From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932765AbXHASkg (ORCPT ); Wed, 1 Aug 2007 14:40:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757499AbXHASk2 (ORCPT ); Wed, 1 Aug 2007 14:40:28 -0400 Received: from one.firstfloor.org ([213.235.205.2]:60674 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761288AbXHASk1 (ORCPT ); Wed, 1 Aug 2007 14:40:27 -0400 Date: Wed, 1 Aug 2007 20:40:26 +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: <20070801184026.GC20713@one.firstfloor.org> References: <11859243121617-git-send-email-clameter@sgi.com> <20070801182611.GB20713@one.firstfloor.org> 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 > It is certainly interesting to compare alternative ways of handling the > instruction streams by various processors or models of processors. Well you have to do a lot more work then to handle instable TSCs then. In particular the frequencies can be different between CPUs, they change (which you can catch with cpufreq notifiers) and during the cpufreq change period they're instable (as in you can't tell for some time which frequency they're currently running at and they might be running immediate frequencies) The current cycles_2_ns() users avoid this problem by not using the TSC in this case, but that might not be an option for you (cpufreq is becoming more and more ubiquitous) Good luck. -Andi