From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757388AbYISIoh (ORCPT ); Fri, 19 Sep 2008 04:44:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751016AbYISIo2 (ORCPT ); Fri, 19 Sep 2008 04:44:28 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:34030 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750868AbYISIo0 (ORCPT ); Fri, 19 Sep 2008 04:44:26 -0400 Date: Fri, 19 Sep 2008 10:44:12 +0200 From: Ingo Molnar To: Sitsofe Wheeler Cc: Peter Zijlstra , Arjan van de Ven , linux-kernel@vger.kernel.org, Steven Rostedt Subject: Re: How how latent should non-preemptive scheduling be? Message-ID: <20080919084412.GD17592@elte.hu> References: <48D17B47.7080704@yahoo.com> <20080917145400.29d1809c@infradead.org> <1221705739.15314.20.camel@lappy.programming.kicks-ass.net> <48D29D11.2030406@yahoo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <48D29D11.2030406@yahoo.com> 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 * Sitsofe Wheeler wrote: > Peter Zijlstra wrote: >> What you can do to investigate this, is use the sched_wakeup tracer from >> ftrace, that should give a function trace of the highest wakeup latency >> showing what the kernel is doing. > > I struggled to find documentation of ftrace because it's quite new. I > have come across > http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_MRG/1.0/html/Realtime_Tuning_Guide/sect-Realtime_Tuning_Guide-Realtime_Specific_Tuning-Using_the_ftrace_Utility_for_Tracing_Latencies.html > and > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/ftrace.txt;h=d330fe3103da9c9a3cb8f888ac7255ce48e666d4;hb=45e9c0de2e86485f8b6633fd64ab19cfbff167f6 > . > > Thanks to those I started up the debugfs filesystem and went to the > trace directories but the on tracers in available_tracers are > ftrace sched_switch none > > I can't see anything in the code that would disable wakeup... Any ideas > on what might be wrong? I'm using a 2.6.27rc6 kernel. here's two quick howtos: http://redhat.com/~mingo/sched-devel.git/readme-tracer.txt http://redhat.com/~mingo/sched-devel.git/howto-trace-latencies.txt you need to enable: CONFIG_SCHED_TRACER=y CONFIG_CONTEXT_SWITCH_TRACER=y it's not particularly well named though. Why doesnt it say LATENCY_TRACER or something? > Additionally I think I found a trigger - unplugging the power cable > from the EeePC and having it run on battery seems to then set off this > periodic stall every 30 seconds... There's no CPU frequency scaling > enabled either (Celeron M's seemingly don't have P states and support > for cpufreq is configured out). sounds like potential SMM triggered latencies. Ingo