On Wed, 2017-12-13 at 15:14 -0500, Jeff Layton wrote: > On Wed, 2017-12-13 at 10:05 -0500, J. Bruce Fields wrote: > > This is great, thanks. > > > > On Wed, Dec 13, 2017 at 09:19:58AM -0500, Jeff Layton wrote: > > > With this, we reduce inode metadata updates across all 3 filesystems > > > down to roughly the frequency of the timestamp granularity, particularly > > > when it's not being queried (the vastly common case). > > > > > > The pessimal workload here is 1 byte writes, and it helps that > > > significantly. Of course, that's not what we'd consider a real-world > > > workload. > > > > > > A tiobench-example.fio workload also shows some modest performance > > > gains, and I've gotten mails from the kernel test robot that show some > > > significant performance gains on some microbenchmarks (case-msync-mt in > > > the vm-scalability testsuite to be specific), with an earlier version of > > > this set. > > > > > > With larger writes, the gains with this patchset mostly vaporize, > > > but it does not seem to cause performance to regress anywhere, AFAICT. > > > > > > I'm happy to run other workloads if anyone can suggest them. > > > > > > At this point, the patchset works and does what it's expected to do in > > > my own testing. It seems like it's at least a modest performance win > > > across all 3 major disk-based filesystems. It may also encourage others > > > to implement i_version as well since it reduces the cost. > > > > Do you have an idea what the remaining cost is? > > > > Especially in the ext4 case, are you still able to measure any > > difference in performance between the cases where i_version is turned on > > and off, after these patches? > > Attached is a fio jobfile + the output from 3 different runs using it > with ext4. This one is using 4k writes. There was no querying of > i_version during the runs. I've done several runs with each and these > are pretty representative of the results: > > old = 4.15-rc3, i_version enabled > ivers = 4.15-rc3 + these patches, i_version enabled > noivers = 4.15-rc3 + these patches, i_version disabled > > To snip out the run status lines: > > old: > WRITE: bw=85.6MiB/s (89.8MB/s), 9994KiB/s-11.1MiB/s (10.2MB/s-11.7MB/s), io=50.2GiB (53.8GB), run=600001-600001msec > > ivers: > WRITE: bw=110MiB/s (115MB/s), 13.5MiB/s-14.2MiB/s (14.1MB/s-14.9MB/s), io=64.3GiB (69.0GB), run=600001-600001msec > > noivers: > WRITE: bw=117MiB/s (123MB/s), 14.2MiB/s-15.2MiB/s (14.9MB/s-15.9MB/s), io=68.7GiB (73.8GB), run=600001-600001msec > > So, I see some performance degradation with -o iversion compared to not > having it enabled (maybe due to the extra atomic fetches?), but this set > erases most of the difference. > > > > > > > [1]: On ext4 it must be turned on with the i_version mount option, > > > mostly due to fears of incurring this impact, AFAICT. > > > > So xfs and btrfs both have i_version updates on by default at this > > point? (Assuming the filesystem's created with recent enough tools, > > etc.) > > > > Yes. With xfs and btrfs, I don't think you can disable it these days. > ...and for completeness, I'm seeing better performance with 4k writes on xfs with this set as well: old: WRITE: bw=86.7MiB/s (90.0MB/s), 9689KiB/s-11.7MiB/s (9921kB/s-12.2MB/s), io=50.8GiB (54.6GB), run=600001-600002msec new: WRITE: bw=129MiB/s (136MB/s), 15.8MiB/s-16.6MiB/s (16.6MB/s-17.4MB/s), io=75.9GiB (81.5GB), run=600001-600001msec btrfs doesn't show much change ... it's possible that that patch isn't quite right: old: WRITE: bw=49.1MiB/s (51.5MB/s), 5656KiB/s-7011KiB/s (5792kB/s-7179kB/s), io=28.8GiB (30.9GB), run=600001-600003msec new: WRITE: bw=50.3MiB/s (52.7MB/s), 5753KiB/s-7264KiB/s (5891kB/s-7438kB/s), io=29.5GiB (31.6GB), run=600001-600002msec This is with the kernel running in a KVM guest, virtio disk in guest backed by a LVM volume on a bog-standard ssd. Performance characteristics could be different on a different setup, but I think this is encouraging. Note that this patchset requires some prerequisite patches that Andrew is carrying. The complete series is here for anyone who wants to play with it: https://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux.git/log/?h=iversion -- Jeff Layton