Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1063 insertions, 0 deletions

diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
new file mode 100644
index 000000000..74511a060
--- /dev/null
+++ b/block/blk-iolatency.c
@@ -0,0 +1,1063 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Block rq-qos base io controller
+ *
+ * This works similar to wbt with a few exceptions
+ *
+ * - It's bio based, so the latency covers the whole block layer in addition to
+ *   the actual io.
+ * - We will throttle all IO that comes in here if we need to.
+ * - We use the mean latency over the 100ms window.  This is because writes can
+ *   be particularly fast, which could give us a false sense of the impact of
+ *   other workloads on our protected workload.
+ * - By default there's no throttling, we set the queue_depth to UINT_MAX so
+ *   that we can have as many outstanding bio's as we're allowed to.  Only at
+ *   throttle time do we pay attention to the actual queue depth.
+ *
+ * The hierarchy works like the cpu controller does, we track the latency at
+ * every configured node, and each configured node has it's own independent
+ * queue depth.  This means that we only care about our latency targets at the
+ * peer level.  Some group at the bottom of the hierarchy isn't going to affect
+ * a group at the end of some other path if we're only configred at leaf level.
+ *
+ * Consider the following
+ *
+ *                   root blkg
+ *             /                     \
+ *        fast (target=5ms)     slow (target=10ms)
+ *         /     \                  /        \
+ *       a        b          normal(15ms)   unloved
+ *
+ * "a" and "b" have no target, but their combined io under "fast" cannot exceed
+ * an average latency of 5ms.  If it does then we will throttle the "slow"
+ * group.  In the case of "normal", if it exceeds its 15ms target, we will
+ * throttle "unloved", but nobody else.
+ *
+ * In this example "fast", "slow", and "normal" will be the only groups actually
+ * accounting their io latencies.  We have to walk up the heirarchy to the root
+ * on every submit and complete so we can do the appropriate stat recording and
+ * adjust the queue depth of ourselves if needed.
+ *
+ * There are 2 ways we throttle IO.
+ *
+ * 1) Queue depth throttling.  As we throttle down we will adjust the maximum
+ * number of IO's we're allowed to have in flight.  This starts at (u64)-1 down
+ * to 1.  If the group is only ever submitting IO for itself then this is the
+ * only way we throttle.
+ *
+ * 2) Induced delay throttling.  This is for the case that a group is generating
+ * IO that has to be issued by the root cg to avoid priority inversion. So think
+ * REQ_META or REQ_SWAP.  If we are already at qd == 1 and we're getting a lot
+ * of work done for us on behalf of the root cg and are being asked to scale
+ * down more then we induce a latency at userspace return.  We accumulate the
+ * total amount of time we need to be punished by doing
+ *
+ * total_time += min_lat_nsec - actual_io_completion
+ *
+ * and then at throttle time will do
+ *
+ * throttle_time = min(total_time, NSEC_PER_SEC)
+ *
+ * This induced delay will throttle back the activity that is generating the
+ * root cg issued io's, wethere that's some metadata intensive operation or the
+ * group is using so much memory that it is pushing us into swap.
+ *
+ * Copyright (C) 2018 Josef Bacik
+ */
+#include <linux/kernel.h>
+#include <linux/blk_types.h>
+#include <linux/backing-dev.h>
+#include <linux/module.h>
+#include <linux/timer.h>
+#include <linux/memcontrol.h>
+#include <linux/sched/loadavg.h>
+#include <linux/sched/signal.h>
+#include <trace/events/block.h>
+#include <linux/blk-mq.h>
+#include "blk-rq-qos.h"
+#include "blk-stat.h"
+#include "blk.h"
+
+#define DEFAULT_SCALE_COOKIE 1000000U
+
+static struct blkcg_policy blkcg_policy_iolatency;
+struct iolatency_grp;
+
+struct blk_iolatency {
+	struct rq_qos rqos;
+	struct timer_list timer;
+
+	/*
+	 * ->enabled is the master enable switch gating the throttling logic and
+	 * inflight tracking. The number of cgroups which have iolat enabled is
+	 * tracked in ->enable_cnt, and ->enable is flipped on/off accordingly
+	 * from ->enable_work with the request_queue frozen. For details, See
+	 * blkiolatency_enable_work_fn().
