From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected) Date: Tue, 20 Jan 2009 13:56:52 +0100 Message-ID: <20090120125652.GA1457@elte.hu> References: <1232410363.4768.21.camel@kulgan.wumi.org.au> <20090120113546.GA26571@elte.hu> <1232455343.4895.4.camel@kulgan.wumi.org.au> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <1232455343.4895.4.camel-9TBizaOOD0ujuAshGpSIhRCuuivNXqWP@public.gmane.org> Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Kevin Shanahan Cc: Avi Kivity , "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , Kevin Shanahan , Mike Galbraith , Peter Zijlstra * Kevin Shanahan 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