_fn(struct timer_list *t) 674 { 675 struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer); 676 struct blkcg_gq *blkg; 677 struct cgroup_subsys_state *pos_css; 678 u64 now = ktime_to_ns(ktime_get()); 679 680 rcu_read_lock(); 681 blkg_for_each_descendant_pre(blkg, pos_css, 682 blkiolat->rqos.q->root_blkg) { 683 struct iolatency_grp *iolat; 684 struct child_latency_info *lat_info; 685 unsigned long flags; 686 u64 cookie; 687 688 /* 689 * We could be exiting, don't access the pd unless we have a 690 * ref on the blkg. 691 */ 692 if (!blkg_tryget(blkg)) 693 continue; 694 695 iolat = blkg_to_lat(blkg); 696 if (!iolat) 697 goto next; 698 699 lat_info = &iolat->child_lat; 700 cookie = atomic_read(&lat_info->scale_cookie); 701 702 if (cookie >= DEFAULT_SCALE_COOKIE) 703 goto next; 704 705 spin_lock_irqsave(&lat_info->lock, flags); 706 if (lat_info->last_scale_event >= now) 707 goto next_lock; 708 709 /* 710 * We scaled down but don't have a scale_grp, scale up and carry 711 * on. 712 */ 713 if (lat_info->scale_grp == NULL) { 714 scale_cookie_change(iolat->blkiolat, lat_info, true); 715 goto next_lock; 716 } 717 718 /* 719 * It's been 5 seconds since our last scale event, clear the 720 * scale grp in case the group that needed the scale down isn't 721 * doing any IO currently. 722 */ 723 if (now - lat_info->last_scale_event >= 724 ((u64)NSEC_PER_SEC * 5)) 725 lat_info->scale_grp = NULL; 726 next_lock: 727 spin_unlock_irqrestore(&lat_info->lock, flags); 728 next: 729 blkg_put(blkg); 730 } 731 rcu_read_unlock(); 732 } 733 734 int blk_iolatency_init(struct request_queue *q) 735 { 736 struct blk_iolatency *blkiolat; 737 struct rq_qos *rqos; 738 int ret; 739 740 blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL); 741 if (!blkiolat) 742 return -ENOMEM; 743 744 rqos = &blkiolat->rqos; 745 rqos->id = RQ_QOS_CGROUP; 746 rqos->ops = &blkcg_iolatency_ops; 747 rqos->q = q; 748 749 rq_qos_add(q, rqos); 750 751 ret = blkcg_activate_policy(q, &blkcg_policy_iolatency); 752 if (ret) { 753 rq_qos_del(q, rqos); 754 kfree(blkiolat); 755 return ret; 756 } 757 758 timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0); 759 760 return 0; 761 } 762 763 /* 764 * return 1 for enabling iolatency, return -1 for disabling iolatency, otherwise 765 * return 0. 766 */ 767 static int iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) 768 { 769 struct iolatency_grp *iolat = blkg_to_lat(blkg); 770 u64 oldval = iolat->min_lat_nsec; 771 772 iolat->min_lat_nsec = val; 773 iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE); 774 iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, 775 BLKIOLATENCY_MAX_WIN_SIZE); 776 777 if (!oldval && val) 778 return 1; 779 if (oldval && !val) 780 return -1; 781 return 0; 782 } 783 784 static void iolatency_clear_scaling(struct blkcg_gq *blkg) 785 { 786 if (blkg->parent) { 787 struct iolatency_grp *iolat = blkg_to_lat(blkg->parent); 788 struct child_latency_info *lat_info; 789 if (!iolat) 790 return; 791 792 lat_info = &iolat->child_lat; 793 spin_lock(&lat_info->lock); 794 atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE); 795 lat_info->last_scale_event = 0; 796 lat_info->scale_grp = NULL; 797 lat_info->scale_lat = 0; 798 