Messages in this thread Patch in this message | | | Date | Wed, 29 Apr 2009 15:07:40 -0700 | From | Greg KH <> | Subject | [patch 41/58] block: revert part of 18ce3751ccd488c78d3827e9f6bf54e6322676fb |
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2.6.27-stable review patch. If anyone has any objections, please let us know.
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From: Jens Axboe <jens.axboe@oracle.com>
commit 78f707bfc723552e8309b7c38a8d0cc51012e813 upstream.
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; }
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Thanks to Sean.White@APCC.com for tracking down this performance regression and providing a test case.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- fs/buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/buffer.c +++ b/fs/buffer.c @@ -3042,7 +3042,7 @@ int sync_dirty_buffer(struct buffer_head 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);
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