Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758742Ab1DYSF7 (ORCPT ); Mon, 25 Apr 2011 14:05:59 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:57577 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754005Ab1DYSF6 (ORCPT ); Mon, 25 Apr 2011 14:05:58 -0400 Date: Mon, 25 Apr 2011 20:05:28 +0200 From: Ingo Molnar To: Dehao Chen Cc: Andi Kleen , Peter Zijlstra , arun@sharma-home.net, Stephane Eranian , 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: <20110425180528.GA30724@elte.hu> References: <20110422105211.GB1948@elte.hu> <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> 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: 1146 Lines: 26 * Dehao Chen wrote: > > ... and the resulting low level of noise in the average period length is > > what matters. The instruction itself will still be one of the hotspot > > instructions, statistically. > > Not true. This skid will lead to some aggregation and shadow effects on some > certain instructions. To make things worse, these effects are deterministic > and cannot be removed by either sampling for multiple times or by averaging > among instructions within a basic block. As a result, some actual "hot spot" > are not sampled at all. You can simply try to collect a basic block level > CPI, and you'll get a very misleading profile. 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? 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/