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 "blk-rq-qos.h" 76 #include "blk-stat.h" 77 78 #define DEFAULT_SCALE_COOKIE 1000000U 79 80 static struct blkcg_policy blkcg_policy_iolatency; 81 struct iolatency_grp; 82 83 struct blk_iolatency { 84 struct rq_qos rqos; 85 struct timer_list timer; 86 atomic_t enabled; 87 }; 88 89 static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos) 90 { 91 return container_of(rqos, struct blk_iolatency, rqos); 92 } 93 94 static inline bool blk_iolatency_enabled(struct blk_iolatency *blkiolat) 95 { 96 return atomic_read(&blkiolat->enabled) > 0; 97 } 98 99 struct child_latency_info { 100 spinlock_t lock; 101 102 /* Last time we adjusted the scale of everybody. */ 103 u64 last_scale_event; 104 105 /* The latency that we missed. */ 106 u64 scale_lat; 107 108 /* Total io's from all of our children for the last summation. */ 109 u64 nr_samples; 110 111 /* The guy who actually changed the latency numbers. */ 112 struct iolatency_grp *scale_grp; 113 114 /* Cookie to tell if we need to scale up or down. */ 115 atomic_t scale_cookie; 116 }; 117 118 struct percentile_stats { 119 u64 total; 120 u64 missed; 121 }; 122 123 struct latency_stat { 124 union { 125 struct percentile_stats ps; 126 struct blk_rq_stat rqs; 127 }; 128 }; 129 130 struct iolatency_grp { 131 struct blkg_policy_data pd; 132 struct latency_stat __percpu *stats; 133 struct latency_stat cur_stat; 134 struct blk_iolatency *blkiolat; 135 struct rq_depth rq_depth; 136 struct rq_wait rq_wait; 137 atomic64_t window_start; 138 atomic_t scale_cookie; 139 u64 min_lat_nsec; 140 u64 cur_win_nsec; 141 142 /* total running average of our io latency. */ 143 u64 lat_avg; 144 145 /* Our current number of IO's for the last summation. */ 146 u64 nr_samples; 147 148 bool ssd; 149 struct child_latency_info child_lat; 150 }; 151 152 #define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC) 153 #define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC 154 /* 155 * These are the constants used to fake the fixed-point moving average 156 * calculation just like load average. The call to calc_load() folds 157 * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg. The sampling 158 * window size is bucketed to try to approximately calculate average 159 * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows 160 * elapse immediately. Note, windows only elapse with IO activity. Idle 161 * periods extend the most recent window. 162 */ 163 #define BLKIOLATENCY_NR_EXP_FACTORS 5 164 #define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \ 165 (BLKIOLATENCY_NR_EXP_FACTORS - 1)) 166 static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = { 167 2045, // exp(1/600) - 600 samples 168 2039, // exp(1/240) - 240 samples 169 2031, // exp(1/120) - 120 samples 170 2023, // exp(1/80) - 80 samples 171 2014, // exp(1/60) - 60 samples 172 }; 173 174 static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd) 175 { 176 return pd ? container_of(pd, struct iolatency_grp, pd) : NULL; 177 } 178 179 static inline struct iolatency_grp *blkg_to_lat(struct blkcg_gq *blkg) 180 { 181 return pd_to_lat(blkg_to_pd(blkg, &blkcg_policy_iolatency)); 182 } 183 184 static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat) 185 { 186 return pd_to_blkg(&iolat->pd); 187 } 188 189 static inline void latency_stat_init(struct iolatency_grp *iolat, 190 struct