From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261875AbUJNMIk (ORCPT ); Thu, 14 Oct 2004 08:08:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263743AbUJNMIk (ORCPT ); Thu, 14 Oct 2004 08:08:40 -0400 Received: from mx2.magma.ca ([206.191.0.250]:28359 "EHLO mx2.magma.ca") by vger.kernel.org with ESMTP id S261875AbUJNMIi (ORCPT ); Thu, 14 Oct 2004 08:08:38 -0400 Subject: Re: Clock inaccuracy seen on NVIDIA nForce2 systems From: Jesse Stockall To: linux@horizon.com Cc: linux-kernel@vger.kernel.org, ACurrid@nvidia.com In-Reply-To: <20041014012754.25198.qmail@science.horizon.com> References: <20041014012754.25198.qmail@science.horizon.com> Content-Type: text/plain Message-Id: <1097755757.5114.7.camel@homer.blizzard.org> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 Date: Thu, 14 Oct 2004 08:09:17 -0400 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2004-10-13 at 21:27, linux@horizon.com wrote: > > The system is running 2.6.9-rc4 and has been up for 2 days. I'm showing > > an offset of -32 seconds and growing. > > That's -185 ppm (parts per million) error, or -0.0185%. > > Typical cheap quartz crystals are +/- 100 ppm, but there are some cheaper > than that, and ceramic resonators like > http://www.ecsxtal.com/cerares.htm > > I know Dave Mills learned from experience that the original +/-100 ppm > specs in NTP weren't wide enough and he had to change it to cope with > +/-500 ppm error in some clocks. > > It *could* just be your motherboard's clock source. possible but.... a) When I boot without 'acpi_skip_timer_override' and I fall back to using ExtINT for the timer there is no drift. b) I rebooted and set FSB spread spectrum to 1.0 and let the machine run over night. In 10 hours of uptime I'm off -45 seconds and growing. This is -0.125%. So clearly having spread spectrum enabled does affect the clock. Thanks Jesse -- Jesse Stockall