linux-kernel - [PATCH] virtio_blk: merge S/G list entries by default

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Date:	Sat,  6 Sep 2014 16:09:54 -0700
From:	Christoph Hellwig <hch@....de>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: [PATCH] virtio_blk: merge S/G list entries by default

Most virtio setups have a fairly limited number of ring entries available.
Enable S/G entry merging by default to fit into less of them.  This restores
the behavior at time of the virtio-blk blk-mq conversion, which was changed
by commit "block: add queue flag for disabling SG merging" which made the
behavior optional, but didn't update the existing drivers to keep their
previous behavior.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 drivers/block/virtio_blk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 0a58140..311b857 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -634,7 +634,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 	vblk->tag_set.ops = &virtio_mq_ops;
 	vblk->tag_set.queue_depth = virtblk_queue_depth;
 	vblk->tag_set.numa_node = NUMA_NO_NODE;
-	vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
+	vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
 	vblk->tag_set.cmd_size =
 		sizeof(struct virtblk_req) +
 		sizeof(struct scatterlist) * sg_elems;
-- 
1.9.1

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