From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751761AbWGZS7N (ORCPT ); Wed, 26 Jul 2006 14:59:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751764AbWGZS7N (ORCPT ); Wed, 26 Jul 2006 14:59:13 -0400 Received: from mail.suse.de ([195.135.220.2]:29840 "EHLO mx1.suse.de") by vger.kernel.org with ESMTP id S1751761AbWGZS7L (ORCPT ); Wed, 26 Jul 2006 14:59:11 -0400 From: Andi Kleen To: discuss@x86-64.org Subject: Re: [discuss] Re: [PATCH] Allow all Opteron processors to change pstate at same time Date: Wed, 26 Jul 2006 20:53:40 +0200 User-Agent: KMail/1.9.3 Cc: "Langsdorf, Mark" , "Gulam, Nagib" , linux-kernel@vger.kernel.org, cpufreq@lists.linux.org.uk References: <84EA05E2CA77634C82730353CBE3A84303218F09@SAUSEXMB1.amd.com> In-Reply-To: <84EA05E2CA77634C82730353CBE3A84303218F09@SAUSEXMB1.amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200607262053.40123.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > In contrast, the same machine running with TSC and standard > PN! sees massive drift, upwards of an hour, within an hour. Do you see the same drift when you lock date on a single CPU with taskset? > If the TSCnow! patch reduces measured drift down to a second > a week, would you consider that acceptable? No because even one second a week will break timing badly over time. I believe the only good solution unless hardware helps would be to use per CPU TSC offsets as discussed earlier. Even that is a bit risky because there can be still very small drifts, but they should be limited by a clock tick error max and might work out. -Andi