Package: linux-2.6
Version: 2.6.26-15
Severity: important
Tags: patch
Phoronix benchmarked kernels from 2.6.24-29:
"When it came to the SQLite performance, a serious performance
regression began with the Linux 2.6.26 kernel and ended with the Linux
2.6.29 release. Normally it required 27~28 seconds to perform 12,500
database insertions using SQLite, but with the Linux 2.6.26 through
2.6.28 kernel releases it took 109 seconds! Fortunately, this regression
is now fixed."
>From 78f707bfc723552e8309b7c38a8d0cc51012e813 Mon Sep 17 00:00:00 2001
From: Jens Axboe <jens.ax...@oracle.com>
Date: Tue, 17 Feb 2009 13:59:08 +0100
Subject: [PATCH] block: revert part of 18ce3751ccd488c78d3827e9f6bf54e6322676fb
The above commit added WRITE_SYNC and switched various places to using
that for committing writes that will be waited upon immediately after
submission. However, this causes a performance regression with AS and CFQ
for ext3 at least, since sync_dirty_buffer() will submit some writes with
WRITE_SYNC while ext3 has sumitted others dependent writes without the sync
flag set. This causes excessive anticipation/idling in the IO scheduler
because sync and async writes get interleaved, causing a big performance
regression for the below test case (which is meant to simulate sqlite
like behaviour).
---- test case ----
int main(int argc, char **argv)
{
int fdes, i;
FILE *fp;
struct timeval start;
struct timeval end;
struct timeval res;
gettimeofday(&start, NULL);
for (i=0; i<ROWS; i++) {
fp = fopen("test_file", "a");
fprintf(fp, "Some Text Data\n");
fdes = fileno(fp);
fsync(fdes);
fclose(fp);
}
gettimeofday(&end, NULL);
timersub(&end, &start, &res);
fprintf(stdout, "time to write %d lines is %ld(msec)\n", ROWS,
(res.tv_sec*1000000 + res.tv_usec)/1000);
return 0;
}
-------------------
Thanks to sean.wh...@apcc.com for tracking down this performance
regression and providing a test case.
Signed-off-by: Jens Axboe <jens.ax...@oracle.com>
---
fs/buffer.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 665d446..62b57e3 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3108,7 +3108,7 @@ int sync_dirty_buffer(struct buffer_head *bh)
if (test_clear_buffer_dirty(bh)) {
get_bh(bh);
bh->b_end_io = end_buffer_write_sync;
- ret = submit_bh(WRITE_SYNC, bh);
+ ret = submit_bh(WRITE, bh);
wait_on_buffer(bh);
if (buffer_eopnotsupp(bh)) {
clear_buffer_eopnotsupp(bh);
--
1.6.2.1
-- System Information:
Debian Release: squeeze/sid
APT prefers testing
APT policy: (900, 'testing'), (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Kernel: Linux 2.6.29-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
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