From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752477AbXLKIn6 (ORCPT ); Tue, 11 Dec 2007 03:43:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750986AbXLKInv (ORCPT ); Tue, 11 Dec 2007 03:43:51 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:54162 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750829AbXLKInu (ORCPT ); Tue, 11 Dec 2007 03:43:50 -0500 Date: Tue, 11 Dec 2007 09:43:24 +0100 From: Ingo Molnar To: Arjan van de Ven Cc: Guillaume Chazarain , Stefano Brivio , Andrew Morton , rjw@sisk.pl, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org Subject: Re: 2.6.24-rc4-git5: Reported regressions from 2.6.23 Message-ID: <20071211084324.GC20172@elte.hu> References: <200712080340.49546.rjw@sisk.pl> <20071210204212.GA5502@elte.hu> <20071210125923.37bd2f10.akpm@linux-foundation.org> <20071210224508.GB27178@elte.hu> <20071210230425.GA641@elte.hu> <20071211003433.5cf0230d@morte> <20071210155611.512ab381@laptopd505.fenrus.org> <20071211010125.75e2e807@inria.fr> <20071210170650.0026ad01@laptopd505.fenrus.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071210170650.0026ad01@laptopd505.fenrus.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Arjan van de Ven wrote: > > That sounds like a big problem. > > it'll get way worse going forward. (but even on todays systems, the > tsc no longer represents frequency, but is some fixed clock totally > unrelated to cpu frequency) X86_FEATURE_CONSTANT_TSC CPUs (all modern Intel CPUs) should be fine - we dont do any TSC frequency fixups for them. The loops_per_jiffy fixup looks like this: if (!(freq->flags & CPUFREQ_CONST_LOOPS)) cpu_data(freq->cpu).loops_per_jiffy = cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new); i.e. X86_FEATURE_CONSTANT_TSC excluded. The sched_clock() scaling factor is modified like this: if (!(freq->flags & CPUFREQ_CONST_LOOPS)) { tsc_khz = cpu_khz; preempt_disable(); set_cyc2ns_scale(cpu_khz, smp_processor_id()); so here X86_FEATURE_CONSTANT_TSC is excluded again. So the whole frequency scaling issue will become a pure legacy issue only with time. Ingo