blk-rq-qos.c

// 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;

	has_sleeper = !prepare_to_wait_exclusive(&rqw->wait, &data.wq,
						 TASK_UNINTERRUPTIBLE);
	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)
{
	while (q->rq_qos) {
		struct rq_qos *rqos = q->rq_qos;
		q->rq_qos = rqos->next;
		rqos->ops->exit(rqos);
	}
}