Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752411AbXKPKsR (ORCPT ); Fri, 16 Nov 2007 05:48:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752338AbXKPKsD (ORCPT ); Fri, 16 Nov 2007 05:48:03 -0500 Received: from smtp-outbound-1.vmware.com ([65.113.40.141]:41076 "EHLO smtp-outbound-1.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752178AbXKPKsC (ORCPT ); Fri, 16 Nov 2007 05:48:02 -0500 Date: Fri, 16 Nov 2007 02:48:01 -0800 From: Micah Dowty To: Ingo Molnar 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: <20071116104801.GA4585@vmware.com> References: <20071110001103.GD16250@vmware.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071116060700.GD16273@elte.hu> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1742 Lines: 45 On Fri, Nov 16, 2007 at 07:07:00AM +0100, Ingo Molnar wrote: > > * Micah Dowty wrote: > > > > I am a bit at a loss as to how this could relate to the patch. This > > > looks like a load balance logic issue that causes the load > > > calculation to go wrong? > > > > 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? Interesting.. here are the kernels I've tested so far, not including the git-bisect run I did between 2.6.19 and 2.6.20: 2.6.17 - 2.6.19 - 2.6.19.7 - 2.6.20 + 2.6.21 + 2.6.22 - 2.6.23.1 + Here a "-" means that the problem does not occur (my test program uses 100% of both CPUs) and a "+" means that the test program leaves one CPU mostly idle. Unless I've made a mistake, 2.6.22 seems like the outlier rather than 2.6.23. Is this inconsistent with the scheduler tick hypothesis? Thanks, --Micah - 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/