Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758896Ab1DYT4f (ORCPT ); Mon, 25 Apr 2011 15:56:35 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:43524 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758152Ab1DYT4e (ORCPT ); Mon, 25 Apr 2011 15:56:34 -0400 Date: Mon, 25 Apr 2011 21:55:54 +0200 From: Ingo Molnar To: Andi Kleen Cc: Peter Zijlstra , Stephane Eranian , 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: <20110425195554.GB391@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> <1303564561.2298.62.camel@twins> <20110425194002.GA30576@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110425194002.GA30576@tassilo.jf.intel.com> 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: 1372 Lines: 34 * Andi Kleen wrote: > One example of this we had recently in the kernel: > > function accesses three global objects. Scalability tanks when the test is > run with more CPUs. Now the hit is near the three memory accesses. Which one > is the one that is actually bouncing cache lines? that's not an example - you are still only giving vague, untestable, unverifiable references. You need to give us something specific and reproducible - preferably a testcase. Peter and me are doing lots of scalability work in the core kernel and for most problems i've met it was enough if we knew the function name - the scalability problem is typically very obvious from that point on - and an annotated profile makes it even more obvious. I've never met a situation what you describe, that it was not possible to disambiguate a real SMP bounce - and i've been fixing SMP bounces in the kernel for over ten years. So you really will have to back up your point with an accurate, reproducible testcase - vague statements like the ones you are making i do not accept at face value, sorry. 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/