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   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
  84static struct blkcg_policy blkcg_policy_iolatency;
  85struct iolatency_grp;
  86
  87struct 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
 103static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos)
 104{
 105	return container_of(rqos, struct blk_iolatency, rqos);
 106}
 107
 108struct 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
 127struct percentile_stats {
 128	u64 total;
 129	u64 missed;
 130};
 131
 132struct latency_stat {
 133	union {
 134		struct percentile_stats ps;
 135		struct blk_rq_stat rqs;
 136	};
 137};
 138
 139struct iolatency_grp {
 140	struct blkg_policy_data pd;
 141	struct latency_stat __percpu *stats;
 142	struct latency_stat cur_stat;
 143	struct blk_iolatency *blkiolat;
 144	unsigned int max_depth;
 145	struct rq_wait rq_wait;
 146	atomic64_t window_start;
 147	atomic_t scale_cookie;
 148	u64 min_lat_nsec;
 149	u64 cur_win_nsec;
 150
 151	/* total running average of our io latency. */
 152	u64 lat_avg;
 153
 154	/* Our current number of IO's for the last summation. */
 155	u64 nr_samples;
 156
 157	bool ssd;
 158	struct child_latency_info child_lat;
 159};
 160
 161#define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC)
 162#define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC
 163/*
 164 * These are the constants used to fake the fixed-point moving average
 165 * calculation just like load average.  The call to calc_load() folds
 166 * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg.  The sampling
 167 * window size is bucketed to try to approximately calculate average
 168 * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows
 169 * elapse immediately.  Note, windows only elapse with IO activity.  Idle
 170 * periods extend the most recent window.
 171 */
 172#define BLKIOLATENCY_NR_EXP_FACTORS 5
 173#define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \
 174				      (BLKIOLATENCY_NR_EXP_FACTORS - 1))
 175static 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
 183static 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
 188static 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
 193static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat)
 194{
 195	return pd_to_blkg(&iolat->pd);
 196}
 197
 198static 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
 208static 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
 219static 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
 232static 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
 243static 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
 251static 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
 274static void iolat_cleanup_cb(struct rq_wait *rqw, void *private_data)
 275{
 276	atomic_dec(&rqw->inflight);
 277	wake_up(&rqw->wait);
 278}
 279
 280static bool iolat_acquire_inflight(struct rq_wait *rqw, void *private_data)
 281{
 282	struct iolatency_grp *iolat = private_data;
 283	return rq_wait_inc_below(rqw, iolat->max_depth);
 284}
 285
 286static 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->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
 315static 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 */
 329static 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.disk->queue->nr_requests;
 334	unsigned long scale = scale_amount(qd, up);
 335	unsigned long old = atomic_read(&lat_info->scale_cookie);
 336	unsigned long max_scale = qd << 1;
 337	unsigned long diff = 0;
 338
 339	if (old < DEFAULT_SCALE_COOKIE)
 340		diff = DEFAULT_SCALE_COOKIE - old;
 341
 342	if (up) {
 343		if (scale + old > DEFAULT_SCALE_COOKIE)
 344			atomic_set(&lat_info->scale_cookie,
 345				   DEFAULT_SCALE_COOKIE);
 346		else if (diff > qd)
 347			atomic_inc(&lat_info->scale_cookie);
 348		else
 349			atomic_add(scale, &lat_info->scale_cookie);
 350	} else {
 351		/*
 352		 * We don't want to dig a hole so deep that it takes us hours to
 353		 * dig out of it.  Just enough that we don't throttle/unthrottle
 354		 * with jagged workloads but can still unthrottle once pressure
 355		 * has sufficiently dissipated.
 356		 */
 357		if (diff > qd) {
 358			if (diff < max_scale)
 359				atomic_dec(&lat_info->scale_cookie);
 360		} else {
 361			atomic_sub(scale, &lat_info->scale_cookie);
 362		}
 363	}
 364}
 365
 366/*
 367 * Change the queue depth of the iolatency_grp.  We add 1/16th of the
 368 * queue depth at a time so we don't get wild swings and hopefully dial in to
 369 * fairer distribution of the overall queue depth.  We halve the queue depth
 370 * at a time so we can scale down queue depth quickly from default unlimited
 371 * to target.
