Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753505AbXJ2XNS (ORCPT ); Mon, 29 Oct 2007 19:13:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752558AbXJ2XNH (ORCPT ); Mon, 29 Oct 2007 19:13:07 -0400 Received: from smtp-outbound-1.vmware.com ([65.113.40.141]:56403 "EHLO smtp-outbound-1.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752350AbXJ2XNF (ORCPT ); Mon, 29 Oct 2007 19:13:05 -0400 Subject: Re: [PATCH] raise tsc clocksource rating From: Zachary Amsden To: Ingo Molnar Cc: Glauber de Oliveira Costa , linux-kernel@vger.kernel.org, tglx@linutronix.de, rusty@rustcorp.com.au, jeremy@goop.org, --cc@redhat.com, avi@quramnet.com, kvm-devel@lists.sourceforge.net, Glauber de Oliveira Costa , Dan Hecht , Garrett Smith In-Reply-To: <20071029230213.GA1982@elte.hu> References: <11936994092607-git-send-email-gcosta@redhat.com> <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> <20071029224852.GA27547@elte.hu> <1193698505.9793.90.camel@bodhitayantram.eng.vmware.com> <20071029230213.GA1982@elte.hu> Content-Type: text/plain Date: Mon, 29 Oct 2007 16:13:58 -0700 Message-Id: <1193699638.9793.97.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: 1339 Lines: 31 On Tue, 2007-10-30 at 00:02 +0100, Ingo Molnar wrote: > * Zachary Amsden wrote: > > Not every guest support paravirt, but for correctness, all guests > > require TSC, which must be exposed all the way up to userspace, no > > matter what the efficiency or accuracy may be. > > but if there's a perfect TSC available (there is such hardware) then the > TSC _is_ the best clocksource. Paravirt now turns it off unconditionally > in essence. No, if no paravirt clocksource is detected, nothing can override the perfect TSC hardware clocksource rating of 400. And if a paravirt clocksource is detected, it is always better than TSC. > anyway, that's at most an optimization issue. No strong feelings here, > and we can certainly delay this patch until this gets all sorted out. This patch should be nacked, since it is just wrong. This is not an optimization issue. It is an accuracy issue for all virtualization environments that affects long term kernel clock stability, which is important to fix, and the best way to do that is to use a paravirt clocksource. 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/