// SPDX-License-Identifier: GPL-2.0

  /*
   * 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"

  #include "blk-rq-qos.h"

  
  #define CREATE_TRACE_POINTS
  #include <trace/events/wbt.h>

  static inline void wbt_clear_state(struct request *rq)

  {

  	rq->wbt_flags = 0;

  }

  static inline enum wbt_flags wbt_flags(struct request *rq)

  {

  	return rq->wbt_flags;

  }

  static inline bool wbt_is_tracked(struct request *rq)

  {

  	return rq->wbt_flags & WBT_TRACKED;

  }

  static inline bool wbt_is_read(struct request *rq)

  {

  	return rq->wbt_flags & WBT_READ;

  }

  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;
  }

  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->rqos.q->backing_dev_info->wb;

  
  	return time_before(jiffies, wb->dirty_sleep + HZ);
  }

  static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb,
  					  enum wbt_flags wb_acct)

  {

  	if (wb_acct & WBT_KSWAPD)
  		return &rwb->rq_wait[WBT_RWQ_KSWAPD];

  	else if (wb_acct & WBT_DISCARD)
  		return &rwb->rq_wait[WBT_RWQ_DISCARD];

  
  	return &rwb->rq_wait[WBT_RWQ_BG];

  }
  
  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 (wq_has_sleeper(&rqw->wait))

  			wake_up_all(&rqw->wait);
  	}
  }

  static void wbt_rqw_done(struct rq_wb *rwb, struct rq_wait *rqw,
  			 enum wbt_flags wb_acct)

  {

  	int inflight, limit;

  	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;
  	}
  
  	/*

  	 * For discards, our limit is always the background. For writes, if
  	 * the device does write back caching, drop further down before we
  	 * wake people up.

  	 */

  	if (wb_acct & WBT_DISCARD)
  		limit = rwb->wb_background;
  	else 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 (wq_has_sleeper(&rqw->wait)) {

  		int diff = limit - inflight;
  
  		if (!inflight || diff >= rwb->wb_background / 2)

  			wake_up_all(&rqw->wait);

  	}
  }

  static void __wbt_done(struct rq_qos *rqos, enum wbt_flags wb_acct)
  {
  	struct rq_wb *rwb = RQWB(rqos);
  	struct rq_wait *rqw;
  
  	if (!(wb_acct & WBT_TRACKED))
  		return;
  
  	rqw = get_rq_wait(rwb, wb_acct);
  	wbt_rqw_done(rwb, rqw, wb_acct);
  }

  /*
   * Called on completion of a request. Note that it's also called when
   * a request is merged, when the request gets freed.
   */

  static void wbt_done(struct rq_qos *rqos, struct request *rq)

  {

  	struct rq_wb *rwb = RQWB(rqos);

  	if (!wbt_is_tracked(rq)) {
  		if (rwb->sync_cookie == rq) {

  			rwb->sync_issue = 0;
  			rwb->sync_cookie = NULL;
  		}

  		if (wbt_is_read(rq))

  			wb_timestamp(rwb, &rwb->last_comp);

  	} else {

  		WARN_ON_ONCE(rq == rwb->sync_cookie);

  		__wbt_done(rqos, wbt_flags(rq));

  	}

  	wbt_clear_state(rq);

  }

  static inline bool 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[READ].nr_samples >= 1 &&
  		stat[WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES);

  }
  
  static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
  {

  	u64 now, issue = READ_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)

  {

  	struct backing_dev_info *bdi = rwb->rqos.q->backing_dev_info;
  	struct rq_depth *rqd = &rwb->rq_depth;