latency_stat *stat) 191 { 192 if (iolat->ssd) { 193 stat->ps.total = 0; 194 stat->ps.missed = 0; 195 } else 196 blk_rq_stat_init(&stat->rqs); 197 } 198 199 static inline void latency_stat_sum(struct iolatency_grp *iolat, 200 struct latency_stat *sum, 201 struct latency_stat *stat) 202 { 203 if (iolat->ssd) { 204 sum->ps.total += stat->ps.total; 205 sum->ps.missed += stat->ps.missed; 206 } else 207 blk_rq_stat_sum(&sum->rqs, &stat->rqs); 208 } 209 210 static inline void latency_stat_record_time(struct iolatency_grp *iolat, 211 u64 req_time) 212 { 213 struct latency_stat *stat = get_cpu_ptr(iolat->stats); 214 if (iolat->ssd) { 215 if (req_time >= iolat->min_lat_nsec) 216 stat->ps.missed++; 217 stat->ps.total++; 218 } else 219 blk_rq_stat_add(&stat->rqs, req_time); 220 put_cpu_ptr(stat); 221 } 222 223 static inline bool latency_sum_ok(struct iolatency_grp *iolat, 224 struct latency_stat *stat) 225 { 226 if (iolat->ssd) { 227 u64 thresh = div64_u64(stat->ps.total, 10); 228 thresh = max(thresh, 1ULL); 229 return stat->ps.missed < thresh; 230 } 231 return stat->rqs.mean <= iolat->min_lat_nsec; 232 } 233 234 static inline u64 latency_stat_samples(struct iolatency_grp *iolat, 235 struct latency_stat *stat) 236 { 237 if (iolat->ssd) 238 return stat->ps.total; 239 return stat->rqs.nr_samples; 240 } 241 242 static inline void iolat_update_total_lat_avg(struct iolatency_grp *iolat, 243 struct latency_stat *stat) 244 { 245 int exp_idx; 246 247 if (iolat->ssd) 248 return; 249 250 /* 251 * calc_load() takes in a number stored in fixed point representation. 252 * Because we are using this for IO time in ns, the values stored 253 * are significantly larger than the FIXED_1 denominator (2048). 254 * Therefore, rounding errors in the calculation are negligible and 255 * can be ignored. 256 */ 257 exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1, 258 div64_u64(iolat->cur_win_nsec, 259 BLKIOLATENCY_EXP_BUCKET_SIZE)); 260 iolat->lat_avg = calc_load(iolat->lat_avg, 261 iolatency_exp_factors[exp_idx], 262 stat->rqs.mean); 263 } 264 265 static void iolat_cleanup_cb(struct rq_wait *rqw, void *private_data) 266 { 267 atomic_dec(&rqw->inflight); 268 wake_up(&rqw->wait); 269 } 270 271 static bool iolat_acquire_inflight(struct rq_wait *rqw, void *private_data) 272 { 273 struct iolatency_grp *iolat = private_data; 274 return rq_wait_inc_below(rqw, iolat->rq_depth.max_depth); 275 } 276 277 static void __blkcg_iolatency_throttle(struct rq_qos *rqos, 278 struct iolatency_grp *iolat, 279 bool issue_as_root, 280 bool use_memdelay) 281 { 282 struct rq_wait *rqw = &iolat->rq_wait; 283 unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay); 284 285 if (use_delay) 286 blkcg_schedule_throttle(rqos->q, use_memdelay); 287 288 /* 289 * To avoid priority inversions we want to just take a slot if we are 290 * issuing as root. If we're being killed off there's no point in 291 * delaying things, we may have been killed by OOM so throttling may 292 * make recovery take even longer, so just let the IO's through so the 293 * task can go away. 294 */ 295 if (issue_as_root || fatal_signal_pending(current)) { 296 atomic_inc(&rqw->inflight); 297 return; 298 } 299 300 rq_qos_wait(rqw, iolat, iolat_acquire_inflight, iolat_cleanup_cb); 301 } 302 303 #define SCALE_DOWN_FACTOR 2 304 #define SCALE_UP_FACTOR 4 305 306 static inline unsigned long scale_amount(unsigned