+	 */
+	bool enabled;
+	atomic_t enable_cnt;
+	struct work_struct enable_work;
+};
+
+static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos)
+{
+	return container_of(rqos, struct blk_iolatency, rqos);
+}
+
+struct child_latency_info {
+	spinlock_t lock;
+
+	/* Last time we adjusted the scale of everybody. */
+	u64 last_scale_event;
+
+	/* The latency that we missed. */
+	u64 scale_lat;
+
+	/* Total io's from all of our children for the last summation. */
+	u64 nr_samples;
+
+	/* The guy who actually changed the latency numbers. */
+	struct iolatency_grp *scale_grp;
+
+	/* Cookie to tell if we need to scale up or down. */
+	atomic_t scale_cookie;
+};
+
+struct percentile_stats {
+	u64 total;
+	u64 missed;
+};
+
+struct latency_stat {
+	union {
+		struct percentile_stats ps;
+		struct blk_rq_stat rqs;
+	};
+};
+
+struct iolatency_grp {
+	struct blkg_policy_data pd;
+	struct latency_stat __percpu *stats;
+	struct latency_stat cur_stat;
+	struct blk_iolatency *blkiolat;
+	struct rq_depth rq_depth;
+	struct rq_wait rq_wait;
+	atomic64_t window_start;
+	atomic_t scale_cookie;
+	u64 min_lat_nsec;
+	u64 cur_win_nsec;
+
+	/* total running average of our io latency. */
+	u64 lat_avg;
+
+	/* Our current number of IO's for the last summation. */
+	u64 nr_samples;
+
+	bool ssd;
+	struct child_latency_info child_lat;
+};
+
+#define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC)
+#define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC
+/*
+ * These are the constants used to fake the fixed-point moving average
+ * calculation just like load average.  The call to calc_load() folds
+ * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg.  The sampling
+ * window size is bucketed to try to approximately calculate average
+ * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows
+ * elapse immediately.  Note, windows only elapse with IO activity.  Idle
+ * periods extend the most recent window.
+ */
+#define BLKIOLATENCY_NR_EXP_FACTORS 5
+#define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \
+				      (BLKIOLATENCY_NR_EXP_FACTORS - 1))
+static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = {
+	2045, // exp(1/600) - 600 samples
+	2039, // exp(1/240) - 240 samples
+	2031, // exp(1/120) - 120 samples
+	2023, // exp(1/80)  - 80 samples
+	2014, // exp(1/60)  - 60 samples
+};
+
+static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd)
+{
+	return pd ? container_of(pd, struct iolatency_grp, pd) : NULL;
+}
+
+static inline struct iolatency_grp *blkg_to_lat(struct blkcg_gq *blkg)
+{
+	return pd_to_lat(blkg_to_pd(blkg, &blkcg_policy_iolatency));
+}
+
+static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat)
+{
+	return pd_to_blkg(&iolat->pd);
+}
+
+static inline void latency_stat_init(struct iolatency_grp *iolat,
+				     struct latency_stat *stat)
+{
+	if (iolat->ssd) {
+		stat->ps.total = 0;
+		stat->ps.missed = 0;
+	} else
+		blk_rq_stat_init(&stat->rqs);
+}
+
+static inline void latency_stat_sum(struct iolatency_grp *iolat,
+				    struct latency_stat *sum,
+				    struct latency_stat *stat)
+{
+	if (iolat->ssd) {
+		sum->ps.total += stat->ps.total;
+		sum->ps.missed += stat->ps.missed;
+	} else
+		blk_rq_stat_sum(&sum->rqs, &stat->rqs);
+}
+
+static inline void latency_stat_record_time(struct iolatency_grp *iolat,
+					    u64 req_time)
+{
+	struct latency_stat *stat = get_cpu_ptr(iolat->stats);
+	if (iolat->ssd) {
+		if (req_time >= iolat->min_lat_nsec)
+			stat->ps.missed++;
+		stat->ps.total++;
+	} else
+		blk_rq_stat_add(&stat->rqs, req_time);
+	put_cpu_ptr(stat);
+}
+
+static inline bool latency_sum_ok(struct iolatency_grp *iolat,
+				  struct latency_stat *stat)
+{
+	if (iolat->ssd) {
+		u64 thresh = div64_u64(stat->ps.total, 10);
+		thresh = max(thresh, 1ULL);
+		return stat->ps.missed < thresh;
+	}
+	return stat->rqs.mean <= iolat->min_lat_nsec;
+}
+
+static inline u64 latency_stat_samples(struct iolatency_grp *iolat,
+				       struct latency_stat *stat)
+{
+	if (iolat->ssd)
+		return stat->ps.total;
+	return stat->rqs.nr_samples;
+}
+
+static inline void iolat_update_total_lat_avg(struct iolatency_grp *iolat,
+					      struct latency_stat *stat)
+{
+	int exp_idx;
+
+	if (iolat->ssd)
+		return;
+
+	/*
+	 * calc_load() takes in a number stored in fixed point representation.
+	 * Because we are using this for IO time in ns, the values stored
+	 * are significantly larger than the FIXED_1 denominator (2048).
