Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755309AbXJ2Wpk (ORCPT ); Mon, 29 Oct 2007 18:45:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754816AbXJ2WpP (ORCPT ); Mon, 29 Oct 2007 18:45:15 -0400 Received: from gw.goop.org ([64.81.55.164]:60496 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752983AbXJ2WpN (ORCPT ); Mon, 29 Oct 2007 18:45:13 -0400 Message-ID: <47266276.4030000@goop.org> Date: Mon, 29 Oct 2007 15:45:10 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.5 (X11/20070727) MIME-Version: 1.0 To: Zachary Amsden CC: Glauber de Oliveira Costa , linux-kernel@vger.kernel.org, tglx@linutronix.de, rusty@rustcorp.com.au, --cc@redhat.com, mingo@elte.hu, 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> In-Reply-To: <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> X-Enigmail-Version: 0.95.4 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1619 Lines: 38 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. > > Also, please cc all the paravirt developers on things related to > paravirt, especially things with such broad effect. I think 400 is a > good value for a perfect native clocksource. >400 should be reserved > for super-real (i.e. paravirt) sources that should always be chosen over > a hardware realistic implementation in a virtual environment. > Yes, agreed. The tsc is never the right thing to use if there's a paravirt clocksource available. What's wrong with rating it 300? What inferior clocksource does it lose out to? Shouldn't that clocksource be lowered? (Why don't we just use 1 to 10?) 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/