long qd, bool up) 307 { 308 return max(up ? qd >> SCALE_UP_FACTOR : qd >> SCALE_DOWN_FACTOR, 1UL); 309 } 310 311 /* 312 * We scale the qd down faster than we scale up, so we need to use this helper 313 * to adjust the scale_cookie accordingly so we don't prematurely get 314 * scale_cookie at DEFAULT_SCALE_COOKIE and unthrottle too much. 315 * 316 * Each group has their own local copy of the last scale cookie they saw, so if 317 * the global scale cookie goes up or down they know which way they need to go 318 * based on their last knowledge of it. 319 */ 320 static void scale_cookie_change(struct blk_iolatency *blkiolat, 321 struct child_latency_info *lat_info, 322 bool up) 323 { 324 unsigned long qd = blkiolat->rqos.q->nr_requests; 325 unsigned long scale = scale_amount(qd, up); 326 unsigned long old = atomic_read(&lat_info->scale_cookie); 327 unsigned long max_scale = qd << 1; 328 unsigned long diff = 0; 329 330 if (old < DEFAULT_SCALE_COOKIE) 331 diff = DEFAULT_SCALE_COOKIE - old; 332 333 if (up) { 334 if (scale + old > DEFAULT_SCALE_COOKIE) 335 atomic_set(&lat_info->scale_cookie, 336 DEFAULT_SCALE_COOKIE); 337 else if (diff > qd) 338 atomic_inc(&lat_info->scale_cookie); 339 else 340 atomic_add(scale, &lat_info->scale_cookie); 341 } else { 342 /* 343 * We don't want to dig a hole so deep that it takes us hours to 344 * dig out of it. Just enough that we don't throttle/unthrottle 345 * with jagged workloads but can still unthrottle once pressure 346 * has sufficiently dissipated. 347 */ 348 if (diff > qd) { 349 if (diff < max_scale) 350 atomic_dec(&lat_info->scale_cookie); 351 } else { 352 atomic_sub(scale, &lat_info->scale_cookie); 353 } 354 } 355 } 356 357 /* 358 * Change the queue depth of the iolatency_grp. We add/subtract 1/16th of the 359 * queue depth at a time so we don't get wild swings and hopefully dial in to 360 * fairer distribution of the overall queue depth. 361 */ 362 static void scale_change(struct iolatency_grp *iolat, bool up) 363 { 364 unsigned long qd = iolat->blkiolat->rqos.q->nr_requests; 365 unsigned long scale = scale_amount(qd, up); 366 unsigned long old = iolat->rq_depth.max_depth; 367 368 if (old > qd) 369 old = qd; 370 371 if (up) { 372 if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat))) 373 return; 374 375 if (old < qd) { 376 old += scale; 377 old = min(old, qd); 378 iolat->rq_depth.max_depth = old; 379 wake_up_all(&iolat->rq_wait.wait); 380 } 381 } else { 382 old >>= 1; 383 iolat->rq_depth.max_depth = max(old, 1UL); 384 } 385 } 386 387 /* Check our parent and see if the scale cookie has changed. */ 388 static void check_scale_change(struct iolatency_grp *iolat) 389 { 390 struct iolatency_grp *parent; 391 struct child_latency_info *lat_info; 392 unsigned int cur_cookie; 393 unsigned int our_cookie = atomic_read(&iolat->scale_cookie); 394 u64 scale_lat; 395 unsigned int old; 396 int direction = 0; 397 398 if (lat_to_blkg(iolat)->parent == NULL) 399 return; 400 401 parent = blkg_to_lat(lat_to_blkg(iolat)->parent); 402 if (!parent) 403 return; 404 405 lat_info = &parent->child_lat; 406 cur_cookie = atomic_read(&lat_info->scale_cookie); 407 scale_lat = READ_ONCE(lat_info->scale_lat); 408 409 if (cur_cookie < our_cookie) 410 direction = -1; 411 else if (cur_cookie > our_cookie) 412 direction = 1; 413 else 414 return; 415 416 old = atomic_cmpxchg(&iolat->scale_cookie, our_cookie, cur_cookie); 417 418 /* Somebody beat us to the punch, just bail. */ 419 if (old != our_cookie) 420 return; 421 422 if (direction < 0 && iolat->min_lat_nsec) { 423 u64 samples_thresh; 424 425 if (!scale_lat || iolat->min_lat_nsec <= scale_lat) 426 return; 427 428 /* 429 * Sometimes high priority groups are their own worst enemy, so 430 * instead of taking it out on some poor other group that did 5% 431 * or less of the IO's for the last summation just skip this 432 * scale down event. 