 372 */
 373static void scale_change(struct iolatency_grp *iolat, bool up)
 374{
 375	unsigned long qd = iolat->blkiolat->rqos.disk->queue->nr_requests;
 376	unsigned long scale = scale_amount(qd, up);
 377	unsigned long old = iolat->max_depth;
 378
 379	if (old > qd)
 380		old = qd;
 381
 382	if (up) {
 383		if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat)))
 384			return;
 385
 386		if (old < qd) {
 387			old += scale;
 388			old = min(old, qd);
 389			iolat->max_depth = old;
 390			wake_up_all(&iolat->rq_wait.wait);
 391		}
 392	} else {
 393		old >>= 1;
 394		iolat->max_depth = max(old, 1UL);
 395	}
 396}
 397
 398/* Check our parent and see if the scale cookie has changed. */
 399static void check_scale_change(struct iolatency_grp *iolat)
 400{
 401	struct iolatency_grp *parent;
 402	struct child_latency_info *lat_info;
 403	unsigned int cur_cookie;
 404	unsigned int our_cookie = atomic_read(&iolat->scale_cookie);
 405	u64 scale_lat;
 406	int direction = 0;
 407
 408	parent = blkg_to_lat(lat_to_blkg(iolat)->parent);
 409	if (!parent)
 410		return;
 411
 412	lat_info = &parent->child_lat;
 413	cur_cookie = atomic_read(&lat_info->scale_cookie);
 414	scale_lat = READ_ONCE(lat_info->scale_lat);
 415
 416	if (cur_cookie < our_cookie)
 417		direction = -1;
 418	else if (cur_cookie > our_cookie)
 419		direction = 1;
 420	else
 421		return;
 422
 423	if (!atomic_try_cmpxchg(&iolat->scale_cookie, &our_cookie, cur_cookie)) {
 424		/* Somebody beat us to the punch, just bail. */
 425		return;
 426	}
 427
 428	if (direction < 0 && iolat->min_lat_nsec) {
 429		u64 samples_thresh;
 430
 431		if (!scale_lat || iolat->min_lat_nsec <= scale_lat)
 432			return;
 433
 434		/*
 435		 * Sometimes high priority groups are their own worst enemy, so
 436		 * instead of taking it out on some poor other group that did 5%
 437		 * or less of the IO's for the last summation just skip this
 438		 * scale down event.
 439		 */
 440		samples_thresh = lat_info->nr_samples * 5;
 441		samples_thresh = max(1ULL, div64_u64(samples_thresh, 100));
 442		if (iolat->nr_samples <= samples_thresh)
 443			return;
 444	}
 445
 446	/* We're as low as we can go. */
 447	if (iolat->max_depth == 1 && direction < 0) {
 448		blkcg_use_delay(lat_to_blkg(iolat));
 449		return;
 450	}
 451
 452	/* We're back to the default cookie, unthrottle all the things. */
 453	if (cur_cookie == DEFAULT_SCALE_COOKIE) {
 454		blkcg_clear_delay(lat_to_blkg(iolat));
 455		iolat->max_depth = UINT_MAX;
 456		wake_up_all(&iolat->rq_wait.wait);
 457		return;
 458	}
 459
 460	scale_change(iolat, direction > 0);
 461}
 462
 463static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio)
 464{
 465	struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
 466	struct blkcg_gq *blkg = bio->bi_blkg;
 467	bool issue_as_root = bio_issue_as_root_blkg(bio);
 468
 469	if (!blkiolat->enabled)
 470		return;
 471
 472	while (blkg && blkg->parent) {
 473		struct iolatency_grp *iolat = blkg_to_lat(blkg);
 474		if (!iolat) {
 475			blkg = blkg->parent;
 476			continue;
 477		}
 478
 479		check_scale_change(iolat);
 480		__blkcg_iolatency_throttle(rqos, iolat, issue_as_root,
 481				     (bio->bi_opf & REQ_SWAP) == REQ_SWAP);
 482		blkg = blkg->parent;
 483	}
 484	if (!timer_pending(&blkiolat->timer))
 485		mod_timer(&blkiolat->timer, jiffies + HZ);
 486}
 487
 488static void iolatency_record_time(struct iolatency_grp *iolat,
 489				  struct bio_issue *issue, u64 now,
 490				  bool issue_as_root)
 491{
 492	u64 start = bio_issue_time(issue);
 493	u64 req_time;
 494
 495	/*
 496	 * Have to do this so we are truncated to the correct time that our
 497	 * issue is truncated to.
