Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761077AbZATSno (ORCPT ); Tue, 20 Jan 2009 13:43:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753277AbZATSnf (ORCPT ); Tue, 20 Jan 2009 13:43:35 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:54736 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752767AbZATSne (ORCPT ); Tue, 20 Jan 2009 13:43:34 -0500 Date: Tue, 20 Jan 2009 19:42:49 +0100 From: Ingo Molnar To: Kevin Shanahan Cc: Avi Kivity , "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , Mike Galbraith , bugme-daemon@bugzilla.kernel.org, Peter Zijlstra Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected) Message-ID: <20090120184249.GB5048@elte.hu> References: <1232410363.4768.21.camel@kulgan.wumi.org.au> <20090120113546.GA26571@elte.hu> <1232455343.4895.4.camel@kulgan.wumi.org.au> <4975CBF8.90101@redhat.com> <1232474081.4895.76.camel@kulgan.wumi.org.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1232474081.4895.76.camel@kulgan.wumi.org.au> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1284 Lines: 32 * Kevin Shanahan wrote: > Running the ping test with without apache2 running in the guest: > > --- hermes-old.wumi.org.au ping statistics --- > 900 packets transmitted, 900 received, 0% packet loss, time 902740ms > rtt min/avg/max/mdev = 0.568/3.745/272.558/16.990 ms > > And with apache2 running: > > --- hermes-old.wumi.org.au ping statistics --- > 900 packets transmitted, 900 received, 0% packet loss, time 902758ms > rtt min/avg/max/mdev = 0.625/25.634/852.739/76.586 ms > > In both cases it's quite variable, but the max latency is still not as > bad as when running with the irq chip enabled. So the worst-case ping latency is more than 10 times lower? I'd say this points in the direction of some sort of KVM-internal wakeup/signalling latency that happens if KVM does not deschedule. For example it could be a bug like this: if a guest image runs at 100% CPU time for a long time, IRQ injections might not propagate up until the preemption callbacks run. (but i'm just speculating here) Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/