blk-wbt: add general throttling mechanism (e34cbd30) · Commits · e / devices / android_kernel_fairphone_FP5

block/Makefile

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		@@ -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

block/blk-wbt.c

0 → 100644

+735 −0

Original line number	Diff line number	Diff line
		/*
		* 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_all(&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:
		/*
		* 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.
		*/
		scale_up(rwb);
		break;
		case LAT_UNKNOWN:
		if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
		break;
		/*
		* We get here when 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).
		*/
		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,
		wait_queue_t *wait, 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;
		}

		/*
		* If the waitqueue is already active and we are not the next
		* in line to be woken up, wait for our turn.
		*/
		if (waitqueue_active(&rqw->wait) &&
		rqw->wait.task_list.next != &wait->task_list)
		return false;

		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, &wait, rw))
		return;

		do {
		prepare_to_wait_exclusive(&rqw->wait, &wait,
		TASK_UNINTERRUPTIBLE);

		if (may_queue(rwb, rqw, &wait, 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);

		int wbt_init(struct request_queue q, struct wb_stat_ops ops)
		{
		struct rq_wb *rwb;
		int i;

		/*
		* For now, we depend on the stats window being larger than
		* our monitoring window. Ensure that this isn't inadvertently
		* violated.
		*/
		BUILD_BUG_ON(RWB_WINDOW_NSEC > BLK_STAT_NSEC);
		BUILD_BUG_ON(WBT_NR_BITS > BLK_STAT_RES_BITS);

		if (!ops->get \|\| !ops->is_current \|\| !ops->clear)
		return -EINVAL;

		rwb = kzalloc(sizeof(*rwb), GFP_KERNEL);
		if (!rwb)
		return -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 = &q->backing_dev_info;
		rwb->win_nsec = RWB_WINDOW_NSEC;
		rwb->stat_ops = ops;
		rwb->ops_data = q;
		wbt_update_limits(rwb);

		/*
		* Assign rwb, and turn on stats tracking for this queue
		*/
		q->rq_wb = rwb;
		blk_stat_enable(q);

		if (blk_queue_nonrot(q))
		rwb->min_lat_nsec = 2000000ULL;
		else
		rwb->min_lat_nsec = 75000000ULL;

		wbt_set_queue_depth(rwb, blk_queue_depth(q));
		wbt_set_write_cache(rwb, test_bit(QUEUE_FLAG_WC, &q->queue_flags));

		return 0;
		}

		void wbt_exit(struct request_queue *q)
		{
		struct rq_wb *rwb = q->rq_wb;

		if (rwb) {
		del_timer_sync(&rwb->window_timer);
		q->rq_wb = NULL;
		kfree(rwb);
		}
		}

block/blk-wbt.h

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Original line number	Diff line number	Diff line
		#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 *);
		int wbt_init(struct request_queue , struct wb_stat_ops );
		void wbt_exit(struct request_queue *);
		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 int wbt_init(struct request_queue q, struct wb_stat_ops ops)
		{
		return -EINVAL;
		}
		static inline void wbt_exit(struct request_queue *q)
		{
		}
		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

include/trace/events/wbt.h

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