 498	 */
 499	now = __bio_issue_time(now);
 500
 501	if (now <= start)
 502		return;
 503
 504	req_time = now - start;
 505
 506	/*
 507	 * We don't want to count issue_as_root bio's in the cgroups latency
 508	 * statistics as it could skew the numbers downwards.
 509	 */
 510	if (unlikely(issue_as_root && iolat->max_depth != UINT_MAX)) {
 511		u64 sub = iolat->min_lat_nsec;
 512		if (req_time < sub)
 513			blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time);
 514		return;
 515	}
 516
 517	latency_stat_record_time(iolat, req_time);
 518}
 519
 520#define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC)
 521#define BLKIOLATENCY_MIN_GOOD_SAMPLES 5
 522
 523static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now)
 524{
 525	struct blkcg_gq *blkg = lat_to_blkg(iolat);
 526	struct iolatency_grp *parent;
 527	struct child_latency_info *lat_info;
 528	struct latency_stat stat;
 529	unsigned long flags;
 530	int cpu;
 531
 532	latency_stat_init(iolat, &stat);
 533	preempt_disable();
 534	for_each_online_cpu(cpu) {
 535		struct latency_stat *s;
 536		s = per_cpu_ptr(iolat->stats, cpu);
 537		latency_stat_sum(iolat, &stat, s);
 538		latency_stat_init(iolat, s);
 539	}
 540	preempt_enable();
 541
 542	parent = blkg_to_lat(blkg->parent);
 543	if (!parent)
 544		return;
 545
 546	lat_info = &parent->child_lat;
 547
 548	iolat_update_total_lat_avg(iolat, &stat);
 549
 550	/* Everything is ok and we don't need to adjust the scale. */
 551	if (latency_sum_ok(iolat, &stat) &&
 552	    atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE)
 553		return;
 554
 555	/* Somebody beat us to the punch, just bail. */
 556	spin_lock_irqsave(&lat_info->lock, flags);
 557
 558	latency_stat_sum(iolat, &iolat->cur_stat, &stat);
 559	lat_info->nr_samples -= iolat->nr_samples;
 560	lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat);
 561	iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat);
 562
 563	if ((lat_info->last_scale_event >= now ||
 564	    now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME))
 565		goto out;
 566
 567	if (latency_sum_ok(iolat, &iolat->cur_stat) &&
 568	    latency_sum_ok(iolat, &stat)) {
 569		if (latency_stat_samples(iolat, &iolat->cur_stat) <
 570		    BLKIOLATENCY_MIN_GOOD_SAMPLES)
 571			goto out;
 572		if (lat_info->scale_grp == iolat) {
 573			lat_info->last_scale_event = now;
 574			scale_cookie_change(iolat->blkiolat, lat_info, true);
 575		}
 576	} else if (lat_info->scale_lat == 0 ||
 577		   lat_info->scale_lat >= iolat->min_lat_nsec) {
 578		lat_info->last_scale_event = now;
 579		if (!lat_info->scale_grp ||
 580		    lat_info->scale_lat > iolat->min_lat_nsec) {
 581			WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec);
 582			lat_info->scale_grp = iolat;
 583		}
 584		scale_cookie_change(iolat->blkiolat, lat_info, false);
 585	}
 586	latency_stat_init(iolat, &iolat->cur_stat);
 587out:
 588	spin_unlock_irqrestore(&lat_info->lock, flags);
 589}
 590
 591static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio)
 592{
 593	struct blkcg_gq *blkg;
 594	struct rq_wait *rqw;
 595	struct iolatency_grp *iolat;
 596	u64 window_start;
 597	u64 now;
 598	bool issue_as_root = bio_issue_as_root_blkg(bio);
 599	int inflight = 0;
 600
 601	blkg = bio->bi_blkg;
 602	if (!blkg || !bio_flagged(bio, BIO_QOS_THROTTLED))
 603		return;
 604
 605	iolat = blkg_to_lat(bio->bi_blkg);
 606	if (!iolat)
 607		return;
 608
 609	if (!iolat->blkiolat->enabled)
 610		return;
 611
 612	now = blk_time_get_ns();
 613	while (blkg && blkg->parent) {
 614		iolat = blkg_to_lat(blkg);
 615		if (!iolat) {
 616			blkg = blkg->parent;
 617			continue;
 618		}
 619		rqw = &iolat->rq_wait;
 620
 621		inflight = atomic_dec_return(&rqw->inflight);
 622		WARN_ON_ONCE(inflight < 0);
 623		/*
 624		 * If bi_status is BLK_STS_AGAIN, the bio wasn't actually
 625		 * submitted, so do not account for it.
