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

Christoph Hellwig
Sat, 06 Sep 2014 23:09:54 -0000

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 at lst.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