spin_unlock(&lat_info->lock); 799 } 800 } 801 802 static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf, 803 size_t nbytes, loff_t off) 804 { 805 struct blkcg *blkcg = css_to_blkcg(of_css(of)); 806 struct blkcg_gq *blkg; 807 struct blkg_conf_ctx ctx; 808 struct iolatency_grp *iolat; 809 char *p, *tok; 810 u64 lat_val = 0; 811 u64 oldval; 812 int ret; 813 int enable = 0; 814 815 ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx); 816 if (ret) 817 return ret; 818 819 iolat = blkg_to_lat(ctx.blkg); 820 p = ctx.body; 821 822 ret = -EINVAL; 823 while ((tok = strsep(&p, " "))) { 824 char key[16]; 825 char val[21]; /* 18446744073709551616 */ 826 827 if (sscanf(tok, "%15[^=]=%20s", key, val) != 2) 828 goto out; 829 830 if (!strcmp(key, "target")) { 831 u64 v; 832 833 if (!strcmp(val, "max")) 834 lat_val = 0; 835 else if (sscanf(val, "%llu", &v) == 1) 836 lat_val = v * NSEC_PER_USEC; 837 else 838 goto out; 839 } else { 840 goto out; 841 } 842 } 843 844 /* Walk up the tree to see if our new val is lower than it should be. */ 845 blkg = ctx.blkg; 846 oldval = iolat->min_lat_nsec; 847 848 enable = iolatency_set_min_lat_nsec(blkg, lat_val); 849 if (enable) { 850 WARN_ON_ONCE(!blk_get_queue(blkg->q)); 851 blkg_get(blkg); 852 } 853 854 if (oldval != iolat->min_lat_nsec) { 855 iolatency_clear_scaling(blkg); 856 } 857 858 ret = 0; 859 out: 860 blkg_conf_finish(&ctx); 861 if (ret == 0 && enable) { 862 struct iolatency_grp *tmp = blkg_to_lat(blkg); 863 struct blk_iolatency *blkiolat = tmp->blkiolat; 864 865 blk_mq_freeze_queue(blkg->q); 866 867 if (enable == 1) 868 atomic_inc(&blkiolat->enabled); 869 else if (enable == -1) 870 atomic_dec(&blkiolat->enabled); 871 else 872 WARN_ON_ONCE(1); 873 874 blk_mq_unfreeze_queue(blkg->q); 875 876 blkg_put(blkg); 877 blk_put_queue(blkg->q); 878 } 879 return ret ?: nbytes; 880 } 881 882 static u64 iolatency_prfill_limit(struct seq_file *sf, 883 struct blkg_policy_data *pd, int off) 884 { 885 struct iolatency_grp *iolat = pd_to_lat(pd); 886 const char *dname = blkg_dev_name(pd->blkg); 887 888 if (!dname || !iolat->min_lat_nsec) 889 return 0; 890 seq_printf(sf, "%s target=%llu\n", 891 dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC)); 892 return 0; 893 } 894 895 static int iolatency_print_limit(struct seq_file *sf, void *v) 896 { 897 blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), 898 iolatency_prfill_limit, 899 &blkcg_policy_iolatency, seq_cft(sf)->private, false); 900 return 0; 901 } 902 903 static size_t iolatency_ssd_stat(struct iolatency_grp *iolat, char *buf, 904 size_t size) 905 { 906 struct latency_stat stat; 907 int cpu; 908 909 latency_stat_init(iolat, &stat); 910 preempt_disable(); 911 for_each_online_cpu(cpu) { 912 struct latency_stat *s; 913 s = per_cpu_ptr(iolat->stats, cpu); 914 latency_stat_sum(iolat, &stat, s); 915 } 916 preempt_enable(); 917 918 if (iolat->rq_depth.max_depth == UINT_MAX) 919 return scnprintf(buf, size, " missed=%llu total=%llu depth=max", 920 (unsigned long long)stat.ps.missed, 921 (unsigned long long)stat.ps.total); 922 return scnprintf(buf, size, " missed=%llu total=%llu depth=%u", 923 (unsigned long long)stat.ps.missed, 924 (unsigned long long)stat.ps.total, 925 iolat->rq_depth.max_depth); 