 626		 */
 627		if (iolat->min_lat_nsec && bio->bi_status != BLK_STS_AGAIN) {
 628			iolatency_record_time(iolat, &bio->bi_issue, now,
 629					      issue_as_root);
 630			window_start = atomic64_read(&iolat->window_start);
 631			if (now > window_start &&
 632			    (now - window_start) >= iolat->cur_win_nsec) {
 633				if (atomic64_try_cmpxchg(&iolat->window_start,
 634							 &window_start, now))
 635					iolatency_check_latencies(iolat, now);
 636			}
 637		}
 638		wake_up(&rqw->wait);
 639		blkg = blkg->parent;
 640	}
 641}
 642
 643static void blkcg_iolatency_exit(struct rq_qos *rqos)
 644{
 645	struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
 646
 647	timer_shutdown_sync(&blkiolat->timer);
 648	flush_work(&blkiolat->enable_work);
 649	blkcg_deactivate_policy(rqos->disk, &blkcg_policy_iolatency);
 650	kfree(blkiolat);
 651}
 652
 653static const struct rq_qos_ops blkcg_iolatency_ops = {
 654	.throttle = blkcg_iolatency_throttle,
 655	.done_bio = blkcg_iolatency_done_bio,
 656	.exit = blkcg_iolatency_exit,
 657};
 658
 659static void blkiolatency_timer_fn(struct timer_list *t)
 660{
 661	struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer);
 662	struct blkcg_gq *blkg;
 663	struct cgroup_subsys_state *pos_css;
 664	u64 now = blk_time_get_ns();
 665
 666	rcu_read_lock();
 667	blkg_for_each_descendant_pre(blkg, pos_css,
 668				     blkiolat->rqos.disk->queue->root_blkg) {
 669		struct iolatency_grp *iolat;
 670		struct child_latency_info *lat_info;
 671		unsigned long flags;
 672		u64 cookie;
 673
 674		/*
 675		 * We could be exiting, don't access the pd unless we have a
 676		 * ref on the blkg.
 677		 */
 678		if (!blkg_tryget(blkg))
 679			continue;
 680
 681		iolat = blkg_to_lat(blkg);
 682		if (!iolat)
 683			goto next;
 684
 685		lat_info = &iolat->child_lat;
 686		cookie = atomic_read(&lat_info->scale_cookie);
 687
 688		if (cookie >= DEFAULT_SCALE_COOKIE)
 689			goto next;
 690
 691		spin_lock_irqsave(&lat_info->lock, flags);
 692		if (lat_info->last_scale_event >= now)
 693			goto next_lock;
 694
 695		/*
 696		 * We scaled down but don't have a scale_grp, scale up and carry
 697		 * on.
 698		 */
 699		if (lat_info->scale_grp == NULL) {
 700			scale_cookie_change(iolat->blkiolat, lat_info, true);
 701			goto next_lock;
 702		}
 703
 704		/*
 705		 * It's been 5 seconds since our last scale event, clear the
 706		 * scale grp in case the group that needed the scale down isn't
 707		 * doing any IO currently.
 708		 */
 709		if (now - lat_info->last_scale_event >=
 710		    ((u64)NSEC_PER_SEC * 5))
 711			lat_info->scale_grp = NULL;
 712next_lock:
 713		spin_unlock_irqrestore(&lat_info->lock, flags);
 714next:
 715		blkg_put(blkg);
 716	}
 717	rcu_read_unlock();
 718}
 719
 720/**
 721 * blkiolatency_enable_work_fn - Enable or disable iolatency on the device
 722 * @work: enable_work of the blk_iolatency of interest
 723 *
 724 * iolatency needs to keep track of the number of in-flight IOs per cgroup. This
 725 * is relatively expensive as it involves walking up the hierarchy twice for
 726 * every IO. Thus, if iolatency is not enabled in any cgroup for the device, we
 727 * want to disable the in-flight tracking.
