From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932121Ab0EXSY0 (ORCPT ); Mon, 24 May 2010 14:24:26 -0400 Received: from terminus.zytor.com ([198.137.202.10]:56970 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758266Ab0EXSYP (ORCPT ); Mon, 24 May 2010 14:24:15 -0400 Message-ID: <4BFAC34C.5020606@zytor.com> Date: Mon, 24 May 2010 11:19:56 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-2.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Dan Magenheimer CC: john stultz , Brian Bloniarz , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Andi Kleen , Arjan van de Ven , Venkatesh Pallipadi , chris.mason@oracle.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: Export tsc related information in sysfs References: <4BF58B59.7080901@athenacr.com AANLkTinJ36UBMsVvTEoPnmAVS6np9Ja6heEtKA93r7tp@mail.gmail.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/24/2010 11:13 AM, Dan Magenheimer wrote: > Just wondering: If one were to put an ultra-precise scope on > a processor, how far off would the calibrated value be? I'd > imagine the process of calibrating one unknown crystal against > a second crystal which has a known-but-not-highly-precise > frequency, though good enough for most purposes, is not particularly > accurate. In other words, maybe the stamped rate is more accurate > than the calibrated rate anyway? No. Not even close. A spread-spectrum clock is inaccurate by entire percentage points. A non-spread clock is typically ±50 ppm with typical consumer PC oscillators, ±1 ppm with non-crappy but still cheap oscillators (e.g. used in cell phones.) -hpa