926 } 927 928 static size_t iolatency_pd_stat(struct blkg_policy_data *pd, char *buf, 929 size_t size) 930 { 931 struct iolatency_grp *iolat = pd_to_lat(pd); 932 unsigned long long avg_lat; 933 unsigned long long cur_win; 934 935 if (iolat->ssd) 936 return iolatency_ssd_stat(iolat, buf, size); 937 938 avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC); 939 cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC); 940 if (iolat->rq_depth.max_depth == UINT_MAX) 941 return scnprintf(buf, size, " depth=max avg_lat=%llu win=%llu", 942 avg_lat, cur_win); 943 944 return scnprintf(buf, size, " depth=%u avg_lat=%llu win=%llu", 945 iolat->rq_depth.max_depth, avg_lat, cur_win); 946 } 947 948 949 static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp, int node) 950 { 951 struct iolatency_grp *iolat; 952 953 iolat = kzalloc_node(sizeof(*iolat), gfp, node); 954 if (!iolat) 955 return NULL; 956 iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat), 957 __alignof__(struct latency_stat), gfp); 958 if (!iolat->stats) { 959 kfree(iolat); 960 return NULL; 961 } 962 return &iolat->pd; 963 } 964 965 static void iolatency_pd_init(struct blkg_policy_data *pd) 966 { 967 struct iolatency_grp *iolat = pd_to_lat(pd); 968 struct blkcg_gq *blkg = lat_to_blkg(iolat); 969 struct rq_qos *rqos = blkcg_rq_qos(blkg->q); 970 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 971 u64 now = ktime_to_ns(ktime_get()); 972 int cpu; 973 974 if (blk_queue_nonrot(blkg->q)) 975 iolat->ssd = true; 976 else 977 iolat->ssd = false; 978 979 for_each_possible_cpu(cpu) { 980 struct latency_stat *stat; 981 stat = per_cpu_ptr(iolat->stats, cpu); 982 latency_stat_init(iolat, stat); 983 } 984 985 latency_stat_init(iolat, &iolat->cur_stat); 986 rq_wait_init(&iolat->rq_wait); 987 spin_lock_init(&iolat->child_lat.lock); 988 iolat->rq_depth.queue_depth = blkg->q->nr_requests; 989 iolat->rq_depth.max_depth = UINT_MAX; 990 iolat->rq_depth.default_depth = iolat->rq_depth.queue_depth; 991 iolat->blkiolat = blkiolat; 992 iolat->cur_win_nsec = 100 * NSEC_PER_MSEC; 993 atomic64_set(&iolat->window_start, now); 994 995 /* 996 * We init things in list order, so the pd for the parent may not be 997 * init'ed yet for whatever reason. 998 */ 999 if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) { 1000 struct iolatency_grp *parent = blkg_to_lat(blkg->parent); 1001 atomic_set(&iolat->scale_cookie, 1002 atomic_read(&parent->child_lat.scale_cookie)); 1003 } else { 1004 atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE); 1005 } 1006 1007 atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE); 1008 } 1009 1010 static void iolatency_pd_offline(struct blkg_policy_data *pd) 1011 { 1012 struct iolatency_grp *iolat = pd_to_lat(pd); 1013 struct blkcg_gq *blkg = lat_to_blkg(iolat); 1014 struct blk_iolatency *blkiolat = iolat->blkiolat; 1015 int ret; 1016 1017 ret = iolatency_set_min_lat_nsec(blkg, 0); 1018 if (ret == 1) 1019 atomic_inc(&blkiolat->enabled); 1020 if (ret == -1) 1021 atomic_dec(&blkiolat->enabled); 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 return blkcg_policy_unregister(&blkcg_policy_iolatency); 1059 } 1060 1061 module_init(iolatency_init); 1062 module_exit(iolatency_exit); 1063