block: BARRIER request should imply SYNC

A barrier request should by defintion have priority in get_request
and let the queue be unplugged immediately as it's blocking all forward
progress due to the queue draining.

Most filesystems already get this implicitly by the way how submit_bh
treats the buffer_ordered flag, and gfs2 sets it explicitly.  But btrfs
and XFS are still forgetting to set the flag, as is blkdev_issue_flush
and some places in DM/MD.

For XFS on metadata heavy workloads this gives a consistent speedup
in the 2-3% range.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 6a857e24f947..efc3539ac5a1 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -595,7 +595,7 @@ static void log_write_header(struct gfs2_sbd *sdp, u32 flags, int pull)
         if (test_bit(SDF_NOBARRIERS, &sdp->sd_flags))
                 goto skip_barrier;
         get_bh(bh);
-        submit_bh(WRITE_SYNC | (1 << BIO_RW_BARRIER) | (1 << BIO_RW_META), bh);
+        submit_bh(WRITE_BARRIER | (1 << BIO_RW_META), bh);
         wait_on_buffer(bh);
         if (buffer_eopnotsupp(bh)) {
                 clear_buffer_eopnotsupp(bh);