Re: regression: 100% io-wait with 2.6.24-rcX

Mike Snitzer
2008-01-17T16:12:12Z

On Jan 17, 2008 8:52 AM, Martin Knoblauch <spamtrap@knobisoft.de> wrote:
>
> ----- Original Message ----
> > From: Fengguang Wu <wfg@mail.ustc.edu.cn>
> > To: Martin Knoblauch <knobi@knobisoft.de>
> > Cc: Mike Snitzer <snitzer@gmail.com>; Peter Zijlstra <peterz@infradead.org>; jplatte@naasa.net; Ingo Molnar <mingo@elte.hu>; linux-kernel@vger.kernel.org; "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>; Linus Torvalds <torvalds@linux-foundation.org>
> > Sent: Wednesday, January 16, 2008 1:00:04 PM
> > Subject: Re: regression: 100% io-wait with 2.6.24-rcX
> >
> > On Wed, Jan 16, 2008 at 01:26:41AM -0800, Martin Knoblauch wrote:
> > > > For those interested in using your writeback improvements in
> > > > production sooner rather than later (primarily with ext3); what
> > > > recommendations do you have? Just heavily test our own 2.6.24
> > +
> >
> your
> > > > evolving "close, but not ready for merge" -mm writeback patchset?
> > > >
> > > Hi Fengguang, Mike,
> > >
> > > I can add myself to Mikes question. It would be good to know
> > a
> >
> "roadmap" for the writeback changes. Testing 2.6.24-rcX so far has
> > been
> >
> showing quite nice improvement of the overall writeback situation and
> > it
> >
> would be sad to see this [partially] gone in 2.6.24-final.
> > Linus
> >
> apparently already has reverted "...2250b". I will definitely repeat my
> > tests
> >
> with -rc8. and report.
> >
> > Thank you, Martin. Can you help test this patch on 2.6.24-rc7?
> > Maybe we can push it to 2.6.24 after your testing.
> >
> Hi Fengguang,
>
> something really bad has happened between -rc3 and -rc6. Embarrassingly I did not catch that earlier :-(
>
> Compared to the numbers I posted in http://lkml.org/lkml/2007/10/26/208 , dd1 is now at 60 MB/sec (slight plus), while dd2/dd3 suck the same way as in pre 2.6.24. The only test that is still good is mix3, which I attribute to the per-BDI stuff.
>
> At the moment I am frantically trying to find when things went down. I did run -rc8 and rc8+yourpatch. No difference to what I see with -rc6. Sorry that I cannot provide any input to your patch.
>
> Depressed
> Martin

Martin,

I've backported Peter's perbdi patchset to 2.6.22.x. I can share it
with anyone who might be interested.

As expected, it has yielded 2.6.24-rcX level scaling. Given the test
result matrix you previously posted, 2.6.22.x+perbdi might give you
what you're looking for (sans improved writeback that 2.6.24 was
thought to be providing). That is, much improved scaling with better
O_DIRECT and network throughput. Just a thought...

Unfortunately, my priorities (and computing resources) have shifted
and I won't be able to thoroughly test Fengguang's new writeback patch
on 2.6.24-rc8... whereby missing out on providing
justification/testing to others on _some_ improved writeback being
included in 2.6.24 final.

Not to mention the window for writeback improvement is all but closed
considering the 2.6.24-rc8 announcement's 2.6.24 final release
timetable.

regards,
Mike