From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 2 Oct 2001 17:34:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 2 Oct 2001 17:34:04 -0400 Received: from [194.213.32.137] ([194.213.32.137]:10500 "EHLO bug.ucw.cz") by vger.kernel.org with ESMTP id ; Tue, 2 Oct 2001 17:33:50 -0400 Date: Mon, 1 Oct 2001 09:28:50 +0000 From: Pavel Machek To: "Grover, Andrew" Cc: "'Alan Cox'" , torvalds@transmeta.com, padraig@antefacto.com, linux-kernel@vger.kernel.org Subject: Re: CPU frequency shifting "problems" Message-ID: <20011001092850.A35@toy.ucw.cz> In-Reply-To: <8FB7D6BCE8A2D511B88C00508B68C2081971D8@orsmsx102.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0.1i In-Reply-To: <8FB7D6BCE8A2D511B88C00508B68C2081971D8@orsmsx102.jf.intel.com>; from andrew.grover@intel.com on Thu, Sep 27, 2001 at 06:24:56PM -0700 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! > > > For example, the Intel "SpeedStep" CPU's are completely broken under > > > Linux, and real-time will advance at different speeds in DC > > and AC modes, > > > because Intel actually changes the frequency of the TSC > > _and_ they don't > > > document how to figure out that it changed. > > > > The change is APM or ACPI initiated. Intel won't tell anyone anything > > useful but Microsoft have published some of the required > > intel confidential > > information which helps a bit > > APM is a lost cause, but the correct solution for ACPI systems is to use the > PM timer. This totally obviates the need to really care about the CPU's > effective frequency at all. Even if you knew all the details of SpeedStep > (and I've seen the same MS doc you have Alan and was surprised at its > detail) you'd still be hosed if the CPU throttles...you'd be hosed in a > *good* way because at least any delays would be longer (not shorter) than > expected but your times would be off nonetheless. And if it is thermal-throttledduring bogomips calibration...? [Well possible, acpi is not active that early] -- Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt, details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.