On Thu, Dec 22, 2016 at 09:42:04AM -0500, Jeff Layton wrote: > On Thu, 2016-12-22 at 00:45 -0800, Christoph Hellwig wrote: > > On Wed, Dec 21, 2016 at 12:03:17PM -0500, Jeff Layton wrote: > > > > > > Only btrfs, ext4, and xfs implement it for data changes. Because of > > > this, these filesystems must log the inode to disk whenever the > > > i_version counter changes. That has a non-zero performance impact, > > > especially on write-heavy workloads, because we end up dirtying the > > > inode metadata on every write, not just when the times change. [1] > > > > Do you have numbers to justify these changes? > > I have numbers. As to whether they justify the changes, I'm not sure. > This helps a lot on a (admittedly nonsensical) 1-byte write workload. On > XFS, with this fio jobfile: To me, the interesting question is whether this allows us to turn on i_version updates by default on xfs and ext4. When Josef looked at doing that previously he withdrew the patch due to performance regressions. I think the most useful thread started here: http://lkml.kernel.org/r/1337092396-3272-1-git-send-email-josef@xxxxxxxxxx Skimming quickly.... I think the regression was also in the small-write case. So apparently that was thought to reveal a real problem? So if you've mostly eliminated that regression, then that's good motivation for your patches. (Though I think in addition to comparing the patched and unpatched i_version case, we need to compare to the unpatched not-i_version case. I'm not clear whether you did that.) --b. > > --------------------8<------------------ > [global] > direct=0 > size=2g > filesize=512m > bsrange=1-1 > timeout=60 > numjobs=1 > directory=/mnt/scratch > > [f1] > filename=randwrite > rw=randwrite > --------------------8<------------------ > > Unpatched kernel: > WRITE: io=7707KB, aggrb=128KB/s, minb=128KB/s, maxb=128KB/s, mint=60000msec, maxt=60000msec > > Patched kernel: > WRITE: io=12701KB, aggrb=211KB/s, minb=211KB/s, maxb=211KB/s, mint=60000msec, maxt=60000msec > > So quite a difference there and it's pretty consistent across runs. If I > change the jobfile to have "direct=1" and "bsrange=4k-4k", then any > variation between the two doesn't seem to be significant (numbers vary > as much between runs on the same kernels and are roughly the same). > > Playing with buffered I/O sizes between 1 byte and 4k shows that as the > I/O sizes get larger, this makes less difference (which is what I'd > expect). > > Previous testing with ext4 shows roughly the same results. btrfs shows > some benefit here but significantly less than with ext4 or xfs. Not sure > why that is yet -- maybe CoW effects? > > That said, I don't have a great test rig for this. I'm using VMs with a > dedicated LVM volume that's on a random SSD I had laying around. It > could use testing on a wider set of configurations and workloads. > > I was also hoping that others may have workloads that they think might > be (postively or negatively) affected by these changes. If you can think > of any in particular, then I'm interested to hear about them. > > -- > Jeff Layton <jlayton@xxxxxxxxxx> > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html
