Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751087AbWERI4r (ORCPT ); Thu, 18 May 2006 04:56:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751120AbWERI4r (ORCPT ); Thu, 18 May 2006 04:56:47 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:16864 "EHLO mx3.mail.elte.hu") by vger.kernel.org with ESMTP id S1751087AbWERI4r (ORCPT ); Thu, 18 May 2006 04:56:47 -0400 Date: Thu, 18 May 2006 10:56:40 +0200 From: Ingo Molnar To: =?iso-8859-1?Q?S=E9bastien_Dugu=E9?= Cc: Darren Hart , Lee Revell , lkml , Thomas Gleixner , Mike Galbraith , Steven Rostedt , Florian Schmidt Subject: Re: rt20 scheduling latency testcase and failure data Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1147942687.4996.28.camel@frecb000686> User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=AWL autolearn=no SpamAssassin version=3.0.3 0.0 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1236 Lines: 27 * 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. Ingo - 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/