block, bfq: reduce threshold for detecting command queueing (a3c92560) · Commits · 戴 / test

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:

Paolo Valente <paolo.valente@linaro.org> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

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)

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