433 */ 434 samples_thresh = lat_info->nr_samples * 5; 435 samples_thresh = max(1ULL, div64_u64(samples_thresh, 100)); 436 if (iolat->nr_samples <= samples_thresh) 437 return; 438 } 439 440 /* We're as low as we can go. */ 441 if (iolat->rq_depth.max_depth == 1 && direction < 0) { 442 blkcg_use_delay(lat_to_blkg(iolat)); 443 return; 444 } 445 446 /* We're back to the default cookie, unthrottle all the things. */ 447 if (cur_cookie == DEFAULT_SCALE_COOKIE) { 448 blkcg_clear_delay(lat_to_blkg(iolat)); 449 iolat->rq_depth.max_depth = UINT_MAX; 450 wake_up_all(&iolat->rq_wait.wait); 451 return; 452 } 453 454 scale_change(iolat, direction > 0); 455 } 456 457 static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) 458 { 459 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 460 struct blkcg_gq *blkg = bio->bi_blkg; 461 bool issue_as_root = bio_issue_as_root_blkg(bio); 462 463 if (!blk_iolatency_enabled(blkiolat)) 464 return; 465 466 while (blkg && blkg->parent) { 467 struct iolatency_grp *iolat = blkg_to_lat(blkg); 468 if (!iolat) { 469 blkg = blkg->parent; 470 continue; 471 } 472 473 check_scale_change(iolat); 474 __blkcg_iolatency_throttle(rqos, iolat, issue_as_root, 475 (bio->bi_opf & REQ_SWAP) == REQ_SWAP); 476 blkg = blkg->parent; 477 } 478 if (!timer_pending(&blkiolat->timer)) 479 mod_timer(&blkiolat->timer, jiffies + HZ); 480 } 481 482 static void iolatency_record_time(struct iolatency_grp *iolat, 483 struct bio_issue *issue, u64 now, 484 bool issue_as_root) 485 { 486 u64 start = bio_issue_time(issue); 487 u64 req_time; 488 489 /* 490 * Have to do this so we are truncated to the correct time that our 491 * issue is truncated to. 492 */ 493 now = __bio_issue_time(now); 494 495 if (now <= start) 496 return; 497 498 req_time = now - start; 499 500 /* 501 * We don't want to count issue_as_root bio's in the cgroups latency 502 * statistics as it could skew the numbers downwards. 503 */ 504 if (unlikely(issue_as_root && iolat->rq_depth.max_depth != UINT_MAX)) { 505 u64 sub = iolat->min_lat_nsec; 506 if (req_time < sub) 507 blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time); 508 return; 509 } 510 511 latency_stat_record_time(iolat, req_time); 512 } 513 514 #define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC) 515 #define BLKIOLATENCY_MIN_GOOD_SAMPLES 5 516 517 static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now) 518 { 519 struct blkcg_gq *blkg = lat_to_blkg(iolat); 520 struct iolatency_grp *parent; 521 struct child_latency_info *lat_info; 522 struct latency_stat stat; 523 unsigned long flags; 524 int cpu; 525 526 latency_stat_init(iolat, &stat); 527 preempt_disable(); 528 for_each_online_cpu(cpu) { 529 struct latency_stat *s; 530 s = per_cpu_ptr(iolat->stats, cpu); 531 latency_stat_sum(iolat, &stat, s); 532 latency_stat_init(iolat, s); 533 } 534 preempt_enable(); 535 536 parent = blkg_to_lat(blkg->parent); 537 if (!parent) 538 return; 539 540 lat_info = &parent->child_lat; 541 542 iolat_update_total_lat_avg(iolat, &stat); 543 544 /* Everything is ok and we don't need to adjust the scale. */ 545 if (latency_sum_ok(iolat, &stat) && 546 atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE) 547 return; 548 549 /* Somebody beat us to the punch, just bail. */ 550 spin_lock_irqsave(&lat_info->lock, flags); 551 552 latency_stat_sum(iolat, &iolat->cur_stat, &stat); 553 lat_info->nr_samples -= iolat->nr_samples; 554 lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat); 555 iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat); 556 557 if ((lat_info->last_scale_event >= now || 558 now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME)) 559 goto out; 560 561 if (latency_sum_ok(iolat, &iolat->cur_stat) && 562 latency_sum_ok(iolat, &stat)) { 563 if (latency_stat_samples(iolat, &iolat->cur_stat) < 564 BLKIOLATENCY_MIN_GOOD_SAMPLES) 565 goto out; 566 if (lat_info->scale_grp == iolat) { 567 lat_info->last_scale_event = now; 568 scale_cookie_change(iolat->blkiolat, lat_info, true); 569 } 570 } else if (lat_info->scale_lat == 0 || 571 lat_info->scale_lat >= iolat->min_lat_nsec) { 572 lat_info->last_scale_event = now; 573 if (!lat_info->scale_grp || 574 lat_info->scale_lat > iolat->min_lat_nsec) { 575 WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec); 576 lat_info->scale_grp = iolat; 577 } 578 scale_cookie_change(iolat->blkiolat, lat_info, false); 579 } 580 latency_stat_init(iolat, &iolat->cur_stat); 581 out: 582 spin_unlock_irqrestore(&lat_info->lock, flags); 583 } 584 585 static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) 586 { 587 struct blkcg_gq *blkg; 588 struct rq_wait *rqw; 589 struct iolatency_grp *iolat; 590 u64 window_start; 591 u64 now = ktime_to_ns(ktime_get()); 592 bool issue_as_root = bio_issue_as_root_blkg(bio); 593 bool enabled = false; 594 595 blkg = bio->bi_blkg; 596 if (!blkg || !bio_flagged(bio, BIO_TRACKED)) 597 return; 598 599 iolat = blkg_to_lat(bio->bi_blkg); 600 if (!iolat) 601 return; 602 603 enabled = blk_iolatency_enabled(iolat->blkiolat); 604 while (blkg && blkg->parent) { 605 iolat = blkg_to_lat(blkg); 606 if (!iolat) { 607 blkg = blkg->parent; 608 continue; 609 } 610 rqw = &iolat->rq_wait; 611 612 atomic_dec(&rqw->inflight); 613 if (!enabled || iolat->min_lat_nsec == 0) 614 goto next; 615 iolatency_record_time(iolat, &bio->bi_issue, now, 616 issue_as_root); 617 window_start = atomic64_read(&iolat->window_start); 618 if (now > window_start && 619 (now - window_start) >= iolat->cur_win_nsec) { 620 if (atomic64_cmpxchg(&iolat->window_start, 621 window_start, now) == window_start) 622 iolatency_check_latencies(iolat, now); 623 } 624 next: 625 wake_up(&rqw->wait); 626 blkg = blkg->parent; 627 } 628 } 629 630 static void blkcg_iolatency_cleanup(struct rq_qos *rqos, struct bio *bio) 631 { 632 struct blkcg_gq *blkg; 633 634 blkg = bio->bi_blkg; 635 while (blkg && blkg->parent) { 636 struct rq_wait *rqw; 637 struct iolatency_grp *iolat; 638 639 iolat = blkg_to_lat(blkg); 640 if (!iolat) 641 goto next; 642 643 rqw = &iolat->rq_wait; 644 atomic_dec(&rqw->inflight); 645 wake_up(&rqw->wait); 646 next: 647 blkg = blkg->parent; 648 } 649 } 650 651 static void blkcg_iolatency_exit(struct rq_qos *rqos) 652 { 653 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 654 