  	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[READ].nr_samples)) {

  		trace_wbt_lat(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[WRITE].nr_samples || 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[READ].min > rwb->min_lat_nsec) {
  		trace_wbt_lat(bdi, stat[READ].min);

  		trace_wbt_stat(bdi, stat);

  		return LAT_EXCEEDED;
  	}

  	if (rqd->scale_step)

  		trace_wbt_stat(bdi, stat);

  
  	return LAT_OK;
  }

  static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
  {

  	struct backing_dev_info *bdi = rwb->rqos.q->backing_dev_info;
  	struct rq_depth *rqd = &rwb->rq_depth;

  	trace_wbt_step(bdi, msg, rqd->scale_step, rwb->cur_win_nsec,
  			rwb->wb_background, rwb->wb_normal, rqd->max_depth);

  }

  static void calc_wb_limits(struct rq_wb *rwb)

  {

  	if (rwb->min_lat_nsec == 0) {
  		rwb->wb_normal = rwb->wb_background = 0;
  	} else if (rwb->rq_depth.max_depth <= 2) {
  		rwb->wb_normal = rwb->rq_depth.max_depth;
  		rwb->wb_background = 1;
  	} else {
  		rwb->wb_normal = (rwb->rq_depth.max_depth + 1) / 2;
  		rwb->wb_background = (rwb->rq_depth.max_depth + 3) / 4;
  	}
  }

  static void scale_up(struct rq_wb *rwb)
  {

  	if (!rq_depth_scale_up(&rwb->rq_depth))
  		return;

  	calc_wb_limits(rwb);

  	rwb->unknown_cnt = 0;

  	rwb_wake_all(rwb);

  	rwb_trace_step(rwb, tracepoint_string("scale up"));

  }

  static void scale_down(struct rq_wb *rwb, bool hard_throttle)
  {

  	if (!rq_depth_scale_down(&rwb->rq_depth, hard_throttle))
  		return;

  	calc_wb_limits(rwb);

  	rwb->unknown_cnt = 0;

  	rwb_trace_step(rwb, tracepoint_string("scale down"));

  }
  
  static void rwb_arm_timer(struct rq_wb *rwb)
  {

  	struct rq_depth *rqd = &rwb->rq_depth;
  
  	if (rqd->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((rqd->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;
  	}

  	blk_stat_activate_nsecs(rwb->cb, rwb->cur_win_nsec);

  }

  static void wb_timer_fn(struct blk_stat_callback *cb)

  {

  	struct rq_wb *rwb = cb->data;

  	struct rq_depth *rqd = &rwb->rq_depth;

  	unsigned int inflight = wbt_inflight(rwb);
  	int status;

  	status = latency_exceeded(rwb, cb->stat);

  	trace_wbt_timer(rwb->rqos.q->backing_dev_info, status, rqd->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 (rqd->scale_step > 0)

  			scale_up(rwb);

  		else if (rqd->scale_step < 0)

  			scale_down(rwb, false);
  		break;
  	default:
  		break;
  	}
  
  	/*
  	 * Re-arm timer, if we have IO in flight
  	 */

  	if (rqd->scale_step || inflight)

  		rwb_arm_timer(rwb);
  }

  static void wbt_update_limits(struct rq_wb *rwb)

  {

  	struct rq_depth *rqd = &rwb->rq_depth;
  
  	rqd->scale_step = 0;
  	rqd->scaled_max = false;
  
  	rq_depth_calc_max_depth(rqd);

  	calc_wb_limits(rwb);
  
  	rwb_wake_all(rwb);
  }

  u64 wbt_get_min_lat(struct request_queue *q)
  {
  	struct rq_qos *rqos = wbt_rq_qos(q);
  	if (!rqos)
  		return 0;
  	return RQWB(rqos)->min_lat_nsec;
  }
  
  void wbt_set_min_lat(struct request_queue *q, u64 val)
  {
  	struct rq_qos *rqos = wbt_rq_qos(q);
  	if (!rqos)
  		return;
  	RQWB(rqos)->min_lat_nsec = val;
  	RQWB(rqos)->enable_state = WBT_STATE_ON_MANUAL;

  	wbt_update_limits(RQWB(rqos));

  }

  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;

