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    Subject[PATCH 7/8] blk-wbt: add general throttling mechanism
    Date
    We can hook this up to the block layer, to help throttle buffered
    writes.

    wbt registers a few trace points that can be used to track what is
    happening in the system:

    wbt_lat: 259:0: latency 2446318
    wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
    wmean=518866, wmin=15522, wmax=5330353, wsamples=57
    wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32

    This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
    dumps the current read/write stats for that window, and wbt_step shows a
    step down event where we now scale back writes. Each trace includes the
    device, 259:0 in this case.

    Signed-off-by: Jens Axboe <axboe@fb.com>
    ---
    block/Makefile | 1 +
    block/blk-wbt.c | 704 +++++++++++++++++++++++++++++++++++++++++++++
    block/blk-wbt.h | 166 +++++++++++
    include/trace/events/wbt.h | 153 ++++++++++
    4 files changed, 1024 insertions(+)
    create mode 100644 block/blk-wbt.c
    create mode 100644 block/blk-wbt.h
    create mode 100644 include/trace/events/wbt.h

    diff --git a/block/Makefile b/block/Makefile
    index 2528c596f7ec..a827f988c4e6 100644
    --- a/block/Makefile
    +++ b/block/Makefile
    @@ -24,3 +24,4 @@ obj-$(CONFIG_BLK_CMDLINE_PARSER) += cmdline-parser.o
    obj-$(CONFIG_BLK_DEV_INTEGRITY) += bio-integrity.o blk-integrity.o t10-pi.o
    obj-$(CONFIG_BLK_MQ_PCI) += blk-mq-pci.o
    obj-$(CONFIG_BLK_DEV_ZONED) += blk-zoned.o
    +obj-$(CONFIG_BLK_WBT) += blk-wbt.o
    diff --git a/block/blk-wbt.c b/block/blk-wbt.c
    new file mode 100644
    index 000000000000..1b1d67aae1d3
    --- /dev/null
    +++ b/block/blk-wbt.c
    @@ -0,0 +1,704 @@
    +/*
    + * buffered writeback throttling. loosely based on CoDel. We can't drop
    + * packets for IO scheduling, so the logic is something like this:
    + *
    + * - Monitor latencies in a defined window of time.
    + * - If the minimum latency in the above window exceeds some target, increment
    + * scaling step and scale down queue depth by a factor of 2x. The monitoring
    + * window is then shrunk to 100 / sqrt(scaling step + 1).
    + * - For any window where we don't have solid data on what the latencies
    + * look like, retain status quo.
    + * - If latencies look good, decrement scaling step.
    + * - If we're only doing writes, allow the scaling step to go negative. This
    + * will temporarily boost write performance, snapping back to a stable
    + * scaling step of 0 if reads show up or the heavy writers finish. Unlike
    + * positive scaling steps where we shrink the monitoring window, a negative
    + * scaling step retains the default step==0 window size.
    + *
    + * Copyright (C) 2016 Jens Axboe
    + *
    + */
    +#include <linux/kernel.h>
    +#include <linux/blk_types.h>
    +#include <linux/slab.h>
    +#include <linux/backing-dev.h>
    +#include <linux/swap.h>
    +
    +#include "blk-wbt.h"
    +
    +#define CREATE_TRACE_POINTS
    +#include <trace/events/wbt.h>
    +
    +enum {
    + /*
    + * Default setting, we'll scale up (to 75% of QD max) or down (min 1)
    + * from here depending on device stats
    + */
    + RWB_DEF_DEPTH = 16,
    +
    + /*
    + * 100msec window
    + */
    + RWB_WINDOW_NSEC = 100 * 1000 * 1000ULL,
    +
    + /*
    + * Disregard stats, if we don't meet this minimum
    + */
    + RWB_MIN_WRITE_SAMPLES = 3,
    +
    + /*
    + * If we have this number of consecutive windows with not enough
    + * information to scale up or down, scale up.
    + */
    + RWB_UNKNOWN_BUMP = 5,
    +};
    +
    +static inline bool rwb_enabled(struct rq_wb *rwb)
    +{
    + return rwb && rwb->wb_normal != 0;
    +}
    +
    +/*
    + * Increment 'v', if 'v' is below 'below'. Returns true if we succeeded,
    + * false if 'v' + 1 would be bigger than 'below'.
