block: BARRIER request should imply SYNC

PATCH In review Christoph Hellwig 2 participants 2 messages Jun 17, 2010

Subsystems (2)

VFS GFS2 file system

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Christoph Hellwig

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2010-06-17 06:54 UTC #0 lore raw

PATCH 1/1 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 <[email protected]>

include/linux/fs.h +2 -2

Index: linux-2.6/include/linux/fs.h
===================================================================
@@ -136,7 +136,7 @@ struct inodes_stat_t {
  * SWRITE_SYNC
  * SWRITE_SYNC_PLUG	Like WRITE_SYNC/WRITE_SYNC_PLUG, but locks the buffer.
  *			See SWRITE.
- * WRITE_BARRIER	Like WRITE, but tells the block layer that all
+ * WRITE_BARRIER	Like WRITE_SYNC, but tells the block layer that all
  *			previously submitted writes must be safely on storage
  *			before this one is started. Also guarantees that when
  *			this write is complete, it itself is also safely on

@@ -159,7 +159,7 @@ struct inodes_stat_t {
 #define SWRITE_SYNC_PLUG	\
 			(SWRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))
 #define SWRITE_SYNC	(SWRITE_SYNC_PLUG | (1 << BIO_RW_UNPLUG))
-#define WRITE_BARRIER	(WRITE | (1 << BIO_RW_BARRIER))
+#define WRITE_BARRIER	(WRITE_SYNC | (1 << BIO_RW_BARRIER))
 
 /*
  * These aren't really reads or writes, they pass down information about

fs/gfs2/log.c +1 -1

Index: linux-2.6/fs/gfs2/log.c
===================================================================
@@ -595,7 +595,7 @@ static void log_write_header(struct gfs2
 	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);

Jens Axboe

2010-06-17 07:34 UTC #1 lore raw

Quoted 5 lines · Christoph Hellwig

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.

Quoted 7 lines

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.

Thanks Christoph, applied.

Signature · 1 line

Jens Axboe