Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755552AbXJ3MB0 (ORCPT ); Tue, 30 Oct 2007 08:01:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752491AbXJ3MBS (ORCPT ); Tue, 30 Oct 2007 08:01:18 -0400 Received: from mx1.redhat.com ([66.187.233.31]:36622 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752378AbXJ3MBS (ORCPT ); Tue, 30 Oct 2007 08:01:18 -0400 Message-ID: <47271D4A.8030707@redhat.com> Date: Tue, 30 Oct 2007 10:02:18 -0200 From: Glauber de Oliveira Costa User-Agent: Thunderbird 2.0.0.6 (X11/20070811) MIME-Version: 1.0 To: Zachary Amsden CC: Ingo Molnar , 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 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> <1193698505.9793.90.camel@bodhitayantram.eng.vmware.com> <20071029230213.GA1982@elte.hu> <1193699638.9793.97.camel@bodhitayantram.eng.vmware.com> In-Reply-To: <1193699638.9793.97.camel@bodhitayantram.eng.vmware.com> X-Enigmail-Version: 0.95.3 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: 1637 Lines: 41 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Zachary Amsden escreveu: > 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. Why always? tsc is the best possible alternative the _platform_ can provide. So the paravirt clocksource will be at best, as good as tsc. And if it is the case: why bother with communication mechanisms of all kinds, calculations, etc, if we can just read the tsc? Noting again: If the tsc does not arrive accurate to the guest, it will fail the tsc clocksource tests. So it will be rated zero anyway -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (GNU/Linux) Comment: Using GnuPG with Remi - http://enigmail.mozdev.org iD8DBQFHJx1KjYI8LaFUWXMRAv0hAJ4sj0Z1FraYrgbU5Mj0pWOJGk6jtwCfc5xL jpTC273X0oqPTCR7NcVHJOI= =WPzV -----END PGP SIGNATURE----- - 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/