Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758883Ab1DYTqD (ORCPT ); Mon, 25 Apr 2011 15:46:03 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:44679 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758152Ab1DYTqB (ORCPT ); Mon, 25 Apr 2011 15:46:01 -0400 Date: Mon, 25 Apr 2011 21:45:42 +0200 From: Ingo Molnar To: Stephane Eranian Cc: Dehao Chen , Andi Kleen , Peter Zijlstra , arun@sharma-home.net, Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, Lin Ming , Arnaldo Carvalho de Melo , Thomas Gleixner , eranian@gmail.com, Arun Sharma , Linus Torvalds , Andrew Morton Subject: Re: [generalized cache events] Re: [PATCH 1/1] perf tools: Add missing user space support for config1/config2 Message-ID: <20110425194542.GA391@elte.hu> References: <20110422165007.GA18401@vps.sharma-home.net> <20110422203022.GA20573@elte.hu> <20110422203222.GA21219@elte.hu> <20110423000347.GC9328@tassilo.jf.intel.com> <1303545012.2298.44.camel@twins> <20110424021907.GB3019@alboin.amr.corp.intel.com> <20110425174110.GB28239@elte.hu> <20110425180528.GA30724@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes 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: 1300 Lines: 30 * Stephane Eranian wrote: > > This certainly does not match the results i'm seeing on real applications, > > using "-e instructions:pp" PEBS+LBR profiling. How do you explain that? > > Also, can you demonstrate your claim with a real example? > > LBR removes the off-by-1 IP problem, it does not remove the shadow effect, > i.e., that blind spot of N cycles caused by the PEBS arming mechanism. I really think you are grasping at straws here - unless you are able to demonstrate clear problems - which you have failed to do so far. The pure act of profiling probably disturbs a typical workload statistically more than a few cycles skew of the period. I could imagine artifacts with realy short periods and artificially short and dominant hotpaths - but in those cases the skew does not matter much in practice: a short and dominant hotpath is pinpointed very easily ... So i really think it's a non-issue in practice - but you can certainly prove me wrong by demonstrating whatever problems you suspect. Thanks, 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/