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authorJens Axboe <jens.axboe@oracle.com>2009-02-17 13:59:08 +0100
committerJens Axboe <jens.axboe@oracle.com>2009-02-18 10:32:01 +0100
commit78f707bfc723552e8309b7c38a8d0cc51012e813 (patch)
tree67f47d32eac2cb8288a9469b47c1d8cefc6ce42a /block/genhd.c
parent82eb03cfd862a65363fa2826de0dbd5474cfe5e2 (diff)
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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>
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