655 del_timer_sync(&blkiolat->timer); 656 blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency); 657 kfree(blkiolat); 658 } 659 660 static struct rq_qos_ops blkcg_iolatency_ops = { 661 .throttle = blkcg_iolatency_throttle, 662 .cleanup = blkcg_iolatency_cleanup, 663 .done_bio = blkcg_iolatency_done_bio, 664 .exit = blkcg_iolatency_exit, 665 }; 666 667 static void blkiolatency_timer_fn(struct timer_list *t) 668 { 669 struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer); 670 struct blkcg_gq *blkg; 671 struct cgroup_subsys_state *pos_css; 672 u64 now = ktime_to_ns(ktime_get()); 673 674 rcu_read_lock(); 675 blkg_for_each_descendant_pre(blkg, pos_css, 676 blkiolat->rqos.q->root_blkg) { 677 struct iolatency_grp *iolat; 678 struct child_latency_info *lat_info; 679 unsigned long flags; 680 u64 cookie; 681 682 /* 683 * We could be exiting, don't access the pd unless we have a 684 * ref on the blkg. 685 */ 686 if (!blkg_tryget(blkg)) 687 continue; 688 689 iolat = blkg_to_lat(blkg); 690 if (!iolat) 691 goto next; 692 693 lat_info = &iolat->child_lat; 694 cookie = atomic_read(&lat_info->scale_cookie); 695 696 if (cookie >= DEFAULT_SCALE_COOKIE) 697 goto next; 698 699 spin_lock_irqsave(&lat_info->lock, flags); 700 if (lat_info->last_scale_event >= now) 701 goto next_lock; 702 703 /* 704 * We scaled down but don't have a scale_grp, scale up and carry 705 * on. 706 */ 707 if (lat_info->scale_grp == NULL) { 708 scale_cookie_change(iolat->blkiolat, lat_info, true); 709 goto next_lock; 710 } 711 712 /* 713 * It's been 5 seconds since our last scale event, clear the 714 * scale grp in case the group that needed the scale down isn't 715 * doing any IO currently. 716 */ 717 if (now - lat_info->last_scale_event >= 718 ((u64)NSEC_PER_SEC * 5)) 719 lat_info->scale_grp = NULL; 720 next_lock: 721 spin_unlock_irqrestore(&lat_info->lock, flags); 722 next: 723 blkg_put(blkg); 724 } 725 rcu_read_unlock(); 726 } 727 728 int blk_iolatency_init(struct request_queue *q) 729 { 730 struct blk_iolatency *blkiolat; 731 struct rq_qos *rqos; 732 int ret; 733 734 blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL); 735 if (!blkiolat) 736 return -ENOMEM; 737 738 rqos = &blkiolat->rqos; 739 rqos->id = RQ_QOS_CGROUP; 740 rqos->ops = &blkcg_iolatency_ops; 741 rqos->q = q; 742 743 rq_qos_add(q, rqos); 744 745 ret = blkcg_activate_policy(q, &blkcg_policy_iolatency); 746 if (ret) { 747 rq_qos_del(q, rqos); 748 kfree(blkiolat); 749 return ret; 750 } 751 752 timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0); 753 754 return 0; 755 } 756 757 static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) 758 { 759 struct iolatency_grp *iolat = blkg_to_lat(blkg); 760 struct blk_iolatency *blkiolat = iolat->blkiolat; 761 u64 oldval = iolat->min_lat_nsec; 762 763 iolat->min_lat_nsec = val; 764 iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE); 765 iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, 766 BLKIOLATENCY_MAX_WIN_SIZE); 767 768 if (!oldval && val) 769 atomic_inc(&blkiolat->enabled); 770 if (oldval && !val) 771 atomic_dec(&blkiolat->enabled); 772 } 773 774 static void iolatency_clear_scaling(struct blkcg_gq *blkg) 775 { 776 if (blkg->parent) { 777 struct iolatency_grp *iolat = blkg_to_lat(blkg->parent); 778 struct child_latency_info *lat_info; 779 if (!iolat) 780 return; 781 782 lat_info = &iolat->child_lat; 783 