// SPDX-License-Identifier: GPL-2.0

  #include "blk-rq-qos.h"

  /*
   * 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, unsigned int below)

  {

  	unsigned int cur = atomic_read(v);

  
  	for (;;) {

  		unsigned int old;

  
  		if (cur >= below)
  			return false;
  		old = atomic_cmpxchg(v, cur, cur + 1);
  		if (old == cur)
  			break;
  		cur = old;
  	}
  
  	return true;
  }

  bool rq_wait_inc_below(struct rq_wait *rq_wait, unsigned int limit)

  {
  	return atomic_inc_below(&rq_wait->inflight, limit);
  }

  void __rq_qos_cleanup(struct rq_qos *rqos, struct bio *bio)

  {

  	do {

  		if (rqos->ops->cleanup)

  			rqos->ops->cleanup(rqos, bio);

  		rqos = rqos->next;
  	} while (rqos);

  }

  void __rq_qos_done(struct rq_qos *rqos, struct request *rq)

  {

  	do {

  		if (rqos->ops->done)
  			rqos->ops->done(rqos, rq);

  		rqos = rqos->next;
  	} while (rqos);

  }

  void __rq_qos_issue(struct rq_qos *rqos, struct request *rq)

  {

  	do {

  		if (rqos->ops->issue)
  			rqos->ops->issue(rqos, rq);

  		rqos = rqos->next;
  	} while (rqos);

  }

  void __rq_qos_requeue(struct rq_qos *rqos, struct request *rq)

  {

  	do {

  		if (rqos->ops->requeue)
  			rqos->ops->requeue(rqos, rq);

  		rqos = rqos->next;
  	} while (rqos);

  }

  void __rq_qos_throttle(struct rq_qos *rqos, struct bio *bio)

  {

  	do {

  		if (rqos->ops->throttle)

  			rqos->ops->throttle(rqos, bio);

  		rqos = rqos->next;
  	} while (rqos);

  }

  void __rq_qos_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)

  {

  	do {

  		if (rqos->ops->track)
  			rqos->ops->track(rqos, rq, bio);

  		rqos = rqos->next;
  	} while (rqos);
  }
  
  void __rq_qos_merge(struct rq_qos *rqos, struct request *rq, struct bio *bio)
  {
  	do {
  		if (rqos->ops->merge)
  			rqos->ops->merge(rqos, rq, bio);

  		rqos = rqos->next;
  	} while (rqos);

  }

  void __rq_qos_done_bio(struct rq_qos *rqos, struct bio *bio)

  {

  	do {

  		if (rqos->ops->done_bio)
  			rqos->ops->done_bio(rqos, bio);

  		rqos = rqos->next;
  	} while (rqos);

  }

  void __rq_qos_queue_depth_changed(struct rq_qos *rqos)
  {
  	do {
  		if (rqos->ops->queue_depth_changed)
  			rqos->ops->queue_depth_changed(rqos);
  		rqos = rqos->next;
  	} while (rqos);
  }

  /*
   * Return true, if we can't increase the depth further by scaling
   */
  bool rq_depth_calc_max_depth(struct rq_depth *rqd)
  {
  	unsigned int depth;
  	bool ret = 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 (rqd->queue_depth == 1) {
  		if (rqd->scale_step > 0)
  			rqd->max_depth = 1;
  		else {
  			rqd->max_depth = 2;
  			ret = true;
  		}
  	} 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, rqd->default_depth,
  			      rqd->queue_depth);
  		if (rqd->scale_step > 0)
  			depth = 1 + ((depth - 1) >> min(31, rqd->scale_step));
  		else if (rqd->scale_step < 0) {
  			unsigned int maxd = 3 * rqd->queue_depth / 4;
  
  			depth = 1 + ((depth - 1) << -rqd->scale_step);
  			if (depth > maxd) {
  				depth = maxd;
  				ret = true;
  			}
  		}
  
  		rqd->max_depth = depth;
  	}
  
  	return ret;
  }

  /* Returns true on success and false if scaling up wasn't possible */
  bool rq_depth_scale_up(struct rq_depth *rqd)

  {
  	/*
  	 * Hit max in previous round, stop here
  	 */
  	if (rqd->scaled_max)

  		return false;

  
  	rqd->scale_step--;
  
  	rqd->scaled_max = rq_depth_calc_max_depth(rqd);

  	return true;

  }
  
  /*
   * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we

   * had a latency violation. Returns true on success and returns false if
   * scaling down wasn't possible.

