From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758935AbZEMJv3 (ORCPT ); Wed, 13 May 2009 05:51:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755248AbZEMJvT (ORCPT ); Wed, 13 May 2009 05:51:19 -0400 Received: from av-gw1.cc.tut.fi ([130.230.130.110]:57184 "EHLO av-gw1.cc.tut.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753256AbZEMJvS (ORCPT ); Wed, 13 May 2009 05:51:18 -0400 X-AuditID: 82e6826e-a44c3bb0000009be-7c-4a0a91972bce Date: Wed, 13 May 2009 12:23:35 +0300 From: Petri Kaukasoina To: Ulrich Windl Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, Clark Williams , zippel@linux-m68k.org, Ingo Molnar Subject: Re: [PATCH] tsc_khz= boot option to avoid TSC calibration variance Message-ID: <20090513092335.GA22832@elektroni.phys.tut.fi> Mail-Followup-To: Ulrich Windl , Thomas Gleixner , linux-kernel@vger.kernel.org, Clark Williams , zippel@linux-m68k.org, Ingo Molnar References: <4A0A9A23.24720.54D53C4@Ulrich.Windl.rkdvmks1.ngate.uni-regensburg.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A0A9A23.24720.54D53C4@Ulrich.Windl.rkdvmks1.ngate.uni-regensburg.de> User-Agent: Mutt/1.4.2.3i X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 13, 2009 at 09:59:59AM +0200, Ulrich Windl wrote: > On 13 May 2009 at 0:42, Thomas Gleixner wrote: > > > Honestly all this is just the futile attempt to fix the flaws of NTP > > via (super)user interaction. > > This has nothing to do with flaws in NTP (AFAIK). Correct. When ntp is NOT RUNNING at all, if the TSC calibration gives a MHz value differing e.g. 100 ppm from the previous value, the clock will run at a different speed, 100 ppm making a difference of 17 seconds a day. On the other hand, if ntp is running, it will eventually compensate the offset. But it takes quite a long time to settle, IMO too long for a quality time server. The real changes in the clock frequency between bootups are in the order of 1 ppm, but the TSC calibration can be even 100 ppm off randomly. -Petri