Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764568AbXEYSXz (ORCPT ); Fri, 25 May 2007 14:23:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763353AbXEYSXr (ORCPT ); Fri, 25 May 2007 14:23:47 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:48584 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752417AbXEYSXr (ORCPT ); Fri, 25 May 2007 14:23:47 -0400 Subject: Re: [patch] i386, numaq: enable TSCs again From: john stultz To: Dave Hansen Cc: Ingo Molnar , William Lee Irwin III , Andi Kleen , Satyam Sharma , Andrew Morton , linux-kernel@vger.kernel.org, Peter Zijlstra In-Reply-To: <1180116978.14844.69.camel@localhost.localdomain> References: <20070525073158.GB8094@one.firstfloor.org> <20070525073957.GA15207@elte.hu> <20070525074316.GA16821@elte.hu> <20070525074915.GA18400@elte.hu> <20070525075446.GA20140@elte.hu> <20070525080827.GA22399@elte.hu> <20070525081944.GZ31925@holomorphy.com> <20070525083153.GA27236@elte.hu> <20070525083813.GA19966@holomorphy.com> <20070525084115.GA29077@elte.hu> <1180116978.14844.69.camel@localhost.localdomain> Content-Type: text/plain Date: Fri, 25 May 2007 11:23:26 -0700 Message-Id: <1180117406.6345.4.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1532 Lines: 35 On Fri, 2007-05-25 at 11:16 -0700, Dave Hansen wrote: > On Fri, 2007-05-25 at 10:41 +0200, Ingo Molnar wrote: > > * William Lee Irwin III wrote: > > > > yes, that's what i meant under 'slightly async'. Some AMD CPUs are > > > > like that too and sched_clock() now handles that fine. So we should > > > > try my patch. > > > > > > Sorry, then. I took slight to mean something else. In any event I was > > > only quantifying things. I've no opinion whatsoever on the impact of > > > the code on NUMA-Q, only some recall of its operating characteristics. > > > > there's no need to apologize at all! Thanks for reminding us about the > > time-scale and nature of the TSC drift on NUMAQ. I was worried that > > maybe the TSC was totally unusable for some reason - but that's > > fortunately not the case. So we now have one quirk less, hopefully :-) > > Last I remember, it was totally useless for timekeeping, but was useful > for cpu-local time measurements. > > John, it's still useless for time, right? Does sched_clock() really fix > it? Yea, on multi-node NUMAQ the TSC shouldn't be used for timekeeping. However it should be fine for sched_clock(), or other cpu-local measurements as the TSCs are constant (no cpufreq, no deep sleep states). -john - 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/