   */

  bool rq_depth_scale_down(struct rq_depth *rqd, 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 (rqd->max_depth == 1)

  		return false;

  
  	if (rqd->scale_step < 0 && hard_throttle)
  		rqd->scale_step = 0;
  	else
  		rqd->scale_step++;
  
  	rqd->scaled_max = false;
  	rq_depth_calc_max_depth(rqd);

  	return true;

  }

  struct rq_qos_wait_data {
  	struct wait_queue_entry wq;
  	struct task_struct *task;
  	struct rq_wait *rqw;
  	acquire_inflight_cb_t *cb;
  	void *private_data;
  	bool got_token;
  };
  
  static int rq_qos_wake_function(struct wait_queue_entry *curr,
  				unsigned int mode, int wake_flags, void *key)
  {
  	struct rq_qos_wait_data *data = container_of(curr,
  						     struct rq_qos_wait_data,
  						     wq);
  
  	/*
  	 * If we fail to get a budget, return -1 to interrupt the wake up loop
  	 * in __wake_up_common.
  	 */
  	if (!data->cb(data->rqw, data->private_data))
  		return -1;
  
  	data->got_token = true;

  	smp_wmb();

  	list_del_init(&curr->entry);
  	wake_up_process(data->task);
  	return 1;
  }
  
  /**
   * rq_qos_wait - throttle on a rqw if we need to

   * @rqw: rqw to throttle on
   * @private_data: caller provided specific data
   * @acquire_inflight_cb: inc the rqw->inflight counter if we can
   * @cleanup_cb: the callback to cleanup in case we race with a waker

   *
   * This provides a uniform place for the rq_qos users to do their throttling.
   * Since you can end up with a lot of things sleeping at once, this manages the
   * waking up based on the resources available.  The acquire_inflight_cb should
   * inc the rqw->inflight if we have the ability to do so, or return false if not
   * and then we will sleep until the room becomes available.
   *
   * cleanup_cb is in case that we race with a waker and need to cleanup the
   * inflight count accordingly.
   */
  void rq_qos_wait(struct rq_wait *rqw, void *private_data,
  		 acquire_inflight_cb_t *acquire_inflight_cb,
  		 cleanup_cb_t *cleanup_cb)
  {
  	struct rq_qos_wait_data data = {
  		.wq = {
  			.func	= rq_qos_wake_function,
  			.entry	= LIST_HEAD_INIT(data.wq.entry),
  		},
  		.task = current,
  		.rqw = rqw,
  		.cb = acquire_inflight_cb,
  		.private_data = private_data,
  	};
  	bool has_sleeper;
  
  	has_sleeper = wq_has_sleeper(&rqw->wait);
  	if (!has_sleeper && acquire_inflight_cb(rqw, private_data))
  		return;
  
  	prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);

  	has_sleeper = !wq_has_single_sleeper(&rqw->wait);

  	do {

  		/* The memory barrier in set_task_state saves us here. */

  		if (data.got_token)
  			break;
  		if (!has_sleeper && acquire_inflight_cb(rqw, private_data)) {
  			finish_wait(&rqw->wait, &data.wq);
  
  			/*
  			 * We raced with wbt_wake_function() getting a token,
  			 * which means we now have two. Put our local token
  			 * and wake anyone else potentially waiting for one.
  			 */

  			smp_rmb();

  			if (data.got_token)
  				cleanup_cb(rqw, private_data);
  			break;
  		}
  		io_schedule();

  		has_sleeper = true;

  		set_current_state(TASK_UNINTERRUPTIBLE);

  	} while (1);
  	finish_wait(&rqw->wait, &data.wq);
  }

  void rq_qos_exit(struct request_queue *q)
  {

  	blk_mq_debugfs_unregister_queue_rqos(q);

  	while (q->rq_qos) {
  		struct rq_qos *rqos = q->rq_qos;
  		q->rq_qos = rqos->next;
  		rqos->ops->exit(rqos);
  	}
  }