From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932129AbXGFVED (ORCPT ); Fri, 6 Jul 2007 17:04:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760067AbXGFVDy (ORCPT ); Fri, 6 Jul 2007 17:03:54 -0400 Received: from tomts25-srv.bellnexxia.net ([209.226.175.188]:53801 "EHLO tomts25-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759907AbXGFVDx (ORCPT ); Fri, 6 Jul 2007 17:03:53 -0400 Date: Fri, 6 Jul 2007 17:03:51 -0400 From: Mathieu Desnoyers To: "Li, Tong N" Cc: Andi Kleen , Andrew Morton , Alexey Dobriyan , linux-kernel@vger.kernel.org Subject: Re: [patch 10/10] Scheduler profiling - Use immediate values Message-ID: <20070706210351.GA13491@Krystal> References: <20070706200325.GD8174@one.firstfloor.org> <5FD5754DDBA0B1499B5A0B4BB5419485015CC9E1@fmsmsx411.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <5FD5754DDBA0B1499B5A0B4BB5419485015CC9E1@fmsmsx411.amr.corp.intel.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 17:03:27 up 5 days, 15:46, 4 users, load average: 0.03, 0.20, 0.24 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Li, Tong N (tong.n.li@intel.com) wrote: > > I found that memory latency is difficult to measure in modern x86 > > CPUs because they have very clever prefetchers that can often > > outwit benchmarks. > > A pointer-chasing program that accesses a random sequence of addresses > usually can produce a good estimate on memory latency. Also, prefetching > can be turned off in BIOS or by modifying the MSRs. > > > Another trap on P4 is that RDTSC is actually quite slow and > synchronizes > > the CPU; that can add large measurement errors. > > > > -Andi > > The cost can be amortized if the portion of memory accesses is long > enough. > > tong > That's what I am currently doing.. the results are coming in a few moments... :) -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68