    + */
    +static bool atomic_inc_below(atomic_t *v, int below)
    +{
    + int cur = atomic_read(v);
    +
    + for (;;) {
    + int old;
    +
    + if (cur >= below)
    + return false;
    + old = atomic_cmpxchg(v, cur, cur + 1);
    + if (old == cur)
    + break;
    + cur = old;
    + }
    +
    + return true;
    +}
    +
    +static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
    +{
    + if (rwb_enabled(rwb)) {
    + const unsigned long cur = jiffies;
    +
    + if (cur != *var)
    + *var = cur;
    + }
    +}
    +
    +/*
    + * If a task was rate throttled in balance_dirty_pages() within the last
    + * second or so, use that to indicate a higher cleaning rate.
    + */
    +static bool wb_recent_wait(struct rq_wb *rwb)
    +{
    + struct bdi_writeback *wb = &rwb->bdi->wb;
    +
    + return time_before(jiffies, wb->dirty_sleep + HZ);
    +}
    +
    +static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, bool is_kswapd)
    +{
    + return &rwb->rq_wait[is_kswapd];
    +}
    +
    +static void rwb_wake_all(struct rq_wb *rwb)
    +{
    + int i;
    +
    + for (i = 0; i < WBT_NUM_RWQ; i++) {
    + struct rq_wait *rqw = &rwb->rq_wait[i];
    +
    + if (waitqueue_active(&rqw->wait))
    + wake_up_all(&rqw->wait);
    + }
    +}
    +
    +void __wbt_done(struct rq_wb *rwb, enum wbt_flags wb_acct)
    +{
    + struct rq_wait *rqw;
    + int inflight, limit;
    +
    + if (!(wb_acct & WBT_TRACKED))
    + return;
    +
    + rqw = get_rq_wait(rwb, wb_acct & WBT_KSWAPD);
    + inflight = atomic_dec_return(&rqw->inflight);
    +
    + /*
    + * wbt got disabled with IO in flight. Wake up any potential
    + * waiters, we don't have to do more than that.
    + */
    + if (unlikely(!rwb_enabled(rwb))) {
    + rwb_wake_all(rwb);
    + return;
    + }
    +
    + /*
    + * If the device does write back caching, drop further down
    + * before we wake people up.
    + */
    + if (rwb->wc && !wb_recent_wait(rwb))
    + limit = 0;
    + else
    + limit = rwb->wb_normal;
    +
    + /*
    + * Don't wake anyone up if we are above the normal limit.
    + */
    + if (inflight && inflight >= limit)
    + return;
    +
    + if (waitqueue_active(&rqw->wait)) {
    + int diff = limit - inflight;
    +
    + if (!inflight || diff >= rwb->wb_background / 2)
    + wake_up(&rqw->wait);
    + }
    +}
    +
    +/*
    + * Called on completion of a request. Note that it's also called when
    + * a request is merged, when the request gets freed.
    + */
    +void wbt_done(struct rq_wb *rwb, struct blk_issue_stat *stat)
    +{
    + if (!rwb)
    + return;
    +
    + if (!wbt_is_tracked(stat)) {
    + if (rwb->sync_cookie == stat) {
    + rwb->sync_issue = 0;
    + rwb->sync_cookie = NULL;
    + }
    +
    + if (wbt_is_read(stat))
    + wb_timestamp(rwb, &rwb->last_comp);
    + wbt_clear_state(stat);
    + } else {
    + WARN_ON_ONCE(stat == rwb->sync_cookie);
    + __wbt_done(rwb, wbt_stat_to_mask(stat));
    + wbt_clear_state(stat);
    + }
    +}
    +
    +/*
    + * Return true, if we can't increase the depth further by scaling
    + */
    +static bool calc_wb_limits(struct rq_wb *rwb)
    +{
    + unsigned int depth;
    + bool ret = false;
    +
    + if (!rwb->min_lat_nsec) {
    + rwb->wb_max = rwb->wb_normal = rwb->wb_background = 0;
    + return false;
    + }
    +
    + /*
    + * For QD=1 devices, this is a special case. It's important for those
    + * to have one request ready when one completes, so force a depth of
    + * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
    + * since the device can't have more than that in flight. If we're
    + * scaling down, then keep a setting of 1/1/1.
    + */
    + if (rwb->queue_depth == 1) {
    + if (rwb->scale_step > 0)
    + rwb->wb_max = rwb->wb_normal = 1;
    + else {
    + rwb->wb_max = rwb->wb_normal = 2;
    + ret = true;
    + }
    + rwb->wb_background = 1;
    + } else {
    + /*
    + * scale_step == 0 is our default state. If we have suffered
    + * latency spikes, step will be > 0, and we shrink the
    + * allowed write depths. If step is < 0, we're only doing
    + * writes, and we allow a temporarily higher depth to
    + * increase performance.
