Hello, this is a third iteration of my series improving handling of sync syscall. Since previous submission I have changed ordering of patches and split some patches as Christoph suggested. I have run three tests below to verify performance impact of the patch series. Each test has been run with 1, 2, and 4 filesystems mounted; test with 2 filesystems was run with each filesystem on a different disk, test with 4 filesystems had 2 filesystems on the first disk and 2 filesystems on the second disk. Test 1: Run 200 times sync with filesystem mounted to verify overhead of sync when there are no data to write. Test 2: For each filesystem run a process creating 40 KB files, sleep for 3 seconds, run sync. Test 3: For each filesystem run a process creating 20 GB file, sleep for 5 seconds, run sync. I have performed 10 runs of each test for xfs, ext3, ext4, and btrfs filesystems. Results of test 1 ----------------- Numbers are time it took 200 syncs to complete. Character in braces is + if the time increased with 2*STDDEV reliability, - if it decreased with 2*STDDEV reliability, 0 otherwise. BASE PATCHED FS AVG STDDEV AVG STDDEV xfs, 1 disks 4.189300 0.051525 2.141300 0.063389 (-) xfs, 2 disks 4.820600 0.019096 4.611400 0.066322 (-) xfs, 4 disks 6.518300 1.440362 6.435700 0.510641 (0) ext4, 1 disks 4.085000 0.011375 1.689500 0.001360 (-) ext4, 2 disks 4.088100 0.006488 1.705000 0.026359 (-) ext4, 4 disks 4.107300 0.011934 1.702900 0.001814 (-) ext3, 1 disks 4.080200 0.009527 1.703400 0.030559 (-) ext3, 2 disks 4.138300 0.143909 1.694000 0.001414 (-) ext3, 4 disks 4.107200 0.002482 1.702900 0.007778 (-) btrfs, 1 disks 11.214600 0.086619 8.737200 0.081076 (-) btrfs, 2 disks 32.910000 0.162089 30.673400 0.538820 (-) btrfs, 4 disks 67.987700 1.655654 67.247100 1.971887 (0) So we see nice improvements almost all over the board. Results of test 2 ----------------- Numbers are time it took sync to complete. BASE PATCHED FS AVG STDDEV AVG STDDEV xfs, 1 disks 0.436000 0.012000 0.506000 0.014283 (+) xfs, 2 disks 1.105000 0.055543 1.274000 0.244426 (0) xfs, 4 disks 5.880000 2.997135 4.837000 3.875448 (0) ext4, 1 disks 0.791000 0.055579 0.853000 0.042438 (0) ext4, 2 disks 18.232000 13.505638 17.254000 2.000506 (0) ext4, 4 disks 491.790000 218.565229 696.783000 234.933562 (0) ext3, 1 disks 15.315000 2.065465 1.900000 0.184662 (-) ext3, 2 disks 128.524000 18.090519 55.278000 1.530554 (-) ext3, 4 disks 221.202000 30.090432 232.849000 68.745423 (0) btrfs, 1 disks 0.452000 0.026000 0.494000 0.023749 (0) btrfs, 2 disks 5.156000 4.530852 4.083000 1.560519 (0) btrfs, 4 disks 31.154000 11.220828 36.987000 17.334126 (0) Except for ext3 which got a nice boost here and XFS which seems to be a tad bit slower, there are no changes that would stand out of the noise. Results of test 3 ----------------- Numbers are time it took sync to complete. BASE PATCHED FS AVG STDDEV AVG STDDEV xfs, 1 disks 12.083000 0.058660 10.898000 0.285475 (-) xfs, 2 disks 20.182000 0.549614 14.977000 0.351114 (-) xfs, 4 disks 35.814000 5.318310 28.452000 3.332281 (0) ext4, 1 disks 32.956000 5.753789 20.865000 3.892098 (0) ext4, 2 disks 34.922000 3.051966 27.411000 2.752978 (0) ext4, 4 disks 44.508000 6.829004 28.360000 2.561437 (0) ext3, 1 disks 23.475000 1.288885 17.116000 0.319631 (-) ext3, 2 disks 43.508000 4.998647 41.547000 2.597976 (0) ext3, 4 disks 92.130000 11.344117 79.362000 9.891208 (0) btrfs, 1 disks 12.478000 0.394304 12.847000 0.171117 (0) btrfs, 2 disks 15.030000 0.777817 18.014000 2.011418 (0) btrfs, 4 disks 32.395000 4.248859 38.411000 3.179939 (0) Here we see XFS and ext3 had some improvements, ext4 likely as well although the results are relatively noisy. Out of curiosity, I also tried removing syncfs(sb, 0) call from the sync sequence altogether as Christoph suggested. In the test 1, results end up being even better, tests 2 and 3 end up roughly the same, sometimes slightly better. I also performed tests where we write some amount of data to the filesystem and then call sync - there were no changes in sync times that would stand out of the noise. So this might be a worthwhile simplification of sync... Honza -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
