Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750978AbXBMRUV (ORCPT ); Tue, 13 Feb 2007 12:20:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750993AbXBMRUV (ORCPT ); Tue, 13 Feb 2007 12:20:21 -0500 Received: from one.firstfloor.org ([213.235.205.2]:41453 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750978AbXBMRUT (ORCPT ); Tue, 13 Feb 2007 12:20:19 -0500 From: Andi Kleen To: Christoph Lameter Subject: Re: [patch 4/9] Remove the TSC synchronization on SMP machines Date: Tue, 13 Feb 2007 18:20:14 +0100 User-Agent: KMail/1.9.5 Cc: Arjan van de Ven , Vojtech Pavlik , Jiri Bohac , linux-kernel@vger.kernel.org, ssouhlal@freebsd.org, tglx@linutronix.de, johnstul@us.ibm.com, zippel@linux-m68k.org, andrea@suse.de References: <20070201095952.589234000@jet.suse.cz> <1171348808.12771.19.camel@laptopd505.fenrus.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200702131820.15180.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1229 Lines: 28 On Tuesday 13 February 2007 18:09, Christoph Lameter wrote: > On Tue, 13 Feb 2007, Arjan van de Ven wrote: > > > no quite the opposite. gettimeofday() currently is NOT monotonic > > unfortunately. With this patchseries it actually has a better chance of > > becoming that... > > It is monotonic on IA64 at least and we have found that subtle application > bugs occur if it is not. IA64 (and other arches using time interpolation) > can insure the monotoneity of time sources. Are you sure about this? I > wonder why the new time of day subsystem does not have that? Just to avoid spreading misinformation: modulo some new broken hardware (which we always try to work around when found) i386/x86-64 gettimeofday is monotonic. AFAIK on the currently known hardware it should be generally ok. However ntpd can always screw you up, but that's inherent in the design. Safer in general is to use clock_gettime(CLOCK_MONOTONIC, ...) which guarantees no interference from ntpd -Andi - 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/