Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750983AbWERJPj (ORCPT ); Thu, 18 May 2006 05:15:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750985AbWERJPj (ORCPT ); Thu, 18 May 2006 05:15:39 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:46541 "EHLO ecfrec.frec.bull.fr") by vger.kernel.org with ESMTP id S1750983AbWERJPi convert rfc822-to-8bit (ORCPT ); Thu, 18 May 2006 05:15:38 -0400 Subject: Re: rt20 scheduling latency testcase and failure data From: =?ISO-8859-1?Q?S=E9bastien_Dugu=E9?= To: Ingo Molnar Cc: Darren Hart , Lee Revell , lkml , Thomas Gleixner , Mike Galbraith , Steven Rostedt , Florian Schmidt In-Reply-To: <20060518085640.GA5171@elte.hu> References: <200605121924.53917.dvhltc@us.ibm.com> <200605131601.31880.dvhltc@us.ibm.com> <20060515081341.GB24523@elte.hu> <200605151830.23544.dvhltc@us.ibm.com> <1147941862.4996.15.camel@frecb000686> <20060518084722.GA3343@elte.hu> <1147942687.4996.28.camel@frecb000686> <20060518085640.GA5171@elte.hu> Date: Thu, 18 May 2006 11:18:09 +0200 Message-Id: <1147943890.4996.31.camel@frecb000686> Mime-Version: 1.0 X-Mailer: Evolution 2.4.2.1 X-MIMETrack: Itemize by SMTP Server on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 18/05/2006 11:16:54, Serialize by Router on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 18/05/2006 11:18:47, Serialize complete at 18/05/2006 11:18:47 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1397 Lines: 30 On Thu, 2006-05-18 at 10:56 +0200, Ingo Molnar wrote: > * S?bastien Dugu? wrote: > > > > thanks for tracking this down. FYI, the latency of stopping the trace is > > > that expensive because we are copying large amounts of trace data > > > around, to ensure that /proc/latency_trace is always consistent and is > > > updated atomically, and to make sure that we can update the trace from > > > interrupt contexts too - without /proc/latency_trace accesses blocking > > > them. The latency of stopping the trace is hidden from the tracer itself > > > - but it cannot prevent indirect effects such as your app from missing > > > periods, if the periods are in the 5msec range. > > > > > > > Thanks for the explanation, will have to look deeper into the code > > to understand how it works though. > > there's another complexity on SMP: if trace_all_cpus is set then the > per-cpu trace buffers are sorted chronologically as well while the > copying into the current-max-trace-buffer, to produce easier to read > latency_trace output. > Well, that's not the case here, but thanks for the info. S?bastien. - 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/