    + */
    + depth = min_t(unsigned int, RWB_DEF_DEPTH, rwb->queue_depth);
    + if (rwb->scale_step > 0)
    + depth = 1 + ((depth - 1) >> min(31, rwb->scale_step));
    + else if (rwb->scale_step < 0) {
    + unsigned int maxd = 3 * rwb->queue_depth / 4;
    +
    + depth = 1 + ((depth - 1) << -rwb->scale_step);
    + if (depth > maxd) {
    + depth = maxd;
    + ret = true;
    + }
    + }
    +
    + /*
    + * Set our max/normal/bg queue depths based on how far
    + * we have scaled down (->scale_step).
    + */
    + rwb->wb_max = depth;
    + rwb->wb_normal = (rwb->wb_max + 1) / 2;
    + rwb->wb_background = (rwb->wb_max + 3) / 4;
    + }
    +
    + return ret;
    +}
    +
    +static bool inline stat_sample_valid(struct blk_rq_stat *stat)
    +{
    + /*
    + * We need at least one read sample, and a minimum of
    + * RWB_MIN_WRITE_SAMPLES. We require some write samples to know
    + * that it's writes impacting us, and not just some sole read on
    + * a device that is in a lower power state.
    + */
    + return stat[0].nr_samples >= 1 &&
    + stat[1].nr_samples >= RWB_MIN_WRITE_SAMPLES;
    +}
    +
    +static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
    +{
    + u64 now, issue = ACCESS_ONCE(rwb->sync_issue);
    +
    + if (!issue || !rwb->sync_cookie)
    + return 0;
    +
    + now = ktime_to_ns(ktime_get());
    + return now - issue;
    +}
    +
    +enum {
    + LAT_OK = 1,
    + LAT_UNKNOWN,
    + LAT_UNKNOWN_WRITES,
    + LAT_EXCEEDED,
    +};
    +
    +static int __latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
    +{
    + u64 thislat;
    +
    + /*
    + * If our stored sync issue exceeds the window size, or it
    + * exceeds our min target AND we haven't logged any entries,
    + * flag the latency as exceeded. wbt works off completion latencies,
    + * but for a flooded device, a single sync IO can take a long time
    + * to complete after being issued. If this time exceeds our
    + * monitoring window AND we didn't see any other completions in that
    + * window, then count that sync IO as a violation of the latency.
    + */
    + thislat = rwb_sync_issue_lat(rwb);
    + if (thislat > rwb->cur_win_nsec ||
    + (thislat > rwb->min_lat_nsec && !stat[0].nr_samples)) {
    + trace_wbt_lat(rwb->bdi, thislat);
    + return LAT_EXCEEDED;
    + }
    +
    + /*
    + * No read/write mix, if stat isn't valid
    + */
    + if (!stat_sample_valid(stat)) {
    + /*
    + * If we had writes in this stat window and the window is
    + * current, we're only doing writes. If a task recently
    + * waited or still has writes in flights, consider us doing
    + * just writes as well.
    + */
    + if ((stat[1].nr_samples && rwb->stat_ops->is_current(stat)) ||
    + wb_recent_wait(rwb) || wbt_inflight(rwb))
    + return LAT_UNKNOWN_WRITES;
    + return LAT_UNKNOWN;
    + }
    +
    + /*
    + * If the 'min' latency exceeds our target, step down.
    + */
    + if (stat[0].min > rwb->min_lat_nsec) {
    + trace_wbt_lat(rwb->bdi, stat[0].min);
    + trace_wbt_stat(rwb->bdi, stat);
    + return LAT_EXCEEDED;
    + }
    +
    + if (rwb->scale_step)
    + trace_wbt_stat(rwb->bdi, stat);
    +
    + return LAT_OK;
    +}
    +
    +static int latency_exceeded(struct rq_wb *rwb)
    +{
    + struct blk_rq_stat stat[2];
    +
    + rwb->stat_ops->get(rwb->ops_data, stat);
    + return __latency_exceeded(rwb, stat);
    +}
    +
    +static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
    +{
    + trace_wbt_step(rwb->bdi, msg, rwb->scale_step, rwb->cur_win_nsec,
    + rwb->wb_background, rwb->wb_normal, rwb->wb_max);
    +}
    +
    +static void scale_up(struct rq_wb *rwb)
    +{
    + /*
    + * Hit max in previous round, stop here
    + */
    + if (rwb->scaled_max)
    + return;
    +
    + rwb->scale_step--;
    + rwb->unknown_cnt = 0;
    + rwb->stat_ops->clear(rwb->ops_data);
    +
    + rwb->scaled_max = calc_wb_limits(rwb);
    +
    + rwb_wake_all(rwb);
    +
    + rwb_trace_step(rwb, "step up");
    +}
    +
    +/*
    + * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
    + * had a latency violation.
