From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756265AbZAVIlj (ORCPT ); Thu, 22 Jan 2009 03:41:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750981AbZAVIlb (ORCPT ); Thu, 22 Jan 2009 03:41:31 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:51803 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750788AbZAVIla (ORCPT ); Thu, 22 Jan 2009 03:41:30 -0500 Date: Thu, 22 Jan 2009 09:41:05 +0100 From: Ingo Molnar To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Andrew Morton , Frederic Weisbecker , Steven Rostedt Subject: Re: [PATCH 1/5] trace: do not disable wake up tracer on output of trace Message-ID: <20090122084105.GD7438@elte.hu> References: <20090121235306.224764198@goodmis.org> <20090121235805.771064570@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090121235805.771064570@goodmis.org> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.1 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.1 required=5.9 tests=BAYES_05 autolearn=no SpamAssassin version=3.2.3 -1.1 BAYES_05 BODY: Bayesian spam probability is 1 to 5% [score: 0.0430] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt wrote: > From: Steven Rostedt > > Impact: fix to erased trace output > > To try not to have the outputing of a trace interfere with the wakeup > tracer, it would disable tracing while the output was printing. But if a > trace had started when it was disabled, it can show a partial trace. To > try to solve this, on closing of the tracer, it would clear the trace > buffer. > > The latency tracers (wakeup and irqsoff) have two buffers. One for > recording and one for holding the max trace that is printed. The > clearing of the trace above should only affect the recording buffer. But > for some reason it would move the erased trace to the print buffer. > Probably due to a race with the closing of the trace and the saving ofhe > max race. hm, that race needs to be fixed then. > The above is all pretty useless, and if the user does not want the > printing of the trace to be traced itself, then the user can manual > disable tracing. This patch removes all the code that tries to keep the > output of the tracer from modifying the trace. printing of the trace should not be traced. I cannot imagine any usage mode where that would be interesting - and i can imagine a ton of cases where users would be confused/distracted by the tracer in essence zapping their measurement by replacing it with some uninteresting 'the tracer itself has wakeup delays' data. auto-disabling latency tracing while the trace is being output is essential. Measurement should never impact the workload that is being measured. We should fix that race instead. Ingo