Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 1e3335de authored by Jens Axboe's avatar Jens Axboe Committed by Jens Axboe
Browse files

cfq-iosched: improve preemption for cooperating tasks 



When testing the syslet async io approach, I discovered that CFQ
sometimes didn't perform as well as expected. cfq_should_preempt()
needs to better check for cooperating tasks, so fix that by allowing
preemption of an equal priority queue if the recently queued request
is as good a candidate for IO as the one we are currently waiting for.

Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent b9099ff6

block/cfq-iosched.c

+20 −6
Original line number Diff line number Diff line
@@ -867,15 +867,11 @@ static int cfq_arm_slice_timer(struct cfq_data *cfqd) 


static void cfq_dispatch_insert(request_queue_t *q, struct request *rq)

{

	struct cfq_data *cfqd = q->elevator->elevator_data;

	struct cfq_queue *cfqq = RQ_CFQQ(rq);



	cfq_remove_request(rq);

	cfqq->on_dispatch[rq_is_sync(rq)]++;

	elv_dispatch_sort(q, rq);



	rq = list_entry(q->queue_head.prev, struct request, queuelist);

	cfqd->last_sector = rq->sector + rq->nr_sectors;

}



/*
@@ -1585,6 +1581,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, 
		   struct request *rq)

{

	struct cfq_queue *cfqq = cfqd->active_queue;

	sector_t dist;



	if (cfq_class_idle(new_cfqq))

		return 0;
@@ -1594,14 +1591,14 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, 


	if (cfq_class_idle(cfqq))

		return 1;

	if (!cfq_cfqq_wait_request(new_cfqq))

		return 0;



	/*

	 * if the new request is sync, but the currently running queue is

	 * not, let the sync request have priority.

	 */

	if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))

		return 1;



	/*

	 * So both queues are sync. Let the new request get disk time if

	 * it's a metadata request and the current queue is doing regular IO.
@@ -1609,6 +1606,21 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, 
	if (rq_is_meta(rq) && !cfqq->meta_pending)

		return 1;



	if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))

		return 0;



	/*

	 * if this request is as-good as one we would expect from the

	 * current cfqq, let it preempt

	 */

	if (rq->sector > cfqd->last_sector)

		dist = rq->sector - cfqd->last_sector;

	else

		dist = cfqd->last_sector - rq->sector;



	if (dist <= cfqd->active_cic->seek_mean)

		return 1;



	return 0;

}
@@ -1719,6 +1731,8 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq) 
	cfqq->on_dispatch[sync]--;

	cfqq->service_last = now;



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



	if (!cfq_class_idle(cfqq))

		cfqd->last_end_request = now;