spin_lock(&lat_info->lock); 784 atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE); 785 lat_info->last_scale_event = 0; 786 lat_info->scale_grp = NULL; 787 lat_info->scale_lat = 0; 788 spin_unlock(&lat_info->lock); 789 } 790 } 791 792 static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf, 793 size_t nbytes, loff_t off) 794 { 795 struct blkcg *blkcg = css_to_blkcg(of_css(of)); 796 struct blkcg_gq *blkg; 797 struct blkg_conf_ctx ctx; 798 struct iolatency_grp *iolat; 799 char *p, *tok; 800 u64 lat_val = 0; 801 u64 oldval; 802 int ret; 803 804 ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx); 805 if (ret) 806 return ret; 807 808 iolat = blkg_to_lat(ctx.blkg); 809 p = ctx.body; 810 811 ret = -EINVAL; 812 while ((tok = strsep(&p, " "))) { 813 char key[16]; 814 char val[21]; /* 18446744073709551616 */ 815 816 if (sscanf(tok, "%15[^=]=%20s", key, val) != 2) 817 goto out; 818 819 if (!strcmp(key, "target")) { 820 u64 v; 821 822 if (!strcmp(val, "max")) 823 lat_val = 0; 824 else if (sscanf(val, "%llu", &v) == 1) 825 lat_val = v * NSEC_PER_USEC; 826 else 827 goto out; 828 } else { 829 goto out; 830 } 831 } 832 833 /* Walk up the tree to see if our new val is lower than it should be. */ 834 blkg = ctx.blkg; 835 oldval = iolat->min_lat_nsec; 836 837 iolatency_set_min_lat_nsec(blkg, lat_val); 838 if (oldval != iolat->min_lat_nsec) { 839 iolatency_clear_scaling(blkg); 840 } 841 842 ret = 0; 843 out: 844 blkg_conf_finish(&ctx); 845 return ret ?: nbytes; 846 } 847 848 static u64 iolatency_prfill_limit(struct seq_file *sf, 849 struct blkg_policy_data *pd, int off) 850 { 851 struct iolatency_grp *iolat = pd_to_lat(pd); 852 const char *dname = blkg_dev_name(pd->blkg); 853 854 if (!dname || !iolat->min_lat_nsec) 855 return 0; 856 seq_printf(sf, "%s target=%llu\n", 857 dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC)); 858 return 0; 859 } 860 861 static int iolatency_print_limit(struct seq_file *sf, void *v) 862 { 863 blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), 864 iolatency_prfill_limit, 865 &blkcg_policy_iolatency, seq_cft(sf)->private, false); 866 return 0; 867 } 868 869 static size_t iolatency_ssd_stat(struct iolatency_grp *iolat, char *buf, 870 size_t size) 871 { 872 struct latency_stat stat; 873 int cpu; 874 875 latency_stat_init(iolat, &stat); 876 preempt_disable(); 877 for_each_online_cpu(cpu) { 878 struct latency_stat *s; 879 s = per_cpu_ptr(iolat->stats, cpu); 880 latency_stat_sum(iolat, &stat, s); 881 } 882 preempt_enable(); 883 884 if (iolat->rq_depth.max_depth == UINT_MAX) 885 return scnprintf(buf, size, " missed=%llu total=%llu depth=max", 886 (unsigned long long)stat.ps.missed, 887 (unsigned long long)stat.ps.total); 888 return scnprintf(buf, size, " missed=%llu total=%llu depth=%u", 889 (unsigned long long)stat.ps.missed, 890 (unsigned long long)stat.ps.total, 891 iolat->rq_depth.max_depth); 892 } 893 894 static size_t iolatency_pd_stat(struct blkg_policy_data *pd, char *buf, 895 size_t size) 896 { 897 struct iolatency_grp *iolat = pd_to_lat(pd); 898 unsigned long long avg_lat; 899 unsigned long long cur_win; 900 901 if (iolat->ssd) 902 return iolatency_ssd_stat(iolat, buf, size); 903 904 avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC); 905 cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC); 906 if (iolat->rq_depth.max_depth == UINT_MAX) 907 return scnprintf(buf, size, " depth=max