+	 * Therefore, rounding errors in the calculation are negligible and
+	 * can be ignored.
+	 */
+	exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1,
+			div64_u64(iolat->cur_win_nsec,
+				  BLKIOLATENCY_EXP_BUCKET_SIZE));
+	iolat->lat_avg = calc_load(iolat->lat_avg,
+				   iolatency_exp_factors[exp_idx],
+				   stat->rqs.mean);
+}
+
+static void iolat_cleanup_cb(struct rq_wait *rqw, void *private_data)
+{
+	atomic_dec(&rqw->inflight);
+	wake_up(&rqw->wait);
+}
+
+static bool iolat_acquire_inflight(struct rq_wait *rqw, void *private_data)
+{
+	struct iolatency_grp *iolat = private_data;
+	return rq_wait_inc_below(rqw, iolat->rq_depth.max_depth);
+}
+
+static void __blkcg_iolatency_throttle(struct rq_qos *rqos,
+				       struct iolatency_grp *iolat,
+				       bool issue_as_root,
+				       bool use_memdelay)
+{
+	struct rq_wait *rqw = &iolat->rq_wait;
+	unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay);
+
+	if (use_delay)
+		blkcg_schedule_throttle(rqos->q, use_memdelay);
+
+	/*
+	 * To avoid priority inversions we want to just take a slot if we are
+	 * issuing as root.  If we're being killed off there's no point in
+	 * delaying things, we may have been killed by OOM so throttling may
+	 * make recovery take even longer, so just let the IO's through so the
+	 * task can go away.
+	 */
+	if (issue_as_root || fatal_signal_pending(current)) {
+		atomic_inc(&rqw->inflight);
+		return;
+	}
+
+	rq_qos_wait(rqw, iolat, iolat_acquire_inflight, iolat_cleanup_cb);
+}
+
+#define SCALE_DOWN_FACTOR 2
+#define SCALE_UP_FACTOR 4
+
+static inline unsigned long scale_amount(unsigned long qd, bool up)
+{
+	return max(up ? qd >> SCALE_UP_FACTOR : qd >> SCALE_DOWN_FACTOR, 1UL);
+}
+
+/*
+ * We scale the qd down faster than we scale up, so we need to use this helper
+ * to adjust the scale_cookie accordingly so we don't prematurely get
+ * scale_cookie at DEFAULT_SCALE_COOKIE and unthrottle too much.
+ *
+ * Each group has their own local copy of the last scale cookie they saw, so if
+ * the global scale cookie goes up or down they know which way they need to go
+ * based on their last knowledge of it.
+ */
+static void scale_cookie_change(struct blk_iolatency *blkiolat,
+				struct child_latency_info *lat_info,
+				bool up)
+{
+	unsigned long qd = blkiolat->rqos.q->nr_requests;
+	unsigned long scale = scale_amount(qd, up);
+	unsigned long old = atomic_read(&lat_info->scale_cookie);
+	unsigned long max_scale = qd << 1;
+	unsigned long diff = 0;
+
+	if (old < DEFAULT_SCALE_COOKIE)
+		diff = DEFAULT_SCALE_COOKIE - old;
+
+	if (up) {
+		if (scale + old > DEFAULT_SCALE_COOKIE)
+			atomic_set(&lat_info->scale_cookie,
+				   DEFAULT_SCALE_COOKIE);
+		else if (diff > qd)
+			atomic_inc(&lat_info->scale_cookie);
+		else
+			atomic_add(scale, &lat_info->scale_cookie);
+	} else {
+		/*
+		 * We don't want to dig a hole so deep that it takes us hours to
+		 * dig out of it.  Just enough that we don't throttle/unthrottle
+		 * with jagged workloads but can still unthrottle once pressure
+		 * has sufficiently dissipated.
+		 */
+		if (diff > qd) {
+			if (diff < max_scale)
+				atomic_dec(&lat_info->scale_cookie);
+		} else {
+			atomic_sub(scale, &lat_info->scale_cookie);
+		}
+	}
+}
+
+/*
+ * Change the queue depth of the iolatency_grp.  We add/subtract 1/16th of the
+ * queue depth at a time so we don't get wild swings and hopefully dial in to
+ * fairer distribution of the overall queue depth.
