From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754544AbYKDII1 (ORCPT ); Tue, 4 Nov 2008 03:08:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753379AbYKDIIT (ORCPT ); Tue, 4 Nov 2008 03:08:19 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:54121 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753371AbYKDIIS (ORCPT ); Tue, 4 Nov 2008 03:08:18 -0500 Date: Tue, 4 Nov 2008 09:07:47 +0100 From: Ingo Molnar To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Andrew Morton , Steven Rostedt Subject: Re: [PATCH 3/3] ftrace: function tracer with irqs disabled Message-ID: <20081104080747.GA27075@elte.hu> References: <20081104041554.605521183@goodmis.org> <20081104042203.499871423@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081104042203.499871423@goodmis.org> 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,DNS_FROM_SECURITYSAGE autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] 0.0 DNS_FROM_SECURITYSAGE RBL: Envelope sender in blackholes.securitysage.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt wrote: > Running hackbench 3 times with the irqs disabled and 3 times with > the preempt disabled function tracer yielded: > > tracing type times entries recorded > ------------ -------- ---------------- > irq disabled 43.393 166433066 > 43.282 166172618 > 43.298 166256704 > > preempt disabled 38.969 159871710 > 38.943 159972935 > 39.325 161056510 your numbers might be correct, but i found that hackbench is not reliable boot-to-boot - it can easily produce 10% systematic noise or more. (perhaps depending on how the various socket data structures happen to be allocated) the really conclusive way to test this would be to add a hack that either does preempt disable or irqs disable, depending on a runtime flag - and then observe how hackbench performance reacts to the value of that flag. note that preempt-disable will also produce less trace entries, especially in very irq-rich workloads. Hence it will be "faster". Ingo