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author | Jens Axboe <jens.axboe@oracle.com> | 2009-02-17 13:59:08 +0100 |
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committer | Jens Axboe <jens.axboe@oracle.com> | 2009-02-18 10:32:01 +0100 |
commit | 78f707bfc723552e8309b7c38a8d0cc51012e813 (patch) | |
tree | 67f47d32eac2cb8288a9469b47c1d8cefc6ce42a /scripts | |
parent | 82eb03cfd862a65363fa2826de0dbd5474cfe5e2 (diff) |
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.White@APCC.com for tracking down this performance
regression and providing a test case.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'scripts')
0 files changed, 0 insertions, 0 deletions