Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761193AbXFAPxm (ORCPT ); Fri, 1 Jun 2007 11:53:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756299AbXFAPxe (ORCPT ); Fri, 1 Jun 2007 11:53:34 -0400 Received: from viefep18-int.chello.at ([213.46.255.22]:15030 "EHLO viefep14-int.chello.at" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755411AbXFAPxd (ORCPT ); Fri, 1 Jun 2007 11:53:33 -0400 Subject: Re: [PATCH 3/5] lockstat: core infrastructure From: Peter Zijlstra To: Daniel Walker Cc: Ingo Molnar , Steven Rostedt , linux-kernel@vger.kernel.org, Andrew Morton , Jason Baron , Thomas Gleixner In-Reply-To: <1180711606.15884.32.camel@imap.mvista.com> References: <20070529125248.877196281@chello.nl> <20070529130107.112347096@chello.nl> <1180470525.32594.71.camel@imap.mvista.com> <20070530132431.GA23947@elte.hu> <20070530134907.GA27085@elte.hu> <1180544796.32594.184.camel@imap.mvista.com> <1180545380.2958.1.camel@lappy> <1180545913.32594.194.camel@imap.mvista.com> <20070601131249.GA17059@elte.hu> <1180711606.15884.32.camel@imap.mvista.com> Content-Type: text/plain Date: Fri, 01 Jun 2007 17:52:33 +0200 Message-Id: <1180713154.5676.4.camel@lappy> 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: 1862 Lines: 44 On Fri, 2007-06-01 at 08:26 -0700, Daniel Walker wrote: > On Fri, 2007-06-01 at 15:12 +0200, Ingo Molnar wrote: > > * Daniel Walker wrote: > > > > > On Wed, 2007-05-30 at 19:16 +0200, Peter Zijlstra wrote: > > > > > > I think you are mistaken here; the two are similar but not > > > > identical. > > > > > > > > I see sched_clock() as fast first, accurate second. Whereas the > > > > clocksource thing is accurate first, fast second. > > > > > > This is true .. However, if there is a speed different it's small. > > > > Ugh. Have you ever compared pmtimer (or even hpet) against TSC based > > sched_clock()? What you write is so wrong that it's not even funny. You > > keep repeating this nonsense despite having been told multiple times > > that you are dead wrong. > > Yes I have, and your right there is a difference, and a big > difference .. Above I was referring only to the TSC clocksource, since > that's an apples to apples comparison .. I would never compare the TSC > to the acpi_pm, that's no contest .. > > The acpi_pm as sched_clock() with hackbench was about %25 slower, the > pit was 10x slower approximately. (I did this months ago.) The whole issue is that you don't have any control over what clocksource you'll end up with. If it so happens that pmtimer gets selected your whole box will crawl if its used liberaly, like the patch under discussion does. So, having two interfaces, one fast and one accurate is the right answer IMHO. And I agree, that if the arch has a fast clock but doesn't use it for sched_clock() that would be a shortcoming of that arch. - 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/