 728 *
 729 * We have to make sure that the counting is balanced - we don't want to leak
 730 * the in-flight counts by disabling accounting in the completion path while IOs
 731 * are in flight. This is achieved by ensuring that no IO is in flight by
 732 * freezing the queue while flipping ->enabled. As this requires a sleepable
 733 * context, ->enabled flipping is punted to this work function.
 734 */
 735static void blkiolatency_enable_work_fn(struct work_struct *work)
 736{
 737	struct blk_iolatency *blkiolat = container_of(work, struct blk_iolatency,
 738						      enable_work);
 739	bool enabled;
 740
 741	/*
 742	 * There can only be one instance of this function running for @blkiolat
 743	 * and it's guaranteed to be executed at least once after the latest
 744	 * ->enabled_cnt modification. Acting on the latest ->enable_cnt is
 745	 * sufficient.
 746	 *
 747	 * Also, we know @blkiolat is safe to access as ->enable_work is flushed
 748	 * in blkcg_iolatency_exit().
 749	 */
 750	enabled = atomic_read(&blkiolat->enable_cnt);
 751	if (enabled != blkiolat->enabled) {
 752		blk_mq_freeze_queue(blkiolat->rqos.disk->queue);
 753		blkiolat->enabled = enabled;
 754		blk_mq_unfreeze_queue(blkiolat->rqos.disk->queue);
 755	}
 756}
 757
 758static int blk_iolatency_init(struct gendisk *disk)
 759{
 760	struct blk_iolatency *blkiolat;
 761	int ret;
 762
 763	blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL);
 764	if (!blkiolat)
 765		return -ENOMEM;
 766
 767	ret = rq_qos_add(&blkiolat->rqos, disk, RQ_QOS_LATENCY,
 768			 &blkcg_iolatency_ops);
 769	if (ret)
 770		goto err_free;
 771	ret = blkcg_activate_policy(disk, &blkcg_policy_iolatency);
 772	if (ret)
 773		goto err_qos_del;
 774
 775	timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0);
 776	INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn);
 777
 778	return 0;
 779
 780err_qos_del:
 781	rq_qos_del(&blkiolat->rqos);
 782err_free:
 783	kfree(blkiolat);
 784	return ret;
 785}
 786
 787static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val)
 788{
 789	struct iolatency_grp *iolat = blkg_to_lat(blkg);
 790	struct blk_iolatency *blkiolat = iolat->blkiolat;
 791	u64 oldval = iolat->min_lat_nsec;
 792
 793	iolat->min_lat_nsec = val;
 794	iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE);
 795	iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec,
 796				    BLKIOLATENCY_MAX_WIN_SIZE);
 797
 798	if (!oldval && val) {
 799		if (atomic_inc_return(&blkiolat->enable_cnt) == 1)
 800			schedule_work(&blkiolat->enable_work);
 801	}
 802	if (oldval && !val) {
 803		blkcg_clear_delay(blkg);
 804		if (atomic_dec_return(&blkiolat->enable_cnt) == 0)
 805			schedule_work(&blkiolat->enable_work);
 806	}
 807}
 808
 809static void iolatency_clear_scaling(struct blkcg_gq *blkg)
 810{
 811	if (blkg->parent) {
 812		struct iolatency_grp *iolat = blkg_to_lat(blkg->parent);
 813		struct child_latency_info *lat_info;
 814		if (!iolat)
 815			return;
 816
 817		lat_info = &iolat->child_lat;
 818		spin_lock(&lat_info->lock);
 819		atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE);
 820		lat_info->last_scale_event = 0;
 821		lat_info->scale_grp = NULL;
 822		lat_info->scale_lat = 0;
 823		spin_unlock(&lat_info->lock);
 824	}
 825}
 826
 827static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf,
 828			     size_t nbytes, loff_t off)
 829{
 830	struct blkcg *blkcg = css_to_blkcg(of_css(of));
 831	struct blkcg_gq *blkg;
 832	struct blkg_conf_ctx ctx;
 833	struct iolatency_grp *iolat;
 834	char *p, *tok;
 835	u64 lat_val = 0;
 836	u64 oldval;
 837	int ret;
 838
 839	blkg_conf_init(&ctx, buf);
 840
 841	ret = blkg_conf_open_bdev(&ctx);
 842	if (ret)
 843		goto out;
 844
 845	/*
 846	 * blk_iolatency_init() may fail after rq_qos_add() succeeds which can
 847	 * confuse iolat_rq_qos() test. Make the test and init atomic.