    + */
    +static void scale_down(struct rq_wb *rwb, bool hard_throttle)
    +{
    + /*
    + * Stop scaling down when we've hit the limit. This also prevents
    + * ->scale_step from going to crazy values, if the device can't
    + * keep up.
    + */
    + if (rwb->wb_max == 1)
    + return;
    +
    + if (rwb->scale_step < 0 && hard_throttle)
    + rwb->scale_step = 0;
    + else
    + rwb->scale_step++;
    +
    + rwb->scaled_max = false;
    + rwb->unknown_cnt = 0;
    + rwb->stat_ops->clear(rwb->ops_data);
    + calc_wb_limits(rwb);
    + rwb_trace_step(rwb, "step down");
    +}
    +
    +static void rwb_arm_timer(struct rq_wb *rwb)
    +{
    + unsigned long expires;
    +
    + if (rwb->scale_step > 0) {
    + /*
    + * We should speed this up, using some variant of a fast
    + * integer inverse square root calculation. Since we only do
    + * this for every window expiration, it's not a huge deal,
    + * though.
    + */
    + rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,
    + int_sqrt((rwb->scale_step + 1) << 8));
    + } else {
    + /*
    + * For step < 0, we don't want to increase/decrease the
    + * window size.
    + */
    + rwb->cur_win_nsec = rwb->win_nsec;
    + }
    +
    + expires = jiffies + nsecs_to_jiffies(rwb->cur_win_nsec);
    + mod_timer(&rwb->window_timer, expires);
    +}
    +
    +static void wb_timer_fn(unsigned long data)
    +{
    + struct rq_wb *rwb = (struct rq_wb *) data;
    + unsigned int inflight = wbt_inflight(rwb);
    + int status;
    +
    + status = latency_exceeded(rwb);
    +
    + trace_wbt_timer(rwb->bdi, status, rwb->scale_step, inflight);
    +
    + /*
    + * If we exceeded the latency target, step down. If we did not,
    + * step one level up. If we don't know enough to say either exceeded
    + * or ok, then don't do anything.
    + */
    + switch (status) {
    + case LAT_EXCEEDED:
    + scale_down(rwb, true);
    + break;
    + case LAT_OK:
    + scale_up(rwb);
    + break;
    + case LAT_UNKNOWN_WRITES:
    + scale_up(rwb);
    + break;
    + case LAT_UNKNOWN:
    + if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
    + break;
    + /*
    + * We get here for two reasons:
    + *
    + * 1) We previously scaled reduced depth, and we currently
    + * don't have a valid read/write sample. For that case,
    + * slowly return to center state (step == 0).
    + * 2) We started a the center step, but don't have a valid
    + * read/write sample, but we do have writes going on.
    + * Allow step to go negative, to increase write perf.
    + */
    + if (rwb->scale_step > 0)
    + scale_up(rwb);
    + else if (rwb->scale_step < 0)
    + scale_down(rwb, false);
    + break;
    + default:
    + break;
    + }
    +
    + /*
    + * Re-arm timer, if we have IO in flight
    + */
    + if (rwb->scale_step || inflight)
    + rwb_arm_timer(rwb);
    +}
    +
    +void wbt_update_limits(struct rq_wb *rwb)
    +{
    + rwb->scale_step = 0;
    + rwb->scaled_max = false;
    + calc_wb_limits(rwb);
    +
    + rwb_wake_all(rwb);
    +}
    +
    +static bool close_io(struct rq_wb *rwb)
    +{
    + const unsigned long now = jiffies;
    +
    + return time_before(now, rwb->last_issue + HZ / 10) ||
    + time_before(now, rwb->last_comp + HZ / 10);
    +}
    +
    +#define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO)
    +
    +static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw)
    +{
    + unsigned int limit;
    +
    + /*
    + * At this point we know it's a buffered write. If this is
    + * kswapd trying to free memory, or REQ_SYNC is set, set, then
    + * it's WB_SYNC_ALL writeback, and we'll use the max limit for
    + * that. If the write is marked as a background write, then use
    + * the idle limit, or go to normal if we haven't had competing
    + * IO for a bit.
    + */
    + if ((rw & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd())
    + limit = rwb->wb_max;
    + else if ((rw & REQ_BACKGROUND) || close_io(rwb)) {
    + /*
    + * If less than 100ms since we completed unrelated IO,
    + * limit us to half the depth for background writeback.
