Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754600AbXJ2Wwo (ORCPT ); Mon, 29 Oct 2007 18:52:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752122AbXJ2Wwg (ORCPT ); Mon, 29 Oct 2007 18:52:36 -0400 Received: from gw.goop.org ([64.81.55.164]:50930 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751923AbXJ2Wwg (ORCPT ); Mon, 29 Oct 2007 18:52:36 -0400 Message-ID: <47266431.1010500@goop.org> Date: Mon, 29 Oct 2007 15:52:33 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.5 (X11/20070727) MIME-Version: 1.0 To: Ingo Molnar CC: Zachary Amsden , Glauber de Oliveira Costa , linux-kernel@vger.kernel.org, tglx@linutronix.de, rusty@rustcorp.com.au, --cc@redhat.com, avi@quramnet.com, kvm-devel@lists.sourceforge.net, Glauber de Oliveira Costa , Dan Hecht , Garrett Smith Subject: Re: [PATCH] raise tsc clocksource rating References: <11936994092607-git-send-email-gcosta@redhat.com> <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> <20071029224852.GA27547@elte.hu> In-Reply-To: <20071029224852.GA27547@elte.hu> X-Enigmail-Version: 0.95.4 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1380 Lines: 35 Ingo Molnar wrote: > * Zachary Amsden wrote: > > >> On Mon, 2007-10-29 at 20:10 -0300, Glauber de Oliveira Costa wrote: >> >>> From: Glauber de Oliveira Costa >>> >>> tsc is very good time source (when it does not have drifts, does not >>> change it's frequency, i.e. when it works), so it should have its rating >>> raised to a value greater than, or equal 400. >>> >>> Since it's being a tendency among paravirt clocksources to use values >>> around 400, we should declare tsc as even better: So we use 500. >>> >> Why is the TSC better than a paravirt clocksource? In our case this >> is definitely inaccurate. Paravirt clocksources should be preferred >> to TSC, and both must be made available in hardware for platforms >> which do not support paravirt. >> > > if it's inaccurate why are you exposing it to the guest then? Native > only uses the TSC if it's safe and accurate to do so. > It is used as part of the Xen clocksource as a short term extrapolator, with correction parameters supplied by the hypervisor. It should never be used directly. J - 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/