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block: revert part of 18ce3751cc

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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.White@APCC.com for tracking down this performance
regression and providing a test case.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2009-02-17 13:59:08 +01:00
parent 82eb03cfd8
commit 78f707bfc7
1 changed files with 1 additions and 1 deletions
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2
fs/buffer.c
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@ -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);