Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932828AbXKOUYf (ORCPT ); Thu, 15 Nov 2007 15:24:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762023AbXKOUY1 (ORCPT ); Thu, 15 Nov 2007 15:24:27 -0500 Received: from smtp-outbound-1.vmware.com ([65.113.40.141]:55306 "EHLO smtp-outbound-1.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751665AbXKOUY0 (ORCPT ); Thu, 15 Nov 2007 15:24:26 -0500 Date: Thu, 15 Nov 2007 12:24:25 -0800 From: Micah Dowty To: Christoph Lameter Cc: Kyle Moffett , Cyrus Massoumi , LKML Kernel , Ingo Molnar , Andrew Morton , Mike Galbraith , Paul Menage Subject: Re: High priority tasks break SMP balancer? Message-ID: <20071115202425.GC4914@vmware.com> References: <20071109223417.GB16250@vmware.com> <4734F397.7080802@gmx.net> <20071110001103.GD16250@vmware.com> <2FAA6826-653E-482F-A037-C539BAEEA1DA@mac.com> <20071115191408.GA4914@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: 1265 Lines: 27 On Thu, Nov 15, 2007 at 12:07:47PM -0800, Christoph Lameter wrote: > On Thu, 15 Nov 2007, Micah Dowty wrote: > > > For reference, the exact test I used with git-bisect is attached. The > > C program (priosched) starts two busy-looping threads and a > > high-priority high-frequency thread which uses relatively little > > CPU. The Python program repeatedly starts the C program, runs it for a > > half second, and measures the resulting imbalance in CPU usage. On > > kernels prior to the above commit, this reports values within about > > 10% of 1.0. On later kernels, it crashes within a couple iterations > > due to a divide-by-zero error :) > > The kernel crashes? Sounds like your application crashes with a divide by > zero? Yes, the Python test harness crashes, not the kernel. It's just because on a kernel which exhibits this SMP balancer bug, within a couple of test iterations I'll hit a case where cpu1 was almost totally idle and the test harness divides by zero when calculating the imbalance. --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/