+ */
+static void scale_change(struct iolatency_grp *iolat, bool up)
+{
+	unsigned long qd = iolat->blkiolat->rqos.q->nr_requests;
+	unsigned long scale = scale_amount(qd, up);
+	unsigned long old = iolat->rq_depth.max_depth;
+
+	if (old > qd)
+		old = qd;
+
+	if (up) {
+		if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat)))
+			return;
+
+		if (old < qd) {
+			old += scale;
+			old = min(old, qd);
+			iolat->rq_depth.max_depth = old;
+			wake_up_all(&iolat->rq_wait.wait);
+		}
+	} else {
+		old >>= 1;
+		iolat->rq_depth.max_depth = max(old, 1UL);
+	}
+}
+
+/* Check our parent and see if the scale cookie has changed. */
+static void check_scale_change(struct iolatency_grp *iolat)
+{
+	struct iolatency_grp *parent;
+	struct child_latency_info *lat_info;
+	unsigned int cur_cookie;
+	unsigned int our_cookie = atomic_read(&iolat->scale_cookie);
+	u64 scale_lat;
+	unsigned int old;
+	int direction = 0;
+
+	if (lat_to_blkg(iolat)->parent == NULL)
+		return;
+
+	parent = blkg_to_lat(lat_to_blkg(iolat)->parent);
+	if (!parent)
+		return;
+
+	lat_info = &parent->child_lat;
+	cur_cookie = atomic_read(&lat_info->scale_cookie);
+	scale_lat = READ_ONCE(lat_info->scale_lat);
+
+	if (cur_cookie < our_cookie)
+		direction = -1;
+	else if (cur_cookie > our_cookie)
+		direction = 1;
+	else
+		return;
+
+	old = atomic_cmpxchg(&iolat->scale_cookie, our_cookie, cur_cookie);
+
+	/* Somebody beat us to the punch, just bail. */
+	if (old != our_cookie)
+		return;
+
+	if (direction < 0 && iolat->min_lat_nsec) {
+		u64 samples_thresh;
+
+		if (!scale_lat || iolat->min_lat_nsec <= scale_lat)
+			return;
+
+		/*
+		 * Sometimes high priority groups are their own worst enemy, so
+		 * instead of taking it out on some poor other group that did 5%
+		 * or less of the IO's for the last summation just skip this
+		 * scale down event.
+		 */
+		samples_thresh = lat_info->nr_samples * 5;
+		samples_thresh = max(1ULL, div64_u64(samples_thresh, 100));
+		if (iolat->nr_samples <= samples_thresh)
+			return;
+	}
+
+	/* We're as low as we can go. */
+	if (iolat->rq_depth.max_depth == 1 && direction < 0) {
+		blkcg_use_delay(lat_to_blkg(iolat));
+		return;
+	}
+
+	/* We're back to the default cookie, unthrottle all the things. */
+	if (cur_cookie == DEFAULT_SCALE_COOKIE) {
+		blkcg_clear_delay(lat_to_blkg(iolat));
+		iolat->rq_depth.max_depth = UINT_MAX;
+		wake_up_all(&iolat->rq_wait.wait);
+		return;
+	}
+
+	scale_change(iolat, direction > 0);
+}
+
+static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio)
+{
+	struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
+	struct blkcg_gq *blkg = bio->bi_blkg;
+	bool issue_as_root = bio_issue_as_root_blkg(bio);
+
+	if (!blkiolat->enabled)
+		return;
+
+	while (blkg && blkg->parent) {
+		struct iolatency_grp *iolat = blkg_to_lat(blkg);
+		if (!iolat) {
+			blkg = blkg->parent;
+			continue;
+		}
+
+		check_scale_change(iolat);
+		__blkcg_iolatency_throttle(rqos, iolat, issue_as_root,
+				     (bio->bi_opf & REQ_SWAP) == REQ_SWAP);
+		blkg = blkg->parent;
+	}
+	if (!timer_pending(&blkiolat->timer))
+		mod_timer(&blkiolat->timer, jiffies + HZ);
+}
+
+static void iolatency_record_time(struct iolatency_grp *iolat,
+				  struct bio_issue *issue, u64 now,
+				  bool issue_as_root)
+{
+	u64 start = bio_issue_time(issue);
+	u64 req_time;
+
+	/*
+	 * Have to do this so we are truncated to the correct time that our
+	 * issue is truncated to.
+	 */
+	now = __bio_issue_time(now);
+
+	if (now <= start)
+		return;
+
+	req_time = now - start;
+
+	/*
+	 * We don't want to count issue_as_root bio's in the cgroups latency
+	 * statistics as it could skew the numbers downwards.