    + */
    + limit = rwb->wb_background;
    + } else
    + limit = rwb->wb_normal;
    +
    + return limit;
    +}
    +
    +static inline bool may_queue(struct rq_wb *rwb, struct rq_wait *rqw,
    + unsigned long rw)
    +{
    + /*
    + * inc it here even if disabled, since we'll dec it at completion.
    + * this only happens if the task was sleeping in __wbt_wait(),
    + * and someone turned it off at the same time.
    + */
    + if (!rwb_enabled(rwb)) {
    + atomic_inc(&rqw->inflight);
    + return true;
    + }
    +
    + return atomic_inc_below(&rqw->inflight, get_limit(rwb, rw));
    +}
    +
    +/*
    + * Block if we will exceed our limit, or if we are currently waiting for
    + * the timer to kick off queuing again.
    + */
    +static void __wbt_wait(struct rq_wb *rwb, unsigned long rw, spinlock_t *lock)
    +{
    + struct rq_wait *rqw = get_rq_wait(rwb, current_is_kswapd());
    + DEFINE_WAIT(wait);
    +
    + if (may_queue(rwb, rqw, rw))
    + return;
    +
    + do {
    + prepare_to_wait_exclusive(&rqw->wait, &wait,
    + TASK_UNINTERRUPTIBLE);
    +
    + if (may_queue(rwb, rqw, rw))
    + break;
    +
    + if (lock)
    + spin_unlock_irq(lock);
    +
    + io_schedule();
    +
    + if (lock)
    + spin_lock_irq(lock);
    + } while (1);
    +
    + finish_wait(&rqw->wait, &wait);
    +}
    +
    +static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio)
    +{
    + const int op = bio_op(bio);
    +
    + /*
    + * If not a WRITE (or a discard), do nothing
    + */
    + if (!(op == REQ_OP_WRITE || op == REQ_OP_DISCARD))
    + return false;
    +
    + /*
    + * Don't throttle WRITE_ODIRECT
    + */
    + if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE))
    + return false;
    +
    + return true;
    +}
    +
    +/*
    + * Returns true if the IO request should be accounted, false if not.
    + * May sleep, if we have exceeded the writeback limits. Caller can pass
    + * in an irq held spinlock, if it holds one when calling this function.
    + * If we do sleep, we'll release and re-grab it.
    + */
    +unsigned int wbt_wait(struct rq_wb *rwb, struct bio *bio, spinlock_t *lock)
    +{
    + unsigned int ret = 0;
    +
    + if (!rwb_enabled(rwb))
    + return 0;
    +
    + if (bio_op(bio) == REQ_OP_READ)
    + ret = WBT_READ;
    +
    + if (!wbt_should_throttle(rwb, bio)) {
    + if (ret & WBT_READ)
    + wb_timestamp(rwb, &rwb->last_issue);
    + return ret;
    + }
    +
    + __wbt_wait(rwb, bio->bi_opf, lock);
    +
    + if (!timer_pending(&rwb->window_timer))
    + rwb_arm_timer(rwb);
    +
    + if (current_is_kswapd())
    + ret |= WBT_KSWAPD;
    +
    + return ret | WBT_TRACKED;
    +}
    +
    +void wbt_issue(struct rq_wb *rwb, struct blk_issue_stat *stat)
    +{
    + if (!rwb_enabled(rwb))
    + return;
    +
    + /*
    + * Track sync issue, in case it takes a long time to complete. Allows
    + * us to react quicker, if a sync IO takes a long time to complete.
    + * Note that this is just a hint. 'stat' can go away when the
    + * request completes, so it's important we never dereference it. We
    + * only use the address to compare with, which is why we store the
    + * sync_issue time locally.