avg_lat=%llu win=%llu", 908 avg_lat, cur_win); 909 910 return scnprintf(buf, size, " depth=%u avg_lat=%llu win=%llu", 911 iolat->rq_depth.max_depth, avg_lat, cur_win); 912 } 913 914 915 static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp, int node) 916 { 917 struct iolatency_grp *iolat; 918 919 iolat = kzalloc_node(sizeof(*iolat), gfp, node); 920 if (!iolat) 921 return NULL; 922 iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat), 923 __alignof__(struct latency_stat), gfp); 924 if (!iolat->stats) { 925 kfree(iolat); 926 return NULL; 927 } 928 return &iolat->pd; 929 } 930 931 static void iolatency_pd_init(struct blkg_policy_data *pd) 932 { 933 struct iolatency_grp *iolat = pd_to_lat(pd); 934 struct blkcg_gq *blkg = lat_to_blkg(iolat); 935 struct rq_qos *rqos = blkcg_rq_qos(blkg->q); 936 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 937 u64 now = ktime_to_ns(ktime_get()); 938 int cpu; 939 940 if (blk_queue_nonrot(blkg->q)) 941 iolat->ssd = true; 942 else 943 iolat->ssd = false; 944 945 for_each_possible_cpu(cpu) { 946 struct latency_stat *stat; 947 stat = per_cpu_ptr(iolat->stats, cpu); 948 latency_stat_init(iolat, stat); 949 } 950 951 latency_stat_init(iolat, &iolat->cur_stat); 952 rq_wait_init(&iolat->rq_wait); 953 spin_lock_init(&iolat->child_lat.lock); 954 iolat->rq_depth.queue_depth = blkg->q->nr_requests; 955 iolat->rq_depth.max_depth = UINT_MAX; 956 iolat->rq_depth.default_depth = iolat->rq_depth.queue_depth; 957 iolat->blkiolat = blkiolat; 958 iolat->cur_win_nsec = 100 * NSEC_PER_MSEC; 959 atomic64_set(&iolat->window_start, now); 960 961 /* 962 * We init things in list order, so the pd for the parent may not be 963 * init'ed yet for whatever reason. 964 */ 965 if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) { 966 struct iolatency_grp *parent = blkg_to_lat(blkg->parent); 967 atomic_set(&iolat->scale_cookie, 968 atomic_read(&parent->child_lat.scale_cookie)); 969 } else { 970 atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE); 971 } 972 973 atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE); 974 } 975 976 static void iolatency_pd_offline(struct blkg_policy_data *pd) 977 { 978 struct iolatency_grp *iolat = pd_to_lat(pd); 979 struct blkcg_gq *blkg = lat_to_blkg(iolat); 980 981 iolatency_set_min_lat_nsec(blkg, 0); 982 iolatency_clear_scaling(blkg); 983 } 984 985 static void iolatency_pd_free(struct blkg_policy_data *pd) 986 { 987 struct iolatency_grp *iolat = pd_to_lat(pd); 988 free_percpu(iolat->stats); 989 kfree(iolat); 990 } 991 992 static struct cftype iolatency_files[] = { 993 { 994 .name = "latency", 995 .flags = CFTYPE_NOT_ON_ROOT, 996 .seq_show = iolatency_print_limit, 997 .write = iolatency_set_limit, 998 }, 999 {} 1000 }; 1001 1002 static struct blkcg_policy blkcg_policy_iolatency = { 1003 .dfl_cftypes = iolatency_files, 1004 .pd_alloc_fn = iolatency_pd_alloc, 1005 .pd_init_fn = iolatency_pd_init, 1006 .pd_offline_fn = iolatency_pd_offline, 1007 .pd_free_fn = iolatency_pd_free, 1008 .pd_stat_fn = iolatency_pd_stat, 1009 }; 1010 1011 static int __init iolatency_init(void) 1012 { 1013 return blkcg_policy_register(&blkcg_policy_iolatency); 1014 } 1015 1016 static void __exit iolatency_exit(void) 1017 { 1018 return blkcg_policy_unregister(&blkcg_policy_iolatency); 1019 } 1020 1021 module_init(iolatency_init); 1022 module_exit(iolatency_exit); 1023