+	 */
+	if (unlikely(issue_as_root && iolat->rq_depth.max_depth != UINT_MAX)) {
+		u64 sub = iolat->min_lat_nsec;
+		if (req_time < sub)
+			blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time);
+		return;
+	}
+
+	latency_stat_record_time(iolat, req_time);
+}
+
+#define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC)
+#define BLKIOLATENCY_MIN_GOOD_SAMPLES 5
+
+static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now)
+{
+	struct blkcg_gq *blkg = lat_to_blkg(iolat);
+	struct iolatency_grp *parent;
+	struct child_latency_info *lat_info;
+	struct latency_stat stat;
+	unsigned long flags;
+	int cpu;
+
+	latency_stat_init(iolat, &stat);
+	preempt_disable();
+	for_each_online_cpu(cpu) {
+		struct latency_stat *s;
+		s = per_cpu_ptr(iolat->stats, cpu);
+		latency_stat_sum(iolat, &stat, s);
+		latency_stat_init(iolat, s);
+	}
+	preempt_enable();
+
+	parent = blkg_to_lat(blkg->parent);
+	if (!parent)
+		return;
+
+	lat_info = &parent->child_lat;
+
+	iolat_update_total_lat_avg(iolat, &stat);
+
+	/* Everything is ok and we don't need to adjust the scale. */
+	if (latency_sum_ok(iolat, &stat) &&
+	    atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE)
+		return;
+
+	/* Somebody beat us to the punch, just bail. */
+	spin_lock_irqsave(&lat_info->lock, flags);
+
+	latency_stat_sum(iolat, &iolat->cur_stat, &stat);
+	lat_info->nr_samples -= iolat->nr_samples;
+	lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat);
+	iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat);
+
+	if ((lat_info->last_scale_event >= now ||
+	    now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME))
+		goto out;
+
+	if (latency_sum_ok(iolat, &iolat->cur_stat) &&
+	    latency_sum_ok(iolat, &stat)) {
+		if (latency_stat_samples(iolat, &iolat->cur_stat) <
+		    BLKIOLATENCY_MIN_GOOD_SAMPLES)
+			goto out;
+		if (lat_info->scale_grp == iolat) {
+			lat_info->last_scale_event = now;
+			scale_cookie_change(iolat->blkiolat, lat_info, true);
+		}
+	} else if (lat_info->scale_lat == 0 ||
+		   lat_info->scale_lat >= iolat->min_lat_nsec) {
+		lat_info->last_scale_event = now;
+		if (!lat_info->scale_grp ||
+		    lat_info->scale_lat > iolat->min_lat_nsec) {
+			WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec);
+			lat_info->scale_grp = iolat;
+		}
+		scale_cookie_change(iolat->blkiolat, lat_info, false);
+	}
+	latency_stat_init(iolat, &iolat->cur_stat);
+out:
+	spin_unlock_irqrestore(&lat_info->lock, flags);
+}
+
+static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio)
+{
+	struct blkcg_gq *blkg;
+	struct rq_wait *rqw;
+	struct iolatency_grp *iolat;
+	u64 window_start;
+	u64 now;
+	bool issue_as_root = bio_issue_as_root_blkg(bio);
+	int inflight = 0;
+
+	blkg = bio->bi_blkg;
+	if (!blkg || !bio_flagged(bio, BIO_TRACKED))
+		return;
+
+	iolat = blkg_to_lat(bio->bi_blkg);
+	if (!iolat)
+		return;
+
+	if (!iolat->blkiolat->enabled)
+		return;
+
+	now = ktime_to_ns(ktime_get());
+	while (blkg && blkg->parent) {
+		iolat = blkg_to_lat(blkg);
+		if (!iolat) {
+			blkg = blkg->parent;
+			continue;
+		}
+		rqw = &iolat->rq_wait;
+
+		inflight = atomic_dec_return(&rqw->inflight);
+		WARN_ON_ONCE(inflight < 0);
+		/*
+		 * If bi_status is BLK_STS_AGAIN, the bio wasn't actually
+		 * submitted, so do not account for it.
+		 */
+		if (iolat->min_lat_nsec && bio->bi_status != BLK_STS_AGAIN) {
+			iolatency_record_time(iolat, &bio->bi_issue, now,
+					      issue_as_root);
+			window_start = atomic64_read(&iolat->window_start);
+			if (now > window_start &&
+			    (now - window_start) >= iolat->cur_win_nsec) {
+				if (atomic64_cmpxchg(&iolat->window_start,
+					     window_start, now) == window_start)
+					iolatency_check_latencies(iolat, now);
+			}
+		}
+		wake_up(&rqw->wait);
+		blkg = blkg->parent;
+	}
+}
+
+static void blkcg_iolatency_exit(struct rq_qos *rqos)
+{
+	struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
+
+	del_timer_sync(&blkiolat->timer);
+	flush_work(&blkiolat->enable_work);
+	blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency);
+	kfree(blkiolat);
+}
+
+static struct rq_qos_ops blkcg_iolatency_ops = {
+	.throttle = blkcg_iolatency_throttle,
+	.done_bio = blkcg_iolatency_done_bio,
+	.exit = blkcg_iolatency_exit,
+};
+
+static void blkiolatency_timer_fn(struct timer_list *t)
+{
+	struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer);
+	struct blkcg_gq *blkg;
+	struct cgroup_subsys_state *pos_css;
+	u64 now = ktime_to_ns(ktime_get());
+
+	rcu_read_lock();
+	blkg_for_each_descendant_pre(blkg, pos_css,
+				     blkiolat->rqos.q->root_blkg) {
+		struct iolatency_grp *iolat;
+		struct child_latency_info *lat_info;
+		unsigned long flags;
+		u64 cookie;
+
+		/*
+		 * We could be exiting, don't access the pd unless we have a
+		 * ref on the blkg.
