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

Ingo Molnar
2009-01-20T12:56:52Z

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

> > 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.

the scheduler affects almost everything, so almost by definition a
scheduler change can tickle a race or other timing bug in just about any
code - and reverting that change in the scheduler can make the bug go
away. But yes, it could also be a genuine scheduler bug - that is always a
possibility.

Could you please run a cfs-debug-info.sh session on a CONFIG_SCHED_DEBUG=y
and CONFIG_SCHEDSTATS=y kernel, while you are experiencing those
latencies:

http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh

and post that (relatively large) somewhere, or send it as a reply after
bzip2 -9 compressing it? It will include a lot of information about the
delays your tasks are experiencing.

Ingo