From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757231AbYIRSZh (ORCPT ); Thu, 18 Sep 2008 14:25:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755569AbYIRSZ3 (ORCPT ); Thu, 18 Sep 2008 14:25:29 -0400 Received: from pih-relay05.plus.net ([212.159.14.18]:35594 "EHLO pih-relay05.plus.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755329AbYIRSZ2 (ORCPT ); Thu, 18 Sep 2008 14:25:28 -0400 Message-ID: <48D29D11.2030406@yahoo.com> Date: Thu, 18 Sep 2008 19:25:21 +0100 From: Sitsofe Wheeler User-Agent: Thunderbird 2.0.0.16 (Macintosh/20080707) MIME-Version: 1.0 To: Peter Zijlstra CC: Arjan van de Ven , linux-kernel@vger.kernel.org, Ingo Molnar Subject: Re: How how latent should non-preemptive scheduling be? References: <48D17B47.7080704@yahoo.com> <20080917145400.29d1809c@infradead.org> <1221705739.15314.20.camel@lappy.programming.kicks-ass.net> In-Reply-To: <1221705739.15314.20.camel@lappy.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Plusnet-Relay: 461a68c3170553fa5dbf5dbc8a0b2b03 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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).