linux/block/blk-rq-qos.c
Harshad Shirwadkar b84477d3eb blk-wbt: fix performance regression in wbt scale_up/scale_down
scale_up wakes up waiters after scaling up. But after scaling max, it
should not wake up more waiters as waiters will not have anything to
do. This patch fixes this by making scale_up (and also scale_down)
return when threshold is reached.

This bug causes increased fdatasync latency when fdatasync and dd
conv=sync are performed in parallel on 4.19 compared to 4.14. This
bug was introduced during refactoring of blk-wbt code.

Fixes: a79050434b ("blk-rq-qos: refactor out common elements of blk-wbt")
Cc: stable@vger.kernel.org
Cc: Josef Bacik <jbacik@fb.com>
Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-10-06 09:26:41 -06:00

305 lines
7.1 KiB
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;
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);
}
}