  	/*
  	 * If we got disabled, just return UINT_MAX. This ensures that
  	 * we'll properly inc a new IO, and dec+wakeup at the end.
  	 */
  	if (!rwb_enabled(rwb))
  		return UINT_MAX;

  	if ((rw & REQ_OP_MASK) == REQ_OP_DISCARD)
  		return rwb->wb_background;

  	/*
  	 * At this point we know it's a buffered write. If this is

  	 * kswapd trying to free memory, or REQ_SYNC is 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->rq_depth.max_depth;

  	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;
  }

  struct wbt_wait_data {

  	struct rq_wb *rwb;

  	enum wbt_flags wb_acct;

  	unsigned long rw;

  };

  static bool wbt_inflight_cb(struct rq_wait *rqw, void *private_data)

  {

  	struct wbt_wait_data *data = private_data;
  	return rq_wait_inc_below(rqw, get_limit(data->rwb, data->rw));
  }

  static void wbt_cleanup_cb(struct rq_wait *rqw, void *private_data)
  {
  	struct wbt_wait_data *data = private_data;
  	wbt_rqw_done(data->rwb, rqw, data->wb_acct);

  }

  /*
   * 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, enum wbt_flags wb_acct,

  		       unsigned long rw)

  {

  	struct rq_wait *rqw = get_rq_wait(rwb, wb_acct);

  	struct wbt_wait_data data = {

  		.rwb = rwb,

  		.wb_acct = wb_acct,

  		.rw = rw,
  	};

  	rq_qos_wait(rqw, &data, wbt_inflight_cb, wbt_cleanup_cb);

  }
  
  static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio)
  {

  	switch (bio_op(bio)) {
  	case REQ_OP_WRITE:
  		/*
  		 * Don't throttle WRITE_ODIRECT
  		 */
  		if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) ==
  		    (REQ_SYNC | REQ_IDLE))
  			return false;

  		fallthrough;

  	case REQ_OP_DISCARD:
  		return true;
  	default:

  		return false;

  	}

  }

  static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, struct bio *bio)
  {
  	enum wbt_flags flags = 0;

  	if (!rwb_enabled(rwb))
  		return 0;

  	if (bio_op(bio) == REQ_OP_READ) {
  		flags = WBT_READ;
  	} else if (wbt_should_throttle(rwb, bio)) {
  		if (current_is_kswapd())
  			flags |= WBT_KSWAPD;
  		if (bio_op(bio) == REQ_OP_DISCARD)
  			flags |= WBT_DISCARD;
  		flags |= WBT_TRACKED;
  	}
  	return flags;
  }
  
  static void wbt_cleanup(struct rq_qos *rqos, struct bio *bio)
  {
  	struct rq_wb *rwb = RQWB(rqos);
  	enum wbt_flags flags = bio_to_wbt_flags(rwb, bio);
  	__wbt_done(rqos, flags);
  }

  /*
   * 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.
   */

  static void wbt_wait(struct rq_qos *rqos, struct bio *bio)

  {

  	struct rq_wb *rwb = RQWB(rqos);

  	enum wbt_flags flags;

  	flags = bio_to_wbt_flags(rwb, bio);

  	if (!(flags & WBT_TRACKED)) {

  		if (flags & WBT_READ)

  			wb_timestamp(rwb, &rwb->last_issue);

  		return;

  	}

  	__wbt_wait(rwb, flags, bio->bi_opf);

  	if (!blk_stat_is_active(rwb->cb))

  		rwb_arm_timer(rwb);

  }

  static void wbt_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
  {
  	struct rq_wb *rwb = RQWB(rqos);
  	rq->wbt_flags |= bio_to_wbt_flags(rwb, bio);

  }

  static void wbt_issue(struct rq_qos *rqos, struct request *rq)

  {

  	struct rq_wb *rwb = RQWB(rqos);

  	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. The request can go away when it 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(rq) && !rwb->sync_issue) {
  		rwb->sync_cookie = rq;

  		rwb->sync_issue = rq->io_start_time_ns;

  	}
  }

  static void wbt_requeue(struct rq_qos *rqos, struct request *rq)

