Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754075AbXJ2Wl3 (ORCPT ); Mon, 29 Oct 2007 18:41:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752303AbXJ2WlW (ORCPT ); Mon, 29 Oct 2007 18:41:22 -0400 Received: from smtp-outbound-1.vmware.com ([65.113.40.141]:47560 "EHLO smtp-outbound-1.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751925AbXJ2WlW (ORCPT ); Mon, 29 Oct 2007 18:41:22 -0400 Subject: Re: [PATCH] raise tsc clocksource rating From: Zachary Amsden To: Glauber de Oliveira Costa Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, rusty@rustcorp.com.au, jeremy@goop.org, --cc@redhat.com, mingo@elte.hu, avi@quramnet.com, kvm-devel@lists.sourceforge.net, Glauber de Oliveira Costa , Dan Hecht , Garrett Smith In-Reply-To: <11936994092607-git-send-email-gcosta@redhat.com> References: <11936994092607-git-send-email-gcosta@redhat.com> Content-Type: text/plain Date: Mon, 29 Oct 2007 15:42:14 -0700 Message-Id: <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> Mime-Version: 1.0 X-Mailer: Evolution 2.10.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1295 Lines: 28 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. Zach - 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/