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authorJens Axboe <axboe@fb.com>2016-11-14 13:03:03 -0700
committerJens Axboe <axboe@fb.com>2016-11-17 13:34:57 -0700
commit64f1c21e86f7fe63337b5c23c129de3ec506431d (patch)
treec5cfcf1875785d425b7da3f9d47388d39c9e7793 /block
parent06426adf072bca62ac31ea396ff2159a34f276c2 (diff)
downloadlinux-stericsson-64f1c21e86f7fe63337b5c23c129de3ec506431d.tar.gz
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: Jens Axboe <axboe@fb.com> Tested-By: Stephen Bates <sbates@raithlin.com> Reviewed-By: Stephen Bates <sbates@raithlin.com>
Diffstat (limited to 'block')
-rw-r--r--block/blk-mq.c67
-rw-r--r--block/blk-sysfs.c26
2 files changed, 82 insertions, 11 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8cb248fb6a68..9d4a1d630d0b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -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++;
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index dcdfcaa12653..1855c6770045 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -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)