xfs
[Top] [All Lists]

[PATCH 2/9]: Reduce Log I/O latency

To: xfs-oss <xfs@xxxxxxxxxxx>
Subject: [PATCH 2/9]: Reduce Log I/O latency
From: David Chinner <dgc@xxxxxxx>
Date: Thu, 22 Nov 2007 11:33:39 +1100
Cc: lkml <linux-kernel@xxxxxxxxxxxxxxx>
Sender: xfs-bounce@xxxxxxxxxxx
User-agent: Mutt/1.4.2.1i
Reduce log I/O latency

To ensure that log I/O is issued as the highest priority I/O, set
the I/O priority of the log I/O to the highest possible. This will
ensure that log I/O is not held up behind bulk data or other
metadata I/O as delaying log I/O can pause the entire transaction
subsystem. Introduce a new buffer flag to allow us to tag the log
buffers so we can discrimiate when issuing the I/O.

Signed-off-by: Dave Chinner <dgc@xxxxxxx>
---
 fs/xfs/linux-2.6/xfs_buf.c |    3 +++
 fs/xfs/linux-2.6/xfs_buf.h |    5 ++++-
 fs/xfs/xfs_log.c           |    2 ++
 3 files changed, 9 insertions(+), 1 deletion(-)

Index: 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_buf.c
===================================================================
--- 2.6.x-xfs-new.orig/fs/xfs/linux-2.6/xfs_buf.c       2007-11-22 
10:47:21.937396362 +1100
+++ 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_buf.c    2007-11-22 10:53:11.556186722 
+1100
@@ -1255,6 +1255,9 @@ next_chunk:
 
 submit_io:
        if (likely(bio->bi_size)) {
+               /* log I/O should not be delayed by anything. */
+               if (bp->b_flags & XBF_LOG_BUFFER)
+                       bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 
0));
                submit_bio(rw, bio);
                if (size)
                        goto next_chunk;
Index: 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_buf.h
===================================================================
--- 2.6.x-xfs-new.orig/fs/xfs/linux-2.6/xfs_buf.h       2007-11-22 
10:47:21.945395328 +1100
+++ 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_buf.h    2007-11-22 10:53:11.556186722 
+1100
@@ -53,7 +53,8 @@ typedef enum {
        XBF_DELWRI = (1 << 6),  /* buffer has dirty pages                  */
        XBF_STALE = (1 << 7),   /* buffer has been staled, do not find it  */
        XBF_FS_MANAGED = (1 << 8),  /* filesystem controls freeing memory  */
-       XBF_ORDERED = (1 << 11),    /* use ordered writes                  */
+       XBF_LOG_BUFFER = (1 << 9),  /* Buffer issued by the log            */
+       XBF_ORDERED = (1 << 11),    /* use ordered writes                  */
        XBF_READ_AHEAD = (1 << 12), /* asynchronous read-ahead             */
 
        /* flags used only as arguments to access routines */
@@ -340,6 +341,8 @@ extern void xfs_buf_trace(xfs_buf_t *, c
 #define XFS_BUF_TARGET(bp)             ((bp)->b_target)
 #define XFS_BUFTARG_NAME(target)       xfs_buf_target_name(target)
 
+#define XFS_BUF_SET_LOGBUF(bp) ((bp)->b_flags |= XBF_LOG_BUFFER)
+
 static inline int xfs_bawrite(void *mp, xfs_buf_t *bp)
 {
        bp->b_fspriv3 = mp;
Index: 2.6.x-xfs-new/fs/xfs/xfs_log.c
===================================================================
--- 2.6.x-xfs-new.orig/fs/xfs/xfs_log.c 2007-11-22 10:47:21.945395328 +1100
+++ 2.6.x-xfs-new/fs/xfs/xfs_log.c      2007-11-22 10:53:11.556186722 +1100
@@ -1443,6 +1443,8 @@ xlog_sync(xlog_t          *log,
        XFS_BUF_ZEROFLAGS(bp);
        XFS_BUF_BUSY(bp);
        XFS_BUF_ASYNC(bp);
+       XFS_BUF_SET_LOGBUF(bp);
+
        /*
         * Do an ordered write for the log block.
         * Its unnecessary to flush the first split block in the log wrap case.


<Prev in Thread] Current Thread [Next in Thread>