linux-kernel - Re: [Bugme-new] [Bug 12564] New: poor performance while preprocessing source code

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Date:	Wed, 28 Jan 2009 17:05:06 -0500
From:	Jeff Layton <jlayton@...hat.com>
To:	steven@...s.net
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	bugme-daemon@...zilla.kernel.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Bugme-new] [Bug 12564] New: poor performance while
 preprocessing source code

On Wed, 28 Jan 2009 13:29:42 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> 
> (switched to email.  Please respond via emailed reply-to-all, not via the
> bugzilla web interface).
> 
> On Wed, 28 Jan 2009 11:29:52 -0800 (PST)
> bugme-daemon@...zilla.kernel.org wrote:
> 
> > http://bugzilla.kernel.org/show_bug.cgi?id=12564
> > 
> >            Summary: poor performance while preprocessing source code
> >            Product: IO/Storage
> 
> Thanks for the report.
> 
> >            Version: 2.5
> >      KernelVersion: 2.6.28.2
> >           Platform: All
> >         OS/Version: Linux
> >               Tree: Mainline
> >             Status: NEW
> >           Severity: normal
> >           Priority: P1
> >          Component: Other
> >         AssignedTo: io_other@...nel-bugs.osdl.org
> >         ReportedBy: steven@...s.net
> > 
> > 
> > Latest working kernel version: 2.6.26-rc3
> > Earliest failing kernel version: 2.6.26-rc4 (or 2.6.26-rc3 + patch)
> 
> (huge performance regression in NFS)
>  
> > Distribution: gentoo
> > 
> > Hardware Environment:
> >   Various 32 and 64 bit Intel and AMD machines with various
> > PATA and SATA disks and various network interfaces.
> > 
> > Problem Description:
> >   Here's my situation.  I've recently upgraded the kernels
> > on ~30 computers at work (from 2.6.21 to 2.6.27).  These 
> > computers are used to build and test software we develop.  
> > We speed up the building process using distcc.  However,
> > after the kernel upgrade, the builds are much much slower.
> > The preprocessing stage seems to be at least 10 times
> > slower.
> >   As evidence of this slowdown I am attaching two images created
> > using distccmon-gnome.  Both snapshots were taken shortly 
> > after starting builds in a clean sandbox.  The only difference
> > is the kernel.  "fast.png" was generated while running
> > kernel 2.6.25.20.  "slow.png" was generated with 2.6.26.
> > The light purple sections indicate the preprocessing times
> > for each file.  
> >   This slowdown is observed on both 32 and 64 bit computers
> > and using either gcc or the intel compiler. (The intel compiler
> > builds do not use distcc, but that are also slower.)  Strangely 
> > enough, it's still faster to use an NFS mounted sandbox on a
> > machine with an older kernel than the same sandbox on the local
> > machine with a newer kernel.  (This suggests to me that it
> > is neither a disk or network IO problem.)
> >   I've used git bisect to narrow it down to a single commit:
> > # bad: [b0b539739fe9b7d75002412a787cfdf4efddbc33] NFS: Ensure that 'noac'
> > and/or 'actimeo=0' turn off attribute caching
> 
> And thanks for bisecting it.
> 

It's a pretty small patch. The obvious question is: "What mount options
are you using on your NFS mounts?"


> > This is the first commit after v2.6.26-rc3.  I'm not an
> > experienced git user, so I don't know how to narrow it down
> > further.  Distccmon-gnome snapshots from the bisection
> > process are similar to the ones noted above.
> >   Naturally, I would like the newer kernels to have similar
> > performance to the older kernels.
> >   I will be attaching various items.  Let me know what other 
> > information might be helpful.
> > 
> > Steps to reproduce:
> > distccmon-gnome &
> > # using a makefile setup to use distcc:
> > make -j 5 all
> > # note preprocessing times in distccmon
> > 
> 
> Something I don't understand from this:
> 
> If your normal setup is using distcc then what role does NFS have to
> play?  I mean, distcc kind-of replaces NFS in this workload.
> 
> Perhaps you could briefly describe the topology/data-flow/etc so that
> we can see how NFS could be a bottleneck here?
> 
> Thanks.
> --
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> 


-- 
Jeff Layton <jlayton@...hat.com>
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