 848	 */
 849	lockdep_assert_held(&ctx.bdev->bd_queue->rq_qos_mutex);
 850	if (!iolat_rq_qos(ctx.bdev->bd_queue))
 851		ret = blk_iolatency_init(ctx.bdev->bd_disk);
 852	if (ret)
 853		goto out;
 854
 855	ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, &ctx);
 856	if (ret)
 857		goto out;
 858
 859	iolat = blkg_to_lat(ctx.blkg);
 860	p = ctx.body;
 861
 862	ret = -EINVAL;
 863	while ((tok = strsep(&p, " "))) {
 864		char key[16];
 865		char val[21];	/* 18446744073709551616 */
 866
 867		if (sscanf(tok, "%15[^=]=%20s", key, val) != 2)
 868			goto out;
 869
 870		if (!strcmp(key, "target")) {
 871			u64 v;
 872
 873			if (!strcmp(val, "max"))
 874				lat_val = 0;
 875			else if (sscanf(val, "%llu", &v) == 1)
 876				lat_val = v * NSEC_PER_USEC;
 877			else
 878				goto out;
 879		} else {
 880			goto out;
 881		}
 882	}
 883
 884	/* Walk up the tree to see if our new val is lower than it should be. */
 885	blkg = ctx.blkg;
 886	oldval = iolat->min_lat_nsec;
 887
 888	iolatency_set_min_lat_nsec(blkg, lat_val);
 889	if (oldval != iolat->min_lat_nsec)
 890		iolatency_clear_scaling(blkg);
 891	ret = 0;
 892out:
 893	blkg_conf_exit(&ctx);
 894	return ret ?: nbytes;
 895}
 896
 897static u64 iolatency_prfill_limit(struct seq_file *sf,
 898				  struct blkg_policy_data *pd, int off)
 899{
 900	struct iolatency_grp *iolat = pd_to_lat(pd);
 901	const char *dname = blkg_dev_name(pd->blkg);
 902
 903	if (!dname || !iolat->min_lat_nsec)
 904		return 0;
 905	seq_printf(sf, "%s target=%llu\n",
 906		   dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC));
 907	return 0;
 908}
 909
 910static int iolatency_print_limit(struct seq_file *sf, void *v)
 911{
 912	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
 913			  iolatency_prfill_limit,
 914			  &blkcg_policy_iolatency, seq_cft(sf)->private, false);
 915	return 0;
 916}
 917
 918static void iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s)
 919{
 920	struct latency_stat stat;
 921	int cpu;
 922
 923	latency_stat_init(iolat, &stat);
 924	preempt_disable();
 925	for_each_online_cpu(cpu) {
 926		struct latency_stat *s;
 927		s = per_cpu_ptr(iolat->stats, cpu);
 928		latency_stat_sum(iolat, &stat, s);
 929	}
 930	preempt_enable();
 931
 932	if (iolat->max_depth == UINT_MAX)
 933		seq_printf(s, " missed=%llu total=%llu depth=max",
 934			(unsigned long long)stat.ps.missed,
 935			(unsigned long long)stat.ps.total);
 936	else
 937		seq_printf(s, " missed=%llu total=%llu depth=%u",
 938			(unsigned long long)stat.ps.missed,
 939			(unsigned long long)stat.ps.total,
 940			iolat->max_depth);
 941}
 942
 943static void iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 944{
 945	struct iolatency_grp *iolat = pd_to_lat(pd);
 946	unsigned long long avg_lat;
 947	unsigned long long cur_win;
 948
 949	if (!blkcg_debug_stats)
 950		return;
 951
 952	if (iolat->ssd)
 953		return iolatency_ssd_stat(iolat, s);
 954
 955	avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC);
 956	cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC);
 957	if (iolat->max_depth == UINT_MAX)
 958		seq_printf(s, " depth=max avg_lat=%llu win=%llu",
 959			avg_lat, cur_win);
 960	else
 961		seq_printf(s, " depth=%u avg_lat=%llu win=%llu",
