Re: [linus:master] [block] e70c301fae: stress-ng.aiol.ops_per_sec 49.6% regression

Oliver Sang
2025-01-07T08:26:37Z

hi, Christoph Hellwig,

On Fri, Jan 03, 2025 at 07:49:25AM +0100, Christoph Hellwig wrote:
> On Thu, Jan 02, 2025 at 10:49:41AM +0100, Niklas Cassel wrote:
> > > > from below information, it seems an 'ahci' to me. but since I have limited
> > > > knowledge about storage driver, maybe I'm wrong. if you want more information,
> > > > please let us know. thanks a lot!
> > >
> > > Yes, this looks like ahci. Thanks a lot!
> >
> > Did this ever get resolved?
> >
> > I haven't seen a patch that seems to address this.
> >
> > AHCI (ata_scsi_queuecmd()) only issues a single command, so if there is any
> > reordering when issuing a batch of commands, my guess is that the problem
> > also affects SCSI / the problem is in upper layers above AHCI, i.e. SCSI lib
> > or block layer.
>
> I started looking into this before the holidays. blktrace shows perfectly
> sequential writes without any reordering using ahci, directly on the
> block device or using xfs and btrfs when using dd. I also started
> looking into what the test does and got as far as checking out the
> stress-ng source tree and looking at stress-aiol.c. AFAICS the default
> submission does simple reads and writes using increasing offsets.
> So if the test result isn't a fluke either the aio code does some
> weird reordering or btrfs does.
>
> Oliver, did the test also show any interesting results on non-btrfs
> setups?
>

I tried to run with ext4 fs [1] and xfs [2], seems not be able to get stable
results (%stddev is too big, even bigger than %change). seems no value from
both tests.

[1]
=========================================================================================
compiler/cpufreq_governor/disk/fs/kconfig/nr_threads/rootfs/tbox_group/test/testcase/testtime:
gcc-12/performance/1HDD/ext4/x86_64-rhel-9.4/100%/debian-12-x86_64-20240206.cgz/lkp-icl-2sp8/aiol/stress-ng/60s

a3396b99990d8b4e e70c301faece15b618e54b613b1
---------------- ---------------------------
%stddev %change %stddev
\ | \
142.01 ± 17% -4.6% 135.55 ± 18% stress-ng.aiol.async_I/O_events_completed_per_sec
14077 ± 14% -3.3% 13617 ± 15% stress-ng.aiol.ops
233.95 ± 14% -3.4% 225.97 ± 15% stress-ng.aiol.ops_per_sec

[2]
=========================================================================================
compiler/cpufreq_governor/disk/fs/kconfig/nr_threads/rootfs/tbox_group/test/testcase/testtime:
gcc-12/performance/1HDD/xfs/x86_64-rhel-9.4/100%/debian-12-x86_64-20240206.cgz/lkp-icl-2sp8/aiol/stress-ng/60s

a3396b99990d8b4e e70c301faece15b618e54b613b1
---------------- ---------------------------
%stddev %change %stddev
\ | \
11.97 ± 21% +18.5% 14.19 ± 44% stress-ng.aiol.async_I/O_events_completed_per_sec
1498 ± 33% +9.5% 1640 ± 49% stress-ng.aiol.ops
23.45 ± 34% +10.2% 25.85 ± 52% stress-ng.aiol.ops_per_sec