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

Ingo Molnar
2009-01-20T11:35:46Z

* Kevin Shanahan <kmshanah-biM/RbsGxha6c6uEtOJ/EA@public.gmane.org> 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-biM/RbsGxha6c6uEtOJ/EA@public.gmane.org>
> > 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?

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.

Avi, can you reproduce these latencies? A possibly theory would be some
sort of guest wakeup problem/race triggered by a shift in
preemption/scheduling patterns. Or something related to preempt-notifiers
(which KVM is using). A genuine scheduler bug is in the cards too, but the
KVM-only angle of this bug gives it a low probability.

Ingo