+		 */
+		if (!blkg_tryget(blkg))
+			continue;
+
+		iolat = blkg_to_lat(blkg);
+		if (!iolat)
+			goto next;
+
+		lat_info = &iolat->child_lat;
+		cookie = atomic_read(&lat_info->scale_cookie);
+
+		if (cookie >= DEFAULT_SCALE_COOKIE)
+			goto next;
+
+		spin_lock_irqsave(&lat_info->lock, flags);
+		if (lat_info->last_scale_event >= now)
+			goto next_lock;
+
+		/*
+		 * We scaled down but don't have a scale_grp, scale up and carry
+		 * on.
+		 */
+		if (lat_info->scale_grp == NULL) {
+			scale_cookie_change(iolat->blkiolat, lat_info, true);
+			goto next_lock;
+		}
+
+		/*
+		 * It's been 5 seconds since our last scale event, clear the
+		 * scale grp in case the group that needed the scale down isn't
+		 * doing any IO currently.
+		 */
+		if (now - lat_info->last_scale_event >=
+		    ((u64)NSEC_PER_SEC * 5))
+			lat_info->scale_grp = NULL;
+next_lock:
+		spin_unlock_irqrestore(&lat_info->lock, flags);
+next:
+		blkg_put(blkg);
+	}
+	rcu_read_unlock();
+}
+
+/**
+ * blkiolatency_enable_work_fn - Enable or disable iolatency on the device
+ * @work: enable_work of the blk_iolatency of interest
+ *
+ * iolatency needs to keep track of the number of in-flight IOs per cgroup. This
+ * is relatively expensive as it involves walking up the hierarchy twice for
+ * every IO. Thus, if iolatency is not enabled in any cgroup for the device, we
+ * want to disable the in-flight tracking.
+ *
+ * We have to make sure that the counting is balanced - we don't want to leak
+ * the in-flight counts by disabling accounting in the completion path while IOs
+ * are in flight. This is achieved by ensuring that no IO is in flight by
+ * freezing the queue while flipping ->enabled. As this requires a sleepable
+ * context, ->enabled flipping is punted to this work function.
+ */
+static void blkiolatency_enable_work_fn(struct work_struct *work)
+{
+	struct blk_iolatency *blkiolat = container_of(work, struct blk_iolatency,
+						      enable_work);
+	bool enabled;
+
+	/*
+	 * There can only be one instance of this function running for @blkiolat
+	 * and it's guaranteed to be executed at least once after the latest
+	 * ->enabled_cnt modification. Acting on the latest ->enable_cnt is
+	 * sufficient.
+	 *
+	 * Also, we know @blkiolat is safe to access as ->enable_work is flushed
+	 * in blkcg_iolatency_exit().