  {

  	struct rq_wb *rwb = RQWB(rqos);

  	if (!rwb_enabled(rwb))
  		return;

  	if (rq == rwb->sync_cookie) {

  		rwb->sync_issue = 0;
  		rwb->sync_cookie = NULL;
  	}
  }

  void wbt_set_write_cache(struct request_queue *q, bool write_cache_on)

  {

  	struct rq_qos *rqos = wbt_rq_qos(q);
  	if (rqos)
  		RQWB(rqos)->wc = write_cache_on;

  }

  /*
   * Enable wbt if defaults are configured that way
   */
  void wbt_enable_default(struct request_queue *q)
  {

  	struct rq_qos *rqos = wbt_rq_qos(q);

  	/* Throttling already enabled? */

  	if (rqos)

  		return;
  
  	/* Queue not registered? Maybe shutting down... */

  	if (!blk_queue_registered(q))

  		return;

  	if (queue_is_mq(q) && IS_ENABLED(CONFIG_BLK_WBT_MQ))

  		wbt_init(q);
  }
  EXPORT_SYMBOL_GPL(wbt_enable_default);

  u64 wbt_default_latency_nsec(struct request_queue *q)
  {
  	/*
  	 * We default to 2msec for non-rotational storage, and 75msec
  	 * for rotational storage.
  	 */
  	if (blk_queue_nonrot(q))
  		return 2000000ULL;
  	else
  		return 75000000ULL;
  }

  static int wbt_data_dir(const struct request *rq)
  {

  	const int op = req_op(rq);
  
  	if (op == REQ_OP_READ)
  		return READ;

  	else if (op_is_write(op))

  		return WRITE;
  
  	/* don't account */
  	return -1;

  }

  static void wbt_queue_depth_changed(struct rq_qos *rqos)
  {
  	RQWB(rqos)->rq_depth.queue_depth = blk_queue_depth(rqos->q);

  	wbt_update_limits(RQWB(rqos));

  }

  static void wbt_exit(struct rq_qos *rqos)
  {
  	struct rq_wb *rwb = RQWB(rqos);
  	struct request_queue *q = rqos->q;
  
  	blk_stat_remove_callback(q, rwb->cb);
  	blk_stat_free_callback(rwb->cb);
  	kfree(rwb);
  }
  
  /*
   * Disable wbt, if enabled by default.
   */
  void wbt_disable_default(struct request_queue *q)
  {
  	struct rq_qos *rqos = wbt_rq_qos(q);
  	struct rq_wb *rwb;
  	if (!rqos)
  		return;
  	rwb = RQWB(rqos);

  	if (rwb->enable_state == WBT_STATE_ON_DEFAULT) {
  		blk_stat_deactivate(rwb->cb);

  		rwb->wb_normal = 0;

  	}

  }

  EXPORT_SYMBOL_GPL(wbt_disable_default);

  #ifdef CONFIG_BLK_DEBUG_FS
  static int wbt_curr_win_nsec_show(void *data, struct seq_file *m)
  {
  	struct rq_qos *rqos = data;
  	struct rq_wb *rwb = RQWB(rqos);
  
  	seq_printf(m, "%llu
  ", rwb->cur_win_nsec);
  	return 0;
  }
  
  static int wbt_enabled_show(void *data, struct seq_file *m)
  {
  	struct rq_qos *rqos = data;
  	struct rq_wb *rwb = RQWB(rqos);
  
  	seq_printf(m, "%d
  ", rwb->enable_state);
  	return 0;
  }
  
  static int wbt_id_show(void *data, struct seq_file *m)
  {
  	struct rq_qos *rqos = data;
  
  	seq_printf(m, "%u
  ", rqos->id);
  	return 0;
  }
  
  static int wbt_inflight_show(void *data, struct seq_file *m)
  {
  	struct rq_qos *rqos = data;
  	struct rq_wb *rwb = RQWB(rqos);
  	int i;
  
