Quelle blk-iolatency.c Sprache: 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;
unsigned int max_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->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->disk, 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.disk->queue->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 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.  We halve the queue depth
* at a time so we can scale down queue depth quickly from default unlimited
* to target.
*/
static void scale_change(struct iolatency_grp *iolat, bool up)
{
unsigned long qd = iolat->blkiolat->rqos.disk->queue->nr_requests;
unsigned long scale = scale_amount(qd, up);
unsigned long old = iolat->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->max_depth = old;
   wake_up_all(&iolat->rq_wait.wait);
  }
} else {
  old >>= 1;
  iolat->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;
int direction = 0;

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;

if (!atomic_try_cmpxchg(&iolat->scale_cookie, &our_cookie, cur_cookie)) {
  /* Somebody beat us to the punch, just bail. */
  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->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->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, u64 start,
      u64 now, bool issue_as_root)
{
u64 req_time;

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->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 = blk_time_get_ns();
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->issue_time_ns, now,
           issue_as_root);
   window_start = atomic64_read(&iolat->window_start);
   if (now > window_start &&
       (now - window_start) >= iolat->cur_win_nsec) {
    if (atomic64_try_cmpxchg(&iolat->window_start,
        &window_start, now))
     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);

timer_shutdown_sync(&blkiolat->timer);
flush_work(&blkiolat->enable_work);
blkcg_deactivate_policy(rqos->disk, &blkcg_policy_iolatency);
kfree(blkiolat);
}

static const 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 = timer_container_of(blkiolat, t,
           timer);
struct blkcg_gq *blkg;
struct cgroup_subsys_state *pos_css;
u64 now = blk_time_get_ns();

rcu_read_lock();
blkg_for_each_descendant_pre(blkg, pos_css,
         blkiolat->rqos.disk->queue->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) {
  unsigned int memflags;

  memflags = blk_mq_freeze_queue(blkiolat->rqos.disk->queue);
  blkiolat->enabled = enabled;
  blk_mq_unfreeze_queue(blkiolat->rqos.disk->queue, memflags);
}
}

static int blk_iolatency_init(struct gendisk *disk)
{
struct blk_iolatency *blkiolat;
int ret;

blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL);
if (!blkiolat)
  return -ENOMEM;

ret = rq_qos_add(&blkiolat->rqos, disk, RQ_QOS_LATENCY,
    &blkcg_iolatency_ops);
if (ret)
  goto err_free;
ret = blkcg_activate_policy(disk, &blkcg_policy_iolatency);
if (ret)
  goto err_qos_del;

timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0);
INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn);

return 0;

err_qos_del:
rq_qos_del(&blkiolat->rqos);
err_free:
kfree(blkiolat);
return ret;
}

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;

blkg_conf_init(&ctx, buf);

ret = blkg_conf_open_bdev(&ctx);
if (ret)
  goto out;

/*
* blk_iolatency_init() may fail after rq_qos_add() succeeds which can
* confuse iolat_rq_qos() test. Make the test and init atomic.
*/
lockdep_assert_held(&ctx.bdev->bd_queue->rq_qos_mutex);
if (!iolat_rq_qos(ctx.bdev->bd_queue))
  ret = blk_iolatency_init(ctx.bdev->bd_disk);
if (ret)
  goto out;

ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, &ctx);
if (ret)
  goto out;

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_exit(&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->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->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->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->max_depth, avg_lat, cur_win);
}

static struct blkg_policy_data *iolatency_pd_alloc(struct gendisk *disk,
  struct blkcg *blkcg, gfp_t gfp)
{
struct iolatency_grp *iolat;

iolat = kzalloc_node(sizeof(*iolat), gfp, disk->node_id);
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 = iolat_rq_qos(blkg->q);
struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
u64 now = blk_time_get_ns();
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->max_depth = UINT_MAX;
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);

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