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Commit e6c5bc73 authored by Jeff Moyer's avatar Jeff Moyer Committed by Jens Axboe
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cfq: break apart merged cfqqs if they stop cooperating 



cfq_queues are merged if they are issuing requests within the mean seek
distance of one another.  This patch detects when the coopearting stops and
breaks the queues back up.

Signed-off-by: default avatarJeff Moyer <jmoyer@redhat.com>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent b3b6d040

block/cfq-iosched.c

+76 −3
Original line number Diff line number Diff line
@@ -38,6 +38,12 @@ static int cfq_slice_idle = HZ / 125; 
 */

#define CFQ_MIN_TT		(2)



/*

 * Allow merged cfqqs to perform this amount of seeky I/O before

 * deciding to break the queues up again.

 */

#define CFQQ_COOP_TOUT		(HZ)



#define CFQ_SLICE_SCALE		(5)

#define CFQ_HW_QUEUE_MIN	(5)
@@ -116,6 +122,7 @@ struct cfq_queue { 
	u64 seek_total;

	sector_t seek_mean;

	sector_t last_request_pos;

	unsigned long seeky_start;



	pid_t pid;
@@ -1036,6 +1043,11 @@ static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd, 
{

	struct cfq_queue *cfqq;



	if (!cfq_cfqq_sync(cur_cfqq))

		return NULL;

	if (CFQQ_SEEKY(cur_cfqq))

		return NULL;



	/*

	 * We should notice if some of the queues are cooperating, eg

	 * working closely on the same area of the disk. In that case,
@@ -1050,6 +1062,8 @@ static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd, 
	 */

	if (!cfq_cfqq_sync(cfqq))

		return NULL;

	if (CFQQ_SEEKY(cfqq))

		return NULL;



	return cfqq;

}
@@ -1181,7 +1195,7 @@ static int cfqq_process_refs(struct cfq_queue *cfqq) 


static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq)

{

	int process_refs;

	int process_refs, new_process_refs;

	struct cfq_queue *__cfqq;



	/* Avoid a circular list and skip interim queue merges */
@@ -1199,8 +1213,17 @@ static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq) 
	if (process_refs == 0)

		return;



	/*

	 * Merge in the direction of the lesser amount of work.

	 */

	new_process_refs = cfqq_process_refs(new_cfqq);

	if (new_process_refs >= process_refs) {

		cfqq->new_cfqq = new_cfqq;

		atomic_add(process_refs, &new_cfqq->ref);

	} else {

		new_cfqq->new_cfqq = cfqq;

		atomic_add(new_process_refs, &cfqq->ref);

	}

}



/*
@@ -2029,6 +2052,19 @@ cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
	total = cfqq->seek_total + (cfqq->seek_samples/2);

	do_div(total, cfqq->seek_samples);

	cfqq->seek_mean = (sector_t)total;



	/*

	 * If this cfqq is shared between multiple processes, check to

	 * make sure that those processes are still issuing I/Os within

	 * the mean seek distance.  If not, it may be time to break the

	 * queues apart again.

	 */

	if (cfq_cfqq_coop(cfqq)) {

		if (CFQQ_SEEKY(cfqq) && !cfqq->seeky_start)

			cfqq->seeky_start = jiffies;

		else if (!CFQQ_SEEKY(cfqq))

			cfqq->seeky_start = 0;

	}

}



/*
@@ -2391,6 +2427,32 @@ cfq_merge_cfqqs(struct cfq_data *cfqd, struct cfq_io_context *cic, 
	return cic_to_cfqq(cic, 1);

}



static int should_split_cfqq(struct cfq_queue *cfqq)

{

	if (cfqq->seeky_start &&

	    time_after(jiffies, cfqq->seeky_start + CFQQ_COOP_TOUT))

		return 1;

	return 0;

}



/*

 * Returns NULL if a new cfqq should be allocated, or the old cfqq if this

 * was the last process referring to said cfqq.

 */

static struct cfq_queue *

split_cfqq(struct cfq_io_context *cic, struct cfq_queue *cfqq)

{

	if (cfqq_process_refs(cfqq) == 1) {

		cfqq->seeky_start = 0;

		cfqq->pid = current->pid;

		cfq_clear_cfqq_coop(cfqq);

		return cfqq;

	}



	cic_set_cfqq(cic, NULL, 1);

	cfq_put_queue(cfqq);

	return NULL;

}

/*

 * Allocate cfq data structures associated with this request.

 */
@@ -2413,11 +2475,22 @@ cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask) 
	if (!cic)

		goto queue_fail;



new_queue:

	cfqq = cic_to_cfqq(cic, is_sync);

	if (!cfqq || cfqq == &cfqd->oom_cfqq) {

		cfqq = cfq_get_queue(cfqd, is_sync, cic->ioc, gfp_mask);

		cic_set_cfqq(cic, cfqq, is_sync);

	} else {

		/*

		 * If the queue was seeky for too long, break it apart.

		 */

		if (cfq_cfqq_coop(cfqq) && should_split_cfqq(cfqq)) {

			cfq_log_cfqq(cfqd, cfqq, "breaking apart cfqq");

			cfqq = split_cfqq(cic, cfqq);

			if (!cfqq)

				goto new_queue;

		}



		/*

		 * Check to see if this queue is scheduled to merge with

		 * another, closely cooperating queue.  The merging of