  	for (i = 0; i < WBT_NUM_RWQ; i++)
  		seq_printf(m, "%d: inflight %d
  ", i,
  			   atomic_read(&rwb->rq_wait[i].inflight));
  	return 0;
  }
  
  static int wbt_min_lat_nsec_show(void *data, struct seq_file *m)
  {
  	struct rq_qos *rqos = data;
  	struct rq_wb *rwb = RQWB(rqos);
  
  	seq_printf(m, "%lu
  ", rwb->min_lat_nsec);
  	return 0;
  }
  
  static int wbt_unknown_cnt_show(void *data, struct seq_file *m)
  {
  	struct rq_qos *rqos = data;
  	struct rq_wb *rwb = RQWB(rqos);
  
  	seq_printf(m, "%u
  ", rwb->unknown_cnt);
  	return 0;
  }
  
  static int wbt_normal_show(void *data, struct seq_file *m)
  {
  	struct rq_qos *rqos = data;
  	struct rq_wb *rwb = RQWB(rqos);
  
  	seq_printf(m, "%u
  ", rwb->wb_normal);
  	return 0;
  }
  
  static int wbt_background_show(void *data, struct seq_file *m)
  {
  	struct rq_qos *rqos = data;
  	struct rq_wb *rwb = RQWB(rqos);
  
  	seq_printf(m, "%u
  ", rwb->wb_background);
  	return 0;
  }
  
  static const struct blk_mq_debugfs_attr wbt_debugfs_attrs[] = {
  	{"curr_win_nsec", 0400, wbt_curr_win_nsec_show},
  	{"enabled", 0400, wbt_enabled_show},
  	{"id", 0400, wbt_id_show},
  	{"inflight", 0400, wbt_inflight_show},
  	{"min_lat_nsec", 0400, wbt_min_lat_nsec_show},
  	{"unknown_cnt", 0400, wbt_unknown_cnt_show},
  	{"wb_normal", 0400, wbt_normal_show},
  	{"wb_background", 0400, wbt_background_show},
  	{},
  };
  #endif

  static struct rq_qos_ops wbt_rqos_ops = {
  	.throttle = wbt_wait,
  	.issue = wbt_issue,

  	.track = wbt_track,

  	.requeue = wbt_requeue,
  	.done = wbt_done,

  	.cleanup = wbt_cleanup,

  	.queue_depth_changed = wbt_queue_depth_changed,

  	.exit = wbt_exit,

  #ifdef CONFIG_BLK_DEBUG_FS
  	.debugfs_attrs = wbt_debugfs_attrs,
  #endif

  };

  int wbt_init(struct request_queue *q)

  {
  	struct rq_wb *rwb;
  	int i;

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

  	rwb->cb = blk_stat_alloc_callback(wb_timer_fn, wbt_data_dir, 2, rwb);

  	if (!rwb->cb) {
  		kfree(rwb);
  		return -ENOMEM;
  	}

  	for (i = 0; i < WBT_NUM_RWQ; i++)
  		rq_wait_init(&rwb->rq_wait[i]);

  	rwb->rqos.id = RQ_QOS_WBT;
  	rwb->rqos.ops = &wbt_rqos_ops;
  	rwb->rqos.q = q;

  	rwb->last_comp = rwb->last_issue = jiffies;

  	rwb->win_nsec = RWB_WINDOW_NSEC;

  	rwb->enable_state = WBT_STATE_ON_DEFAULT;

  	rwb->wc = 1;
  	rwb->rq_depth.default_depth = RWB_DEF_DEPTH;

  	wbt_update_limits(rwb);

  
  	/*

  	 * Assign rwb and add the stats callback.

  	 */

  	rq_qos_add(q, &rwb->rqos);

  	blk_stat_add_callback(q, rwb->cb);

  	rwb->min_lat_nsec = wbt_default_latency_nsec(q);

  	wbt_queue_depth_changed(&rwb->rqos);

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

  
  	return 0;
  }