On Thu, Apr 15 2010, Jeff Moyer wrote: > 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? No, I didn't see any references to example command lines. I tested on a few single disks, rotating and SSD. I expected the single spinning disk to show the problem to some extent at least, but there was no difference observed with 64kb blocks. > 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. No problem, I'll try the above. -- Jens Axboe -- 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