    + */
    + if (wbt_is_read(stat) && !rwb->sync_issue) {
    + rwb->sync_cookie = stat;
    + rwb->sync_issue = blk_stat_time(stat);
    + }
    +}
    +
    +void wbt_requeue(struct rq_wb *rwb, struct blk_issue_stat *stat)
    +{
    + if (!rwb_enabled(rwb))
    + return;
    + if (stat == rwb->sync_cookie) {
    + rwb->sync_issue = 0;
    + rwb->sync_cookie = NULL;
    + }
    +}
    +
    +void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth)
    +{
    + if (rwb) {
    + rwb->queue_depth = depth;
    + wbt_update_limits(rwb);
    + }
    +}
    +
    +void wbt_set_write_cache(struct rq_wb *rwb, bool write_cache_on)
    +{
    + if (rwb)
    + rwb->wc = write_cache_on;
    +}
    +
    +void wbt_disable(struct rq_wb *rwb)
    +{
    + if (rwb) {
    + del_timer_sync(&rwb->window_timer);
    + rwb->win_nsec = rwb->min_lat_nsec = 0;
    + wbt_update_limits(rwb);
    + }
    +}
    +EXPORT_SYMBOL_GPL(wbt_disable);
    +
    +struct rq_wb *wbt_init(struct backing_dev_info *bdi, struct wb_stat_ops *ops,
    + void *ops_data)
    +{
    + struct rq_wb *rwb;
    + int i;
    +
    + BUILD_BUG_ON(WBT_NR_BITS > BLK_STAT_RES_BITS);
    +
    + if (!ops->get || !ops->is_current || !ops->clear)
    + return ERR_PTR(-EINVAL);
    +
    + rwb = kzalloc(sizeof(*rwb), GFP_KERNEL);
    + if (!rwb)
    + return ERR_PTR(-ENOMEM);
    +
    + for (i = 0; i < WBT_NUM_RWQ; i++) {
    + atomic_set(&rwb->rq_wait[i].inflight, 0);
    + init_waitqueue_head(&rwb->rq_wait[i].wait);
    + }
    +
    + setup_timer(&rwb->window_timer, wb_timer_fn, (unsigned long) rwb);
    + rwb->wc = 1;
    + rwb->queue_depth = RWB_DEF_DEPTH;
    + rwb->last_comp = rwb->last_issue = jiffies;
    + rwb->bdi = bdi;
    + rwb->win_nsec = RWB_WINDOW_NSEC;
    + rwb->stat_ops = ops;
    + rwb->ops_data = ops_data;
    + wbt_update_limits(rwb);
    + return rwb;
    +}
    +
    +void wbt_exit(struct rq_wb *rwb)
    +{
    + if (rwb) {
    + del_timer_sync(&rwb->window_timer);
    + kfree(rwb);
    + }
    +}
    diff --git a/block/blk-wbt.h b/block/blk-wbt.h
    new file mode 100644
    index 000000000000..784e392b20e1
    --- /dev/null
    +++ b/block/blk-wbt.h
    @@ -0,0 +1,166 @@
    +#ifndef WB_THROTTLE_H
    +#define WB_THROTTLE_H
    +
    +#include <linux/kernel.h>
    +#include <linux/atomic.h>
    +#include <linux/wait.h>
    +#include <linux/timer.h>
    +#include <linux/ktime.h>
    +
    +#include "blk-stat.h"
    +
    +enum wbt_flags {
    + WBT_TRACKED = 1, /* write, tracked for throttling */
    + WBT_READ = 2, /* read */
    + WBT_KSWAPD = 4, /* write, from kswapd */
    +
    + WBT_NR_BITS = 3, /* number of bits */
    +};
    +
    +enum {
    + WBT_NUM_RWQ = 2,
    +};
    +
    +static inline void wbt_clear_state(struct blk_issue_stat *stat)
    +{
    + stat->time &= BLK_STAT_TIME_MASK;
    +}
    +
    +static inline enum wbt_flags wbt_stat_to_mask(struct blk_issue_stat *stat)
    +{
    + return (stat->time & BLK_STAT_MASK) >> BLK_STAT_SHIFT;
    +}
    +
    +static inline void wbt_track(struct blk_issue_stat *stat, enum wbt_flags wb_acct)
    +{
    + stat->time |= ((u64) wb_acct) << BLK_STAT_SHIFT;
    +}
    +
    +static inline bool wbt_is_tracked(struct blk_issue_stat *stat)
    +{
    + return (stat->time >> BLK_STAT_SHIFT) & WBT_TRACKED;
    +}
    +
    +static inline bool wbt_is_read(struct blk_issue_stat *stat)
    +{
    + return (stat->time >> BLK_STAT_SHIFT) & WBT_READ;
    +}
    +
    +struct wb_stat_ops {
    + void (*get)(void *, struct blk_rq_stat *);
    + bool (*is_current)(struct blk_rq_stat *);
    + void (*clear)(void *);
    +};
    +
    +struct rq_wait {
    + wait_queue_head_t wait;
    + atomic_t inflight;
    +};
    +
    +struct rq_wb {
    + /*
    + * Settings that govern how we throttle
    + */
    + unsigned int wb_background; /* background writeback */
    + unsigned int wb_normal; /* normal writeback */
    + unsigned int wb_max; /* max throughput writeback */
    + int scale_step;
    + bool scaled_max;
    +
    + /*
    + * Number of consecutive periods where we don't have enough
    + * information to make a firm scale up/down decision.
