Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759122AbXKPKqa (ORCPT ); Fri, 16 Nov 2007 05:46:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752500AbXKPKqV (ORCPT ); Fri, 16 Nov 2007 05:46:21 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:48006 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752470AbXKPKqU (ORCPT ); Fri, 16 Nov 2007 05:46:20 -0500 Date: Fri, 16 Nov 2007 11:45:57 +0100 From: Ingo Molnar To: Micah Dowty Cc: Christoph Lameter , Kyle Moffett , Cyrus Massoumi , LKML Kernel , Andrew Morton , Mike Galbraith , Paul Menage , Dmitry Adamushko , Peter Williams Subject: Re: High priority tasks break SMP balancer? Message-ID: <20071116104557.GA5453@elte.hu> References: <2FAA6826-653E-482F-A037-C539BAEEA1DA@mac.com> <20071115191408.GA4914@vmware.com> <20071115202425.GC4914@vmware.com> <20071115213510.GA16079@vmware.com> <20071116024408.GA20322@vmware.com> <20071116060700.GD16273@elte.hu> <20071116091904.GB31219@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071116091904.GB31219@vmware.com> 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=3.1.7-deb -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1391 Lines: 30 * Micah Dowty wrote: > On Fri, Nov 16, 2007 at 07:07:00AM +0100, Ingo Molnar wrote: > > > My best guess is that this has something to do with the timing with > > > which we sample the CPU's instantaneous load when calculating the load > > > averages.. but I still understand only the basics of the scheduler and > > > SMP balancer. All I really know for sure at this point regarding your > > > patch is that git-bisect found it for me. > > > > hm, your code uses timeouts for this, right? The CPU load average that > > is used for SMP load balancing is sampled from the scheduler tick - and > > has been sampled from the scheduler tick for eons. v2.6.23 defaulted to > > a different method but v2.6.24 samples it from the tick again. So my > > guess is, your testcode behave similarly on 2.6.22 too, correct? > > My sample program (and the VMware code which I originally observed > this behaviour with) wakes up frequently using /dev/rtc. > > I know the problem occurs on 2.6.20 and 2.6.23.1. I haven't tried > 2.6.22 yet, but I'll do so as soon as I can. ok, if you see it on .20 then no need to try .22. Ingo - 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/