+	 */
+	enabled = atomic_read(&blkiolat->enable_cnt);
+	if (enabled != blkiolat->enabled) {
+		blk_mq_freeze_queue(blkiolat->rqos.q);
+		blkiolat->enabled = enabled;
+		blk_mq_unfreeze_queue(blkiolat->rqos.q);
+	}
+}
+
+int blk_iolatency_init(struct request_queue *q)
+{
+	struct blk_iolatency *blkiolat;
+	struct rq_qos *rqos;
+	int ret;
+
+	blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL);
+	if (!blkiolat)
+		return -ENOMEM;
+
+	rqos = &blkiolat->rqos;
+	rqos->id = RQ_QOS_LATENCY;
+	rqos->ops = &blkcg_iolatency_ops;
+	rqos->q = q;
+
+	rq_qos_add(q, rqos);
+
+	ret = blkcg_activate_policy(q, &blkcg_policy_iolatency);
+	if (ret) {
+		rq_qos_del(q, rqos);
+		kfree(blkiolat);
+		return ret;
+	}
+
+	timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0);
+	INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn);
+
+	return 0;
+}
+
+static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val)
+{
+	struct iolatency_grp *iolat = blkg_to_lat(blkg);
+	struct blk_iolatency *blkiolat = iolat->blkiolat;
+	u64 oldval = iolat->min_lat_nsec;
+
+	iolat->min_lat_nsec = val;
+	iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE);
+	iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec,
+				    BLKIOLATENCY_MAX_WIN_SIZE);
+
+	if (!oldval && val) {
+		if (atomic_inc_return(&blkiolat->enable_cnt) == 1)
+			schedule_work(&blkiolat->enable_work);
+	}
+	if (oldval && !val) {
+		blkcg_clear_delay(blkg);
+		if (atomic_dec_return(&blkiolat->enable_cnt) == 0)
+			schedule_work(&blkiolat->enable_work);
+	}
+}
+
+static void iolatency_clear_scaling(struct blkcg_gq *blkg)
+{
+	if (blkg->parent) {
+		struct iolatency_grp *iolat = blkg_to_lat(blkg->parent);
+		struct child_latency_info *lat_info;
+		if (!iolat)
+			return;
+
+		lat_info = &iolat->child_lat;
+		spin_lock(&lat_info->lock);
+		atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE);
+		lat_info->last_scale_event = 0;
+		lat_info->scale_grp = NULL;
+		lat_info->scale_lat = 0;
+		spin_unlock(&lat_info->lock);
+	}
+}
+
+static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf,
+			     size_t nbytes, loff_t off)
+{
+	struct blkcg *blkcg = css_to_blkcg(of_css(of));
+	struct blkcg_gq *blkg;
+	struct blkg_conf_ctx ctx;
+	struct iolatency_grp *iolat;
+	char *p, *tok;
+	u64 lat_val = 0;
+	u64 oldval;
+	int ret;
+
+	ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx);
+	if (ret)
+		return ret;
+
+	iolat = blkg_to_lat(ctx.blkg);
+	p = ctx.body;
+
+	ret = -EINVAL;
+	while ((tok = strsep(&p, " "))) {
+		char key[16];
+		char val[21];	/* 18446744073709551616 */
+
+		if (sscanf(tok, "%15[^=]=%20s", key, val) != 2)
+			goto out;
+
+		if (!strcmp(key, "target")) {
+			u64 v;
+
+			if (!strcmp(val, "max"))
+				lat_val = 0;
+			else if (sscanf(val, "%llu", &v) == 1)
+				lat_val = v * NSEC_PER_USEC;
+			else
+				goto out;
+		} else {
+			goto out;
+		}
+	}
+
+	/* Walk up the tree to see if our new val is lower than it should be. */
+	blkg = ctx.blkg;
+	oldval = iolat->min_lat_nsec;
+
+	iolatency_set_min_lat_nsec(blkg, lat_val);
+	if (oldval != iolat->min_lat_nsec)
+		iolatency_clear_scaling(blkg);
+	ret = 0;
+out:
+	blkg_conf_finish(&ctx);
+	return ret ?: nbytes;
+}
+
+static u64 iolatency_prfill_limit(struct seq_file *sf,
+				  struct blkg_policy_data *pd, int off)
+{
+	struct iolatency_grp *iolat = pd_to_lat(pd);
+	const char *dname = blkg_dev_name(pd->blkg);
+
+	if (!dname || !iolat->min_lat_nsec)
+		return 0;
+	seq_printf(sf, "%s target=%llu\n",
+		   dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC));
+	return 0;
+}
+
+static int iolatency_print_limit(struct seq_file *sf, void *v)
+{
+	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
+			  iolatency_prfill_limit,
+			  &blkcg_policy_iolatency, seq_cft(sf)->private, false);
+	return 0;
+}
+
+static size_t iolatency_ssd_stat(struct iolatency_grp *iolat, char *buf,
+				 size_t size)
+{
+	struct latency_stat stat;
+	int cpu;
+
+	latency_stat_init(iolat, &stat);
+	preempt_disable();
+	for_each_online_cpu(cpu) {
+		struct latency_stat *s;
+		s = per_cpu_ptr(iolat->stats, cpu);
+		latency_stat_sum(iolat, &stat, s);
+	}