    + */
    + unsigned int unknown_cnt;
    +
    + u64 win_nsec; /* default window size */
    + u64 cur_win_nsec; /* current window size */
    +
    + struct timer_list window_timer;
    +
    + s64 sync_issue;
    + void *sync_cookie;
    +
    + unsigned int wc;
    + unsigned int queue_depth;
    +
    + unsigned long last_issue; /* last non-throttled issue */
    + unsigned long last_comp; /* last non-throttled comp */
    + unsigned long min_lat_nsec;
    + struct backing_dev_info *bdi;
    + struct rq_wait rq_wait[WBT_NUM_RWQ];
    +
    + struct wb_stat_ops *stat_ops;
    + void *ops_data;
    +};
    +
    +static inline unsigned int wbt_inflight(struct rq_wb *rwb)
    +{
    + unsigned int i, ret = 0;
    +
    + for (i = 0; i < WBT_NUM_RWQ; i++)
    + ret += atomic_read(&rwb->rq_wait[i].inflight);
    +
    + return ret;
    +}
    +
    +struct backing_dev_info;
    +
    +#ifdef CONFIG_BLK_WBT
    +
    +void __wbt_done(struct rq_wb *, enum wbt_flags);
    +void wbt_done(struct rq_wb *, struct blk_issue_stat *);
    +enum wbt_flags wbt_wait(struct rq_wb *, struct bio *, spinlock_t *);
    +struct rq_wb *wbt_init(struct backing_dev_info *, struct wb_stat_ops *, void *);
    +void wbt_exit(struct rq_wb *);
    +void wbt_update_limits(struct rq_wb *);
    +void wbt_requeue(struct rq_wb *, struct blk_issue_stat *);
    +void wbt_issue(struct rq_wb *, struct blk_issue_stat *);
    +void wbt_disable(struct rq_wb *);
    +
    +void wbt_set_queue_depth(struct rq_wb *, unsigned int);
    +void wbt_set_write_cache(struct rq_wb *, bool);
    +
    +#else
    +
    +static inline void __wbt_done(struct rq_wb *rwb, enum wbt_flags flags)
    +{
    +}
    +static inline void wbt_done(struct rq_wb *rwb, struct blk_issue_stat *stat)
    +{
    +}
    +static inline enum wbt_flags wbt_wait(struct rq_wb *rwb, struct bio *bio,
    + spinlock_t *lock)
    +{
    + return 0;
    +}
    +static inline struct rq_wb *wbt_init(struct backing_dev_info *bdi,
    + struct wb_stat_ops *ops, void *ops_data)
    +{
    + return ERR_PTR(-EINVAL);
    +}
    +static inline void wbt_exit(struct rq_wb *rbw)
    +{
    +}
    +static inline void wbt_update_limits(struct rq_wb *rwb)
    +{
    +}
    +static inline void wbt_requeue(struct rq_wb *rwb, struct blk_issue_stat *stat)
    +{
    +}
    +static inline void wbt_issue(struct rq_wb *rwb, struct blk_issue_stat *stat)
    +{
    +}
    +static inline void wbt_disable(struct rq_wb *rwb)
    +{
    +}
    +static inline void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth)
    +{
    +}
    +static inline void wbt_set_write_cache(struct rq_wb *rwb, bool wc)
    +{
    +}
    +
    +#endif /* CONFIG_BLK_WBT */
    +
    +#endif
    diff --git a/include/trace/events/wbt.h b/include/trace/events/wbt.h
    new file mode 100644
    index 000000000000..3c518e455680
    --- /dev/null
    +++ b/include/trace/events/wbt.h
    @@ -0,0 +1,153 @@
    +#undef TRACE_SYSTEM
    +#define TRACE_SYSTEM wbt
    +
    +#if !defined(_TRACE_WBT_H) || defined(TRACE_HEADER_MULTI_READ)
    +#define _TRACE_WBT_H
    +
    +#include <linux/tracepoint.h>
    +#include "../../../block/blk-wbt.h"
    +
    +/**
    + * wbt_stat - trace stats for blk_wb
    + * @stat: array of read/write stats
    + */
    +TRACE_EVENT(wbt_stat,
    +
    + TP_PROTO(struct backing_dev_info *bdi, struct blk_rq_stat *stat),
    +
    + TP_ARGS(bdi, stat),
    +
    + TP_STRUCT__entry(
    + __array(char, name, 32)
    + __field(s64, rmean)
    + __field(u64, rmin)
    + __field(u64, rmax)
    + __field(s64, rnr_samples)
    + __field(s64, rtime)
    + __field(s64, wmean)
    + __field(u64, wmin)
    + __field(u64, wmax)
    + __field(s64, wnr_samples)
    + __field(s64, wtime)
    + ),
    +
    + TP_fast_assign(
