[Cluster-devel] gfs2 write bandwidth regression on 6.4-rc3 compareto 5.15.y

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> Hi Wang Yugui,
> 
> On Sun, May 28, 2023 at 5:53?PM Wang Yugui <wangyugui@e16-tech.com> wrote:
> > Hi,
> >
> > > Hi,
> > >
> > > gfs2 write bandwidth regression on 6.4-rc3 compare to 5.15.y.
> > >
> > > we added  linux-xfs@ and linux-fsdevel@ because some related problem[1]
> > > and related patches[2].
> > >
> > > we compared 6.4-rc3(rather than 6.1.y) to 5.15.y because some related patches[2]
> > > work only for 6.4 now.
> > >
> > > [1] https://lore.kernel.org/linux-xfs/20230508172406.1CF3.409509F4 at e16-tech.com/
> > > [2] https://lore.kernel.org/linux-xfs/20230520163603.1794256-1-willy at infradead.org/
> > >
> > >
> > > test case:
> > > 1) PCIe3 SSD *4 with LVM
> > > 2) gfs2 lock_nolock
> > >     gfs2 attr(T) GFS2_AF_ORLOV
> > >    # chattr +T /mnt/test
> > > 3) fio
> > > fio --name=global --rw=write -bs=1024Ki -size=32Gi -runtime=30 -iodepth 1
> > > -ioengine sync -zero_buffers=1 -direct=0 -end_fsync=1 -numjobs=1 \
> > >       -name write-bandwidth-1 -filename=/mnt/test/sub1/1.txt \
> > >       -name write-bandwidth-2 -filename=/mnt/test/sub2/1.txt \
> > >       -name write-bandwidth-3 -filename=/mnt/test/sub3/1.txt \
> > >       -name write-bandwidth-4 -filename=/mnt/test/sub4/1.txt
> > > 4) patches[2] are applied to 6.4-rc3.
> > >
> > >
> > > 5.15.y result
> > >       fio WRITE: bw=5139MiB/s (5389MB/s),
> > > 6.4-rc3 result
> > >       fio  WRITE: bw=2599MiB/s (2725MB/s)
> >
> > more test result:
> >
> > 5.17.0  WRITE: bw=4988MiB/s (5231MB/s)
> > 5.18.0  WRITE: bw=5165MiB/s (5416MB/s)
> > 5.19.0  WRITE: bw=5511MiB/s (5779MB/s)
> > 6.0.5   WRITE: bw=3055MiB/s (3203MB/s), WRITE: bw=3225MiB/s (3382MB/s)
> > 6.1.30  WRITE: bw=2579MiB/s (2705MB/s)
> >
> > so this regression  happen in some code introduced in 6.0,
> > and maybe some minor regression in 6.1 too?
> 
> thanks for this bug report. Bob has noticed a similar looking
> performance regression recently, and it turned out that commit
> e1fa9ea85ce8 ("gfs2: Stop using glock holder auto-demotion for now")
> inadvertently caused buffered writes to fall back to writing single
> pages instead of multiple pages at once. That patch was added in
> v5.18, so it doesn't perfectly align with the regression history
> you're reporting, but maybe there's something else going on that we're
> not aware of.
> 
> In any case, the regression introduced by commit e1fa9ea85ce8 should
> be fixed by commit c8ed1b359312 ("gfs2: Fix duplicate
> should_fault_in_pages() call"), which ended up in v6.5-rc1.
> 
> Could you please check where we end up with that fix?

I applied c8ed1b359312 on 6.1.36.
# the build/test of 6.5-rc1 is yet not ready.

fio performance result:
  WRITE: bw=2683MiB/s (2813MB/s)

but  the performance of fio 'Laying out IO file' is improved.
Jobs: 4 (f=4): [F(4)][100.0%][w=5168MiB/s][w=5168 IOPS][eta 00m:00s]

so there seems 2 problems,  one is fixed by c8ed1b359312.
but another is still left.

Best Regards
Wang Yugui (wangyugui at e16-tech.com)
2023/07/11