Jens Axboe <jens.axboe@xxxxxxxxxx> writes: > On Wed, Apr 14 2010, Jeff Moyer wrote: >> Hi, >> >> The previous two postings can be found here: >> http://lkml.org/lkml/2010/4/1/344 >> and here: >> http://lkml.org/lkml/2010/4/7/325 >> >> The basic problem is that, when running iozone on smallish files (up to >> 8MB in size) and including fsync in the timings, deadline outperforms >> CFQ by a factor of about 5 for 64KB files, and by about 10% for 8MB >> files. From examining the blktrace data, it appears that iozone will >> issue an fsync() call, and subsequently wait until its CFQ timeslice >> has expired before the journal thread can run to actually commit data to >> disk. >> >> The approach taken to solve this problem is to implement a blk_yield call, >> which tells the I/O scheduler not to idle on this process' queue. The call >> is made from the jbd[2] log_wait_commit function. >> >> This patch set addresses previous concerns that the sync-noidle workload >> would be starved by keeping track of the average think time for that >> workload and using that to decide whether or not to yield the queue. >> >> My testing showed nothing but improvements for mixed workloads, though I >> wouldn't call the testing exhaustive. I'd still very much like feedback >> on the approach from jbd/jbd2 developers. Finally, I will continue to do >> performance analysis of the patches. > > This is starting to look better. Can you share what tests you did? I > tried reproducing with fs_mark last time and could not. Did you use the fs_mark command line I (think I) had posted? What storage were you using? I took Vivek's iostest and modified the mixed workload to do buffered random reader, buffered sequential reader, and buffered writer for all of 1, 2, 4, 8 and 16 threads each. The initial problem was reported against iozone, which can show the problem quite easily when run like so: iozone -s 64 -e -f /mnt/test/iozone.0 -i 0 -+n You can also just run iozone in auto mode, but that can take quite a while to complete. All of my tests for this round have been against a NetApp hardware RAID. I wanted to test against a simple sata disk as well, but have become swamped with other issues. I'll include all of this information in the next patch posting. Sorry about that. Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
