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Commit 4dab46ff authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Jens Axboe
Browse files

xen/blkfront: use tagged queuing for barriers 



When barriers are supported, then use QUEUE_ORDERED_TAG to tell the block
subsystem that it doesn't need to do anything else with the barriers.
Previously we used ORDERED_DRAIN which caused the block subsystem to
drain all pending IO before submitting the barrier, which would be
very expensive.

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
parent e96f6abe

drivers/block/xen-blkfront.c

+13 −4
Original line number Diff line number Diff line
@@ -420,9 +420,19 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size) 
static int xlvbd_barrier(struct blkfront_info *info)

{

	int err;

	unsigned ordered = QUEUE_ORDERED_NONE;



	err = blk_queue_ordered(info->rq,

				info->feature_barrier ? QUEUE_ORDERED_DRAIN : QUEUE_ORDERED_NONE);

	/*

	 * If we don't have barrier support, then there's really no

	 * way to guarantee write ordering, so we really just have to

	 * send writes to the backend and hope for the best.  If

	 * barriers are supported then we can treat them as proper

	 * ordering tags.

	 */

	if (info->feature_barrier)

		ordered = QUEUE_ORDERED_TAG;



	err = blk_queue_ordered(info->rq, ordered);



	if (err)

		return err;
@@ -509,7 +519,6 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity, 
	info->rq = gd->queue;

	info->gd = gd;



	if (info->feature_barrier)

	xlvbd_barrier(info);



	if (vdisk_info & VDISK_READONLY)