Hi Ted, Thanks a lot for your help. For workload #1, indeed, the number of transactions being captured in jdb2 are significantly more than workload #2. Also, the fdatasync() instead of fsync() does help in reducing the time for workload #1. Thanks, Rohan On Sun, 29 Apr 2018 at 12:12, Rohan Kadekodi <kadekodirohan@xxxxxxxxx> wrote: > Hi Ted, > Thanks a lot for your help. For workload #1, indeed, the number of transactions being captured in jdb2 are significantly more than workload #2. Also, the fdatasync() instead of fsync() does help in reducing the time for workload #1. > Thanks, > Rohan > On Sat, 28 Apr 2018 at 20:20, Theodore Y. Ts'o <tytso@xxxxxxx> wrote: >> On Sat, Apr 28, 2018 at 11:24:32AM -0500, Vijay Chidambaram wrote: >> > >> > While we expect workload 1 to take more time than workload 2 since it >> > is extending the file, 10x higher time seems suspicious. If we remove >> > the fsync in workload 1, the running time drops to 3s. If we remove >> > the fsync in workload 2, the running time is around the same (1.5s). >> Can you mount the file system; run workload #N, and then once it's >> done, capture the output of /dev/fs/jbd2/<dev>-8/info, which should >> look like this: >> % cat /proc/fs/jbd2/dm-1-8/info >> 498438 transactions (498366 requested), each up to 65536 blocks >> average: >> 0ms waiting for transaction >> 0ms request delay >> 470ms running transaction >> 0ms transaction was being locked >> 0ms flushing data (in ordered mode) >> 0ms logging transaction >> 2522us average transaction commit time >> 161 handles per transaction >> 14 blocks per transaction >> 15 logged blocks per transaction >> It would be interesting to see this for workload #1 and workload #2. >> I will note that if you were using fdatasync(2) instead of fsync(2) >> for workload #2, there wouldn't be any journal transactions needed by >> the overwrites, and the speed up would be quite expecgted. >> It might be that in the overwrite case, especially if you are using >> 128 byte inodes such that the mtime timestamp has only one second >> granularity, that simply there isn't a need to do many journal >> transactions. >> So you might want to try a workload #3, where the fsync(2) is replaced >> by fdatasync(2), and measure the wall clock time and get the jbd2 info >> information as well. >> Cheers, >> - Ted
