Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754796AbXJ3HUC (ORCPT ); Tue, 30 Oct 2007 03:20:02 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753001AbXJ3HTy (ORCPT ); Tue, 30 Oct 2007 03:19:54 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:47052 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752734AbXJ3HTx (ORCPT ); Tue, 30 Oct 2007 03:19:53 -0400 Date: Tue, 30 Oct 2007 08:19:19 +0100 From: Ingo Molnar To: Ian Pratt Cc: Jeremy Fitzhardinge , Zachary Amsden , Glauber de Oliveira Costa , linux-kernel@vger.kernel.org, tglx@linutronix.de, rusty@rustcorp.com.au, Avi Kivity , kvm-devel@lists.sourceforge.net, Glauber de Oliveira Costa , Dan Hecht , Garrett Smith Subject: Re: [PATCH] raise tsc clocksource rating Message-ID: <20071030071919.GB17074@elte.hu> References: <11936994092607-git-send-email-gcosta@redhat.com> <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> <20071029224852.GA27547@elte.hu> <47266431.1010500@goop.org> <20071029225528.GA31293@elte.hu> <47266A00.4040408@goop.org> <20071029232140.GA10518@elte.hu> <8A87A9A84C201449A0C56B728ACF491E34C5F5@liverpoolst.ad.cl.cam.ac.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8A87A9A84C201449A0C56B728ACF491E34C5F5@liverpoolst.ad.cl.cam.ac.uk> User-Agent: Mutt/1.5.16 (2007-06-09) 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=3.1.7-deb -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1442 Lines: 34 * Ian Pratt wrote: > > > Sigh, I don't really want to have this fight again. > > > > i dont remember us having discussed this before, ever. If there's any > > "fight" about monotonicity and SMP then it would be a pretty onesided > > affair, with you being beaten up seriously ;-) > > Actually, it is possible, even for NUMA systems with CPUs running off > completely different oscillators, and in the presence of CPU frequency > changes, power management, and even in the presence of thermal > throttling (though the latter introduces temporary inaccuracies it > doesn't affect monotonicity or rate). > > Take a look at the Xen code to see how each physical CPU is > independently calibrated on an ongoing basis, how movement of VCPUs > between physical CPUs is tracked, and how shared variables are used to > ensure montonicity if a guest requires it. I think that's wishful thinking. Check out: http://people.redhat.com/mingo/time-warp-test/time-warp-test.c change TEST_TSC to 0, run it on an SMP guest (on a reasonably fast machine) and let me know whether you can make SMP guests not come up with monotonicity violations in the CLOCK tests. 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/