Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762512AbXFFKTi (ORCPT ); Wed, 6 Jun 2007 06:19:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759385AbXFFKTa (ORCPT ); Wed, 6 Jun 2007 06:19:30 -0400 Received: from charybdis-ext.suse.de ([195.135.221.2]:42238 "EHLO emea5-mh.id5.novell.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1759410AbXFFKT3 convert rfc822-to-8bit (ORCPT ); Wed, 6 Jun 2007 06:19:29 -0400 Message-Id: <4666A677.76E4.0078.0@novell.com> X-Mailer: Novell GroupWise Internet Agent 7.0.2 HP Date: Wed, 06 Jun 2007 12:20:07 +0200 From: "Jan Beulich" To: "Jeremy Fitzhardinge" Cc: "Ingo Molnar" , "Thomas Gleixner" , "Andrew Morton" , "Linus Torvalds" , , "Xen-devel" , "Chris Wright" , "Andi Kleen" , "lkml" Subject: Re: [Xen-devel] [patch 14/33] xen: xen time implementation References: <20070522140941.802382212@goop.org> <20070522141252.030961467@goop.org> <46668EC6.76E4.0078.0@novell.com> <466686E2.4040004@goop.org> In-Reply-To: <466686E2.4040004@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1123 Lines: 25 >> But I think that a clock source can be expected to be >> monotonic anyway, which Xen's interpolation mechanism doesn't >> guarantee across multiple CPUs. (I'm actually beginning to think that >> this might also be the reason for certain test suites occasionally reporting >> timeouts to fire early.) >> > >Does the kernel expect the tsc clocksource to be completely monotonic >across cpus? Any form of cpu-local clocksource is going to have this >problem; I wonder if clocksources can really only be useful if they're >always referring to a single system-wide time reference - seems like a >bit of a limitation. I suppose so - the clock source's rating gets set to zero if it can be predicted that the TSCs aren't all synchronized, which should pretty much exclude the use of this clock source for any other than fallback if there's really nothing else available. Jan - 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/