Commit 45333d5a authored by Aaron Carroll's avatar Aaron Carroll Committed by Jens Axboe
Browse files

cfq-iosched: fix queue depth detection 



CFQ's detection of queueing devices assumes a non-queuing device and detects
if the queue depth reaches a certain threshold.  Under some workloads (e.g.
synchronous reads), CFQ effectively forces a unit queue depth, thus defeating
the detection logic.  This leads to poor performance on queuing hardware,
since the idle window remains enabled.

This patch inverts the sense of the logic: assume a queuing-capable device,
and detect if the depth does not exceed the threshold.

Signed-off-by: default avatarAaron Carroll <aaronc@gelato.unsw.edu.au>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 60540161

block/cfq-iosched.c

+38 −9
Original line number Diff line number Diff line
@@ -39,6 +39,7 @@ static int cfq_slice_idle = HZ / 125; 
#define CFQ_MIN_TT		(2)



#define CFQ_SLICE_SCALE		(5)

#define CFQ_HW_QUEUE_MIN	(5)



#define RQ_CIC(rq)		\

	((struct cfq_io_context *) (rq)->elevator_private)
@@ -86,7 +87,14 @@ struct cfq_data { 


	int rq_in_driver;

	int sync_flight;



	/*

	 * queue-depth detection

	 */

	int rq_queued;

	int hw_tag;

	int hw_tag_samples;

	int rq_in_driver_peak;



	/*

	 * idle window management
@@ -654,15 +662,6 @@ static void cfq_activate_request(struct request_queue *q, struct request *rq) 
	cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",

						cfqd->rq_in_driver);



	/*

	 * If the depth is larger 1, it really could be queueing. But lets

	 * make the mark a little higher - idling could still be good for

	 * low queueing, and a low queueing number could also just indicate

	 * a SCSI mid layer like behaviour where limit+1 is often seen.

	 */

	if (!cfqd->hw_tag && cfqd->rq_in_driver > 4)

		cfqd->hw_tag = 1;



	cfqd->last_position = rq->hard_sector + rq->hard_nr_sectors;

}
@@ -686,6 +685,7 @@ static void cfq_remove_request(struct request *rq) 
	list_del_init(&rq->queuelist);

	cfq_del_rq_rb(rq);



	cfqq->cfqd->rq_queued--;

	if (rq_is_meta(rq)) {

		WARN_ON(!cfqq->meta_pending);

		cfqq->meta_pending--;
@@ -1833,6 +1833,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
{

	struct cfq_io_context *cic = RQ_CIC(rq);



	cfqd->rq_queued++;

	if (rq_is_meta(rq))

		cfqq->meta_pending++;
@@ -1880,6 +1881,31 @@ static void cfq_insert_request(struct request_queue *q, struct request *rq) 
	cfq_rq_enqueued(cfqd, cfqq, rq);

}



/*

 * Update hw_tag based on peak queue depth over 50 samples under

 * sufficient load.

 */

static void cfq_update_hw_tag(struct cfq_data *cfqd)

{

	if (cfqd->rq_in_driver > cfqd->rq_in_driver_peak)

		cfqd->rq_in_driver_peak = cfqd->rq_in_driver;



	if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&

	    cfqd->rq_in_driver <= CFQ_HW_QUEUE_MIN)

		return;



	if (cfqd->hw_tag_samples++ < 50)

		return;



	if (cfqd->rq_in_driver_peak >= CFQ_HW_QUEUE_MIN)

		cfqd->hw_tag = 1;

	else

		cfqd->hw_tag = 0;



	cfqd->hw_tag_samples = 0;

	cfqd->rq_in_driver_peak = 0;

}



static void cfq_completed_request(struct request_queue *q, struct request *rq)

{

	struct cfq_queue *cfqq = RQ_CFQQ(rq);
@@ -1890,6 +1916,8 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq) 
	now = jiffies;

	cfq_log_cfqq(cfqd, cfqq, "complete");



	cfq_update_hw_tag(cfqd);



	WARN_ON(!cfqd->rq_in_driver);

	WARN_ON(!cfqq->dispatched);

	cfqd->rq_in_driver--;
@@ -2200,6 +2228,7 @@ static void *cfq_init_queue(struct request_queue *q) 
	cfqd->cfq_slice[1] = cfq_slice_sync;

	cfqd->cfq_slice_async_rq = cfq_slice_async_rq;

	cfqd->cfq_slice_idle = cfq_slice_idle;

	cfqd->hw_tag = 1;



	return cfqd;

}

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