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
