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

block/bfq-iosched.c

+2 −2
Original line number Diff line number Diff line
@@ -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)