    + strncpy(__entry->name, dev_name(bdi->dev), 32);
    + __entry->rmean = stat[0].mean;
    + __entry->rmin = stat[0].min;
    + __entry->rmax = stat[0].max;
    + __entry->rnr_samples = stat[0].nr_samples;
    + __entry->wmean = stat[1].mean;
    + __entry->wmin = stat[1].min;
    + __entry->wmax = stat[1].max;
    + __entry->wnr_samples = stat[1].nr_samples;
    + ),
    +
    + TP_printk("%s: rmean=%llu, rmin=%llu, rmax=%llu, rsamples=%llu, "
    + "wmean=%llu, wmin=%llu, wmax=%llu, wsamples=%llu\n",
    + __entry->name, __entry->rmean, __entry->rmin, __entry->rmax,
    + __entry->rnr_samples, __entry->wmean, __entry->wmin,
    + __entry->wmax, __entry->wnr_samples)
    +);
    +
    +/**
    + * wbt_lat - trace latency event
    + * @lat: latency trigger
    + */
    +TRACE_EVENT(wbt_lat,
    +
    + TP_PROTO(struct backing_dev_info *bdi, unsigned long lat),
    +
    + TP_ARGS(bdi, lat),
    +
    + TP_STRUCT__entry(
    + __array(char, name, 32)
    + __field(unsigned long, lat)
    + ),
    +
    + TP_fast_assign(
    + strncpy(__entry->name, dev_name(bdi->dev), 32);
    + __entry->lat = div_u64(lat, 1000);
    + ),
    +
    + TP_printk("%s: latency %lluus\n", __entry->name,
    + (unsigned long long) __entry->lat)
    +);
    +
    +/**
    + * wbt_step - trace wb event step
    + * @msg: context message
    + * @step: the current scale step count
    + * @window: the current monitoring window
    + * @bg: the current background queue limit
    + * @normal: the current normal writeback limit
    + * @max: the current max throughput writeback limit
    + */
    +TRACE_EVENT(wbt_step,
    +
    + TP_PROTO(struct backing_dev_info *bdi, const char *msg,
    + int step, unsigned long window, unsigned int bg,
    + unsigned int normal, unsigned int max),
    +
    + TP_ARGS(bdi, msg, step, window, bg, normal, max),
    +
    + TP_STRUCT__entry(
    + __array(char, name, 32)
    + __field(const char *, msg)
    + __field(int, step)
    + __field(unsigned long, window)
    + __field(unsigned int, bg)
    + __field(unsigned int, normal)
    + __field(unsigned int, max)
    + ),
    +
    + TP_fast_assign(
    + strncpy(__entry->name, dev_name(bdi->dev), 32);
    + __entry->msg = msg;
    + __entry->step = step;
    + __entry->window = div_u64(window, 1000);
    + __entry->bg = bg;
    + __entry->normal = normal;
    + __entry->max = max;
    + ),
    +
    + TP_printk("%s: %s: step=%d, window=%luus, background=%u, normal=%u, max=%u\n",
    + __entry->name, __entry->msg, __entry->step, __entry->window,
    + __entry->bg, __entry->normal, __entry->max)
    +);
    +
    +/**
    + * wbt_timer - trace wb timer event
    + * @status: timer state status
    + * @step: the current scale step count
    + * @inflight: tracked writes inflight
    + */
    +TRACE_EVENT(wbt_timer,
    +
    + TP_PROTO(struct backing_dev_info *bdi, unsigned int status,
    + int step, unsigned int inflight),
    +
    + TP_ARGS(bdi, status, step, inflight),
    +
    + TP_STRUCT__entry(
    + __array(char, name, 32)
    + __field(unsigned int, status)
    + __field(int, step)
    + __field(unsigned int, inflight)
    + ),
    +
    + TP_fast_assign(
    + strncpy(__entry->name, dev_name(bdi->dev), 32);
    + __entry->status = status;
    + __entry->step = step;
    + __entry->inflight = inflight;
    + ),
    +
    + TP_printk("%s: status=%u, step=%d, inflight=%u\n", __entry->name,
    + __entry->status, __entry->step, __entry->inflight)
    +);
    +
    +#endif /* _TRACE_WBT_H */
    +
    +/* This part must be outside protection */
    +#include <trace/define_trace.h>
    --
    2.7.4
    \
     
     \ /
      Last update: 2016-11-01 22:12    [W:4.012 / U:0.312 seconds]
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