From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759255AbXHAS0Y (ORCPT ); Wed, 1 Aug 2007 14:26:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753455AbXHAS0P (ORCPT ); Wed, 1 Aug 2007 14:26:15 -0400 Received: from one.firstfloor.org ([213.235.205.2]:60436 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753430AbXHAS0O (ORCPT ); Wed, 1 Aug 2007 14:26:14 -0400 Date: Wed, 1 Aug 2007 20:26:11 +0200 From: Andi Kleen To: Christoph Lameter Cc: Andi Kleen , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/7] Simple Performance Counters: x86_64 support Message-ID: <20070801182611.GB20713@one.firstfloor.org> References: <11859243121617-git-send-email-clameter@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > But then the numbers are not comparable across systems. That would only matter if you're interested in absolute system performance of different systems. But comparable performance testing in general only makes sense when you only change one variable: either you change the hardware or you change the software. If you change both at the same time you'll never know where the difference comes from. I assume this facility is aimed at software performance testing: this means it doesn't make much sense to compare numbers between different systems; just relative numbers on the same system with different software. If you want absolute comparable system performance benchmarks I don't think micro-instrumenting the kernel is a good approach. But for relative performance cycles are fine. Anyways if you really wanted to do ns it's possible too, but far more complicated to do correctly. -Andi