From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755234AbYKDJFB (ORCPT ); Tue, 4 Nov 2008 04:05:01 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753820AbYKDJEZ (ORCPT ); Tue, 4 Nov 2008 04:04:25 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:58604 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753587AbYKDJEW (ORCPT ); Tue, 4 Nov 2008 04:04:22 -0500 Date: Tue, 4 Nov 2008 10:04:05 +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: <20081104090405.GA507@elte.hu> References: <20081104041554.605521183@goodmis.org> <20081104042203.499871423@goodmis.org> <20081104080747.GA27075@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081104080747.GA27075@elte.hu> 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 * Ingo Molnar wrote: > * 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. ... which is exactly what your patch implements :-) > note that preempt-disable will also produce less trace entries, > especially in very irq-rich workloads. Hence it will be "faster". this point still holds. Do we have any good guess about the 'captured trace events per second' rate in the two cases, are they the same? Ingo