Commit 64f1c21e authored by Jens Axboe's avatar Jens Axboe

blk-mq: make the polling code adaptive

The previous commit introduced the hybrid sleep/poll mode. Take
that one step further, and use the completion latencies to
automatically sleep for half the mean completion time. This is
a good approximation.

This changes the 'io_poll_delay' sysfs file a bit to expose the
various options. Depending on the value, the polling code will
behave differently:

-1	Never enter hybrid sleep mode
 0	Use half of the completion mean for the sleep delay
>0	Use this specific value as the sleep delay
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
Tested-By: default avatarStephen Bates <sbates@raithlin.com>
Reviewed-By: default avatarStephen Bates <sbates@raithlin.com>
parent 06426adf
......@@ -2132,6 +2132,11 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
*/
q->nr_requests = set->queue_depth;
/*
* Default to classic polling
*/
q->poll_nsec = -1;
if (set->ops->complete)
blk_queue_softirq_done(q, set->ops->complete);
......@@ -2469,14 +2474,70 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
}
EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);
static unsigned long blk_mq_poll_nsecs(struct request_queue *q,
struct blk_mq_hw_ctx *hctx,
struct request *rq)
{
struct blk_rq_stat stat[2];
unsigned long ret = 0;
/*
* If stats collection isn't on, don't sleep but turn it on for
* future users
*/
if (!blk_stat_enable(q))
return 0;
/*
* We don't have to do this once per IO, should optimize this
* to just use the current window of stats until it changes
*/
memset(&stat, 0, sizeof(stat));
blk_hctx_stat_get(hctx, stat);
/*
* As an optimistic guess, use half of the mean service time
* for this type of request. We can (and should) make this smarter.
* For instance, if the completion latencies are tight, we can
* get closer than just half the mean. This is especially
* important on devices where the completion latencies are longer
* than ~10 usec.
*/
if (req_op(rq) == REQ_OP_READ && stat[BLK_STAT_READ].nr_samples)
ret = (stat[BLK_STAT_READ].mean + 1) / 2;
else if (req_op(rq) == REQ_OP_WRITE && stat[BLK_STAT_WRITE].nr_samples)
ret = (stat[BLK_STAT_WRITE].mean + 1) / 2;
return ret;
}
static bool blk_mq_poll_hybrid_sleep(struct request_queue *q,
struct blk_mq_hw_ctx *hctx,
struct request *rq)
{
struct hrtimer_sleeper hs;
enum hrtimer_mode mode;
unsigned int nsecs;
ktime_t kt;
if (!q->poll_nsec || test_bit(REQ_ATOM_POLL_SLEPT, &rq->atomic_flags))
if (test_bit(REQ_ATOM_POLL_SLEPT, &rq->atomic_flags))
return false;
/*
* poll_nsec can be:
*
* -1: don't ever hybrid sleep
* 0: use half of prev avg
* >0: use this specific value
*/
if (q->poll_nsec == -1)
return false;
else if (q->poll_nsec > 0)
nsecs = q->poll_nsec;
else
nsecs = blk_mq_poll_nsecs(q, hctx, rq);
if (!nsecs)
return false;
set_bit(REQ_ATOM_POLL_SLEPT, &rq->atomic_flags);
......@@ -2485,7 +2546,7 @@ static bool blk_mq_poll_hybrid_sleep(struct request_queue *q,
* This will be replaced with the stats tracking code, using
* 'avg_completion_time / 2' as the pre-sleep target.
*/
kt = ktime_set(0, q->poll_nsec);
kt = ktime_set(0, nsecs);
mode = HRTIMER_MODE_REL;
hrtimer_init_on_stack(&hs.timer, CLOCK_MONOTONIC, mode);
......@@ -2520,7 +2581,7 @@ static bool __blk_mq_poll(struct blk_mq_hw_ctx *hctx, struct request *rq)
* the IO isn't complete, we'll get called again and will go
* straight to the busy poll loop.
*/
if (blk_mq_poll_hybrid_sleep(q, rq))
if (blk_mq_poll_hybrid_sleep(q, hctx, rq))
return true;
hctx->poll_considered++;
......
......@@ -352,24 +352,34 @@ queue_rq_affinity_store(struct request_queue *q, const char *page, size_t count)
static ssize_t queue_poll_delay_show(struct request_queue *q, char *page)
{
return queue_var_show(q->poll_nsec / 1000, page);
int val;
if (q->poll_nsec == -1)
val = -1;
else
val = q->poll_nsec / 1000;
return sprintf(page, "%d\n", val);
}
static ssize_t queue_poll_delay_store(struct request_queue *q, const char *page,
size_t count)
{
unsigned long poll_usec;
ssize_t ret;
int err, val;
if (!q->mq_ops || !q->mq_ops->poll)
return -EINVAL;
ret = queue_var_store(&poll_usec, page, count);
if (ret < 0)
return ret;
err = kstrtoint(page, 10, &val);
if (err < 0)
return err;
q->poll_nsec = poll_usec * 1000;
return ret;
if (val == -1)
q->poll_nsec = -1;
else
q->poll_nsec = val * 1000;
return count;
}
static ssize_t queue_poll_show(struct request_queue *q, char *page)
......
......@@ -509,7 +509,7 @@ struct request_queue {
unsigned int request_fn_active;
unsigned int rq_timeout;
unsigned int poll_nsec;
int poll_nsec;
struct timer_list timeout;
struct work_struct timeout_work;
struct list_head timeout_list;
......
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