Commit a3c92560 authored by Paolo Valente's avatar Paolo Valente Committed by Jens Axboe

block, bfq: reduce threshold for detecting command queueing

bfq simple heuristic from cfq for detecting whether the drive performs
command queueing: check whether the average number of in-flight requests
is above a given threshold. Unfortunately this heuristic does fail to
detect queueing (on drives with queueing) if processes doing I/O are few
and issue I/O with a low depth.

To reduce false negatives, this commit lowers the threshold.
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9dee8b3b
......@@ -230,7 +230,7 @@ static struct kmem_cache *bfq_pool;
#define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
/* hw_tag detection: parallel requests threshold and min samples needed. */
#define BFQ_HW_QUEUE_THRESHOLD 4
#define BFQ_HW_QUEUE_THRESHOLD 3
#define BFQ_HW_QUEUE_SAMPLES 32
#define BFQQ_SEEK_THR (sector_t)(8 * 100)
......@@ -4798,7 +4798,7 @@ static void bfq_update_hw_tag(struct bfq_data *bfqd)
* sum is not exact, as it's not taking into account deactivated
* requests.
*/
if (bfqd->rq_in_driver + bfqd->queued < BFQ_HW_QUEUE_THRESHOLD)
if (bfqd->rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD)
return;
if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
......
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