 962			iolat->max_depth, avg_lat, cur_win);
 963}
 964
 965static struct blkg_policy_data *iolatency_pd_alloc(struct gendisk *disk,
 966		struct blkcg *blkcg, gfp_t gfp)
 967{
 968	struct iolatency_grp *iolat;
 969
 970	iolat = kzalloc_node(sizeof(*iolat), gfp, disk->node_id);
 971	if (!iolat)
 972		return NULL;
 973	iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat),
 974				       __alignof__(struct latency_stat), gfp);
 975	if (!iolat->stats) {
 976		kfree(iolat);
 977		return NULL;
 978	}
 979	return &iolat->pd;
 980}
 981
 982static void iolatency_pd_init(struct blkg_policy_data *pd)
 983{
 984	struct iolatency_grp *iolat = pd_to_lat(pd);
 985	struct blkcg_gq *blkg = lat_to_blkg(iolat);
 986	struct rq_qos *rqos = iolat_rq_qos(blkg->q);
 987	struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
 988	u64 now = blk_time_get_ns();
 989	int cpu;
 990
 991	if (blk_queue_nonrot(blkg->q))
 992		iolat->ssd = true;
 993	else
 994		iolat->ssd = false;
 995
 996	for_each_possible_cpu(cpu) {
 997		struct latency_stat *stat;
 998		stat = per_cpu_ptr(iolat->stats, cpu);
 999		latency_stat_init(iolat, stat);
1000	}
1001
1002	latency_stat_init(iolat, &iolat->cur_stat);
1003	rq_wait_init(&iolat->rq_wait);
1004	spin_lock_init(&iolat->child_lat.lock);
1005	iolat->max_depth = UINT_MAX;
1006	iolat->blkiolat = blkiolat;
1007	iolat->cur_win_nsec = 100 * NSEC_PER_MSEC;
1008	atomic64_set(&iolat->window_start, now);
1009
1010	/*
1011	 * We init things in list order, so the pd for the parent may not be
1012	 * init'ed yet for whatever reason.
1013	 */
1014	if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) {
1015		struct iolatency_grp *parent = blkg_to_lat(blkg->parent);
1016		atomic_set(&iolat->scale_cookie,
1017			   atomic_read(&parent->child_lat.scale_cookie));
1018	} else {
1019		atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE);
1020	}
1021
1022	atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE);
1023}
1024
1025static void iolatency_pd_offline(struct blkg_policy_data *pd)
1026{
1027	struct iolatency_grp *iolat = pd_to_lat(pd);
1028	struct blkcg_gq *blkg = lat_to_blkg(iolat);
1029
1030	iolatency_set_min_lat_nsec(blkg, 0);
1031	iolatency_clear_scaling(blkg);
1032}
1033
1034static void iolatency_pd_free(struct blkg_policy_data *pd)
1035{
1036	struct iolatency_grp *iolat = pd_to_lat(pd);
1037	free_percpu(iolat->stats);
1038	kfree(iolat);
1039}
1040
1041static struct cftype iolatency_files[] = {
1042	{
1043		.name = "latency",
1044		.flags = CFTYPE_NOT_ON_ROOT,
1045		.seq_show = iolatency_print_limit,
1046		.write = iolatency_set_limit,
1047	},
1048	{}
1049};
1050
1051static struct blkcg_policy blkcg_policy_iolatency = {
1052	.dfl_cftypes	= iolatency_files,
1053	.pd_alloc_fn	= iolatency_pd_alloc,
1054	.pd_init_fn	= iolatency_pd_init,
1055	.pd_offline_fn	= iolatency_pd_offline,
1056	.pd_free_fn	= iolatency_pd_free,
1057	.pd_stat_fn	= iolatency_pd_stat,
1058};
1059
1060static int __init iolatency_init(void)
1061{
1062	return blkcg_policy_register(&blkcg_policy_iolatency);
1063}
1064
1065static void __exit iolatency_exit(void)
1066{
1067	blkcg_policy_unregister(&blkcg_policy_iolatency);
1068}
1069
1070module_init(iolatency_init);
1071module_exit(iolatency_exit);