+	preempt_enable();
+
+	if (iolat->rq_depth.max_depth == UINT_MAX)
+		return scnprintf(buf, size, " missed=%llu total=%llu depth=max",
+				 (unsigned long long)stat.ps.missed,
+				 (unsigned long long)stat.ps.total);
+	return scnprintf(buf, size, " missed=%llu total=%llu depth=%u",
+			 (unsigned long long)stat.ps.missed,
+			 (unsigned long long)stat.ps.total,
+			 iolat->rq_depth.max_depth);
+}
+
+static size_t iolatency_pd_stat(struct blkg_policy_data *pd, char *buf,
+				size_t size)
+{
+	struct iolatency_grp *iolat = pd_to_lat(pd);
+	unsigned long long avg_lat;
+	unsigned long long cur_win;
+
+	if (!blkcg_debug_stats)
+		return 0;
+
+	if (iolat->ssd)
+		return iolatency_ssd_stat(iolat, buf, size);
+
+	avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC);
+	cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC);
+	if (iolat->rq_depth.max_depth == UINT_MAX)
+		return scnprintf(buf, size, " depth=max avg_lat=%llu win=%llu",
+				 avg_lat, cur_win);
+
+	return scnprintf(buf, size, " depth=%u avg_lat=%llu win=%llu",
+			 iolat->rq_depth.max_depth, avg_lat, cur_win);
+}
+
+
+static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp,
+						   struct request_queue *q,
+						   struct blkcg *blkcg)
+{
+	struct iolatency_grp *iolat;
+
+	iolat = kzalloc_node(sizeof(*iolat), gfp, q->node);
+	if (!iolat)
+		return NULL;
+	iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat),
+				       __alignof__(struct latency_stat), gfp);
+	if (!iolat->stats) {
+		kfree(iolat);
+		return NULL;
+	}
+	return &iolat->pd;
+}
+
+static void iolatency_pd_init(struct blkg_policy_data *pd)
+{
+	struct iolatency_grp *iolat = pd_to_lat(pd);
+	struct blkcg_gq *blkg = lat_to_blkg(iolat);
+	struct rq_qos *rqos = blkcg_rq_qos(blkg->q);
+	struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
+	u64 now = ktime_to_ns(ktime_get());
+	int cpu;
+
+	if (blk_queue_nonrot(blkg->q))
+		iolat->ssd = true;
+	else
+		iolat->ssd = false;
+
+	for_each_possible_cpu(cpu) {
+		struct latency_stat *stat;
+		stat = per_cpu_ptr(iolat->stats, cpu);
+		latency_stat_init(iolat, stat);
+	}
+
+	latency_stat_init(iolat, &iolat->cur_stat);
+	rq_wait_init(&iolat->rq_wait);
+	spin_lock_init(&iolat->child_lat.lock);
+	iolat->rq_depth.queue_depth = blkg->q->nr_requests;
+	iolat->rq_depth.max_depth = UINT_MAX;
+	iolat->rq_depth.default_depth = iolat->rq_depth.queue_depth;
+	iolat->blkiolat = blkiolat;
+	iolat->cur_win_nsec = 100 * NSEC_PER_MSEC;
+	atomic64_set(&iolat->window_start, now);
+
+	/*
+	 * We init things in list order, so the pd for the parent may not be
+	 * init'ed yet for whatever reason.
+	 */
+	if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) {
+		struct iolatency_grp *parent = blkg_to_lat(blkg->parent);
+		atomic_set(&iolat->scale_cookie,
+			   atomic_read(&parent->child_lat.scale_cookie));
+	} else {
+		atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE);
+	}
+
+	atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE);
+}
+
+static void iolatency_pd_offline(struct blkg_policy_data *pd)
+{
+	struct iolatency_grp *iolat = pd_to_lat(pd);
+	struct blkcg_gq *blkg = lat_to_blkg(iolat);
+
+	iolatency_set_min_lat_nsec(blkg, 0);
+	iolatency_clear_scaling(blkg);
+}
+
+static void iolatency_pd_free(struct blkg_policy_data *pd)
+{
+	struct iolatency_grp *iolat = pd_to_lat(pd);
+	free_percpu(iolat->stats);
+	kfree(iolat);
+}
+
+static struct cftype iolatency_files[] = {
+	{
+		.name = "latency",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = iolatency_print_limit,
+		.write = iolatency_set_limit,
+	},
+	{}
+};
+
+static struct blkcg_policy blkcg_policy_iolatency = {
+	.dfl_cftypes	= iolatency_files,
+	.pd_alloc_fn	= iolatency_pd_alloc,
+	.pd_init_fn	= iolatency_pd_init,
+	.pd_offline_fn	= iolatency_pd_offline,
+	.pd_free_fn	= iolatency_pd_free,
+	.pd_stat_fn	= iolatency_pd_stat,
+};
+
+static int __init iolatency_init(void)
+{
+	return blkcg_policy_register(&blkcg_policy_iolatency);
+}
+
+static void __exit iolatency_exit(void)
+{
+	blkcg_policy_unregister(&blkcg_policy_iolatency);
+}
+
+module_init(iolatency_init);
+module_exit(iolatency_exit);