From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756307AbYGRKg1 (ORCPT ); Fri, 18 Jul 2008 06:36:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753832AbYGRKgT (ORCPT ); Fri, 18 Jul 2008 06:36:19 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:44392 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752976AbYGRKgT (ORCPT ); Fri, 18 Jul 2008 06:36:19 -0400 Date: Fri, 18 Jul 2008 12:35:59 +0200 From: Ingo Molnar To: Steven Rostedt Cc: Linus Torvalds , linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [git pull] tracing fixes Message-ID: <20080718103559.GA4368@elte.hu> References: <20080717173210.GA12828@elte.hu> <20080718084152.GJ6875@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080718084152.GJ6875@elte.hu> User-Agent: Mutt/1.5.18 (2008-05-17) 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 * Ingo Molnar wrote: > > > CFLAGS_REMOVE_sched_clock.o = -pg > > > +CFLAGS_REMOVE_sched.o = -mno-spe -pg > > > endif > > > > > > > Ingo, > > > > Why not trace the scheduler functions? I found a lot of useful > > information from seeing what functions are being called (namely the > > latencies caused by the fair scheduler balancing). Not being able to > > trace sched.c seems to keep a lot of useful data from being accessed. > > i agree in general, but it was causing lockups with: > > http://redhat.com/~mingo/misc/config-Thu_Jul_17_13_34_52_CEST_2008 > > note the MAXSMP in the config which sets NR_CPUS to 4096: > > CONFIG_NR_CPUS=4096 > > our randconfig testing stumbled on it. That is a debug helper to "tune > up the kernel for as large systems as possible" and can bring in > regressions not normally seen. ok, figured it out today: the lockups were due to the NMI watchdog and a missing NMI protection in cpu_clock(). I've reactivated the topic that solves this problem area and it all works fine now. the sched.o change probably made a difference just because it reduced the cross section between the NMI watchdog and the scheduler, making lockups less likely during the ftrace self-test. I'll revert it once the tracing/nmisafe is upstream. Ingo