linux/block/blk-iolatency.c
Tejun Heo 8a177a36da blk-iolatency: Fix inflight count imbalances and IO hangs on offline
iolatency needs to track the number of inflight IOs per cgroup. As this
tracking can be expensive, it is disabled when no cgroup has iolatency
configured for the device. To ensure that the inflight counters stay
balanced, iolatency_set_limit() freezes the request_queue while manipulating
the enabled counter, which ensures that no IO is in flight and thus all
counters are zero.

Unfortunately, iolatency_set_limit() isn't the only place where the enabled
counter is manipulated. iolatency_pd_offline() can also dec the counter and
trigger disabling. As this disabling happens without freezing the q, this
can easily happen while some IOs are in flight and thus leak the counts.

This can be easily demonstrated by turning on iolatency on an one empty
cgroup while IOs are in flight in other cgroups and then removing the
cgroup. Note that iolatency shouldn't have been enabled elsewhere in the
system to ensure that removing the cgroup disables iolatency for the whole
device.

The following keeps flipping on and off iolatency on sda:

  echo +io > /sys/fs/cgroup/cgroup.subtree_control
  while true; do
      mkdir -p /sys/fs/cgroup/test
      echo '8:0 target=100000' > /sys/fs/cgroup/test/io.latency
      sleep 1
      rmdir /sys/fs/cgroup/test
      sleep 1
  done

and there's concurrent fio generating direct rand reads:

  fio --name test --filename=/dev/sda --direct=1 --rw=randread \
      --runtime=600 --time_based --iodepth=256 --numjobs=4 --bs=4k

while monitoring with the following drgn script:

  while True:
    for css in css_for_each_descendant_pre(prog['blkcg_root'].css.address_of_()):
        for pos in hlist_for_each(container_of(css, 'struct blkcg', 'css').blkg_list):
            blkg = container_of(pos, 'struct blkcg_gq', 'blkcg_node')
            pd = blkg.pd[prog['blkcg_policy_iolatency'].plid]
            if pd.value_() == 0:
                continue
            iolat = container_of(pd, 'struct iolatency_grp', 'pd')
            inflight = iolat.rq_wait.inflight.counter.value_()
            if inflight:
                print(f'inflight={inflight} {disk_name(blkg.q.disk).decode("utf-8")} '
                      f'{cgroup_path(css.cgroup).decode("utf-8")}')
    time.sleep(1)

The monitoring output looks like the following:

  inflight=1 sda /user.slice
  inflight=1 sda /user.slice
  ...
  inflight=14 sda /user.slice
  inflight=13 sda /user.slice
  inflight=17 sda /user.slice
  inflight=15 sda /user.slice
  inflight=18 sda /user.slice
  inflight=17 sda /user.slice
  inflight=20 sda /user.slice
  inflight=19 sda /user.slice <- fio stopped, inflight stuck at 19
  inflight=19 sda /user.slice
  inflight=19 sda /user.slice

If a cgroup with stuck inflight ends up getting throttled, the throttled IOs
will never get issued as there's no completion event to wake it up leading
to an indefinite hang.

This patch fixes the bug by unifying enable handling into a work item which
is automatically kicked off from iolatency_set_min_lat_nsec() which is
called from both iolatency_set_limit() and iolatency_pd_offline() paths.
Punting to a work item is necessary as iolatency_pd_offline() is called
under spinlocks while freezing a request_queue requires a sleepable context.

This also simplifies the code reducing LOC sans the comments and avoids the
unnecessary freezes which were happening whenever a cgroup's latency target
is newly set or cleared.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Liu Bo <bo.liu@linux.alibaba.com>
Fixes: 8c772a9bfc ("blk-iolatency: fix IO hang due to negative inflight counter")
Cc: stable@vger.kernel.org # v5.0+
Link: https://lore.kernel.org/r/Yn9ScX6Nx2qIiQQi@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-05-26 11:43:00 -06:00

1063 lines
29 KiB
C

// 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-cgroup.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_QOS_THROTTLED))
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 void iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s)
{
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)
seq_printf(s, " missed=%llu total=%llu depth=max",
(unsigned long long)stat.ps.missed,
(unsigned long long)stat.ps.total);
else
seq_printf(s, " missed=%llu total=%llu depth=%u",
(unsigned long long)stat.ps.missed,
(unsigned long long)stat.ps.total,
iolat->rq_depth.max_depth);
}
static void iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
{
struct iolatency_grp *iolat = pd_to_lat(pd);
unsigned long long avg_lat;
unsigned long long cur_win;
if (!blkcg_debug_stats)
return;
if (iolat->ssd)
return iolatency_ssd_stat(iolat, s);
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)
seq_printf(s, " depth=max avg_lat=%llu win=%llu",
avg_lat, cur_win);
else
seq_printf(s, " 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);