linux-kernel - Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)

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Message-Id: <1232455343.4895.4.camel@kulgan.wumi.org.au>
Date:	Tue, 20 Jan 2009 23:12:23 +1030
From:	Kevin Shanahan <kmshanah@...b.org.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Avi Kivity <avi@...hat.com>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Kevin Shanahan <kmshanah@...xo.wumi.org.au>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)

On Tue, 2009-01-20 at 12:35 +0100, Ingo Molnar wrote:
> * Kevin Shanahan <kmshanah@...b.org.au> wrote:
> 
> > On Mon, 2009-01-19 at 22:45 +0100, Rafael J. Wysocki wrote:
> > > This message has been generated automatically as a part of a report
> > > of regressions introduced between 2.6.27 and 2.6.28.
> > > 
> > > The following bug entry is on the current list of known regressions
> > > introduced between 2.6.27 and 2.6.28.  Please verify if it still should
> > > be listed and let me know (either way).
> > > 
> > > 
> > > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=12465
> > > Subject		: KVM guests stalling on 2.6.28 (bisected)
> > > Submitter	: Kevin Shanahan <kmshanah@...b.org.au>
> > > Date		: 2009-01-17 03:37 (3 days old)
> > 
> > Yes, please keep this on the list.
> 
> This only seems to occur under KVM, right? I.e. you tested it with -no-kvm 
> and the problem went away, correct?

Well, the I couldn't make the test conditions identical, but it the
problem didn't occur with the test I was able to do:

  http://marc.info/?l=linux-kernel&m=123228728416498&w=2

> This suggests some sort of KVM-specific problem. Scheduler latencies in 
> the seconds that occur under normal load situations are noticed and 
> reported quickly - and there are no such open regressions currently.

It at least suggests a problem with interaction between the scheduler
and kvm, otherwise reverting that scheduler patch wouldn't have made the
regression go away.

Regards,
Kevin.


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