Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755668AbZF2VCR (ORCPT ); Mon, 29 Jun 2009 17:02:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751763AbZF2VCJ (ORCPT ); Mon, 29 Jun 2009 17:02:09 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:44414 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751269AbZF2VCI (ORCPT ); Mon, 29 Jun 2009 17:02:08 -0400 Date: Mon, 29 Jun 2009 23:02:06 +0200 From: Ingo Molnar To: Vince Weaver Cc: Peter Zijlstra , Paul Mackerras , linux-kernel@vger.kernel.org, Mike Galbraith Subject: Re: [numbers] perfmon/pfmon overhead of 17%-94% Message-ID: <20090629210206.GB13125@elte.hu> References: <20090624151010.GA12799@elte.hu> <20090627060432.GB16200@elte.hu> <20090627064404.GA19368@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) 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 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1115 Lines: 27 * Vince Weaver wrote: >> If the 5 thousand cycles measurement overhead _still_ matters to >> you under such circumstances then by all means please submit the >> patches to improve it. Despite your claims this is totally >> fixable with the current perfcounters design, Peter outlined the >> steps of how to solve it, you can utilize ptrace if you want to. > > Is it really "totally" fixible? I don't just mean getting the > overhead from ~3000 down to ~100, I mean down to zero. The thing is, not even pfmon gets it down to zero: pfmon -e INSTRUCTIONS_RETIRED --follow-fork --aggregate-results ~/million 1000001 INSTRUCTIONS_RETIRED So ... do you take the hardliner purist view and consider it crap due to that imprecision, or do you take the pragmatist view of also considering the relative relevance of any imperfection? ;-) 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/