From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763300AbYDOBZ2 (ORCPT ); Mon, 14 Apr 2008 21:25:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757469AbYDOBZT (ORCPT ); Mon, 14 Apr 2008 21:25:19 -0400 Received: from terminus.zytor.com ([198.137.202.10]:42277 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757393AbYDOBZS (ORCPT ); Mon, 14 Apr 2008 21:25:18 -0400 Message-ID: <480403DE.4070901@zytor.com> Date: Mon, 14 Apr 2008 18:24:46 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: Krzysztof Halasa CC: Lennart Sorensen , Marc Perkel , Chris Snook , linux-kernel@vger.kernel.org Subject: Re: AMD Quad Core clock problem? References: <47FFD3F3.50107@redhat.com> <821384.64293.qm@web52504.mail.re2.yahoo.com> <20080411213843.GH2160@csclub.uwaterloo.ca> <4802608A.3040901@zytor.com> <20080414151222.GF7385@csclub.uwaterloo.ca> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Krzysztof Halasa wrote: > lsorense@csclub.uwaterloo.ca (Lennart Sorensen) writes: > >> True, but usually they give you an option to turn it off in the BIOS to >> make the system actually work with things like NTP. >> >> Maybe I should have said "Any system with spread spectrum enabled". > > I haven't investigated those spread spectrums at all but sometimes > there are options: "center" (the frequency is centered around the > nominal value, I guess) and "below" (or something like that). If done > correctly, "center" shouldn't have visible effect on NTP, should it? It shouldn't really matter, since "below" produces a similar spectrum at a slightly lower frequency. The main issue is how slow the frequency slew really is; typically the slew should well average out to zero over the timescale that NTP cares about. > The other important question is "what frequency has spread spectrum > enabled"? CPU (= TSC), HPET, RAM, something else? In PCs, the TSC and RAM will be affected; the HPET, PMTMR and PIT are fed from the 14.31818 MHz timekeeping crystal which is generally *not* spread. -hpa