Anytime when we submit some IO from a thread, we must unplug the queue. This patch sets the bit to make sure that the queue won't be plugged when the IO is submitted to the device. Without it, there would be additional 3ms delay. Because this is not high-performance path, we don't have to any tricks with attempting to batch more unplug events. Signed-off-by: Mikulas Patocka --- drivers/md/dm-mpath.c | 1 + 1 file changed, 1 insertion(+) Index: linux-2.6.25.3/drivers/md/dm-mpath.c =================================================================== --- linux-2.6.25.3.orig/drivers/md/dm-mpath.c 2008-05-13 23:05:05.000000000 +0200 +++ linux-2.6.25.3/drivers/md/dm-mpath.c 2008-05-13 23:08:51.000000000 +0200 @@ -393,6 +393,7 @@ static void dispatch_queued_ios(struct m info = dm_get_mapinfo(bio); mpio = info->ptr; + bio->bi_flags |= (1 << BIO_RW_SYNC); r = map_io(m, bio, mpio, 1); if (r < 0) bio_endio(bio, r);