From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756892Ab0EZTvQ (ORCPT ); Wed, 26 May 2010 15:51:16 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:59557 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756585Ab0EZTvO (ORCPT ); Wed, 26 May 2010 15:51:14 -0400 Subject: Re: [PATCH] x86: Export tsc related information in sysfs From: john stultz To: Brian Bloniarz Cc: "H. Peter Anvin" , Dan Magenheimer , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Andi Kleen , Arjan van de Ven , Venkatesh Pallipadi , chris.mason@oracle.com, linux-kernel@vger.kernel.org In-Reply-To: <4BFD6C2B.4070403@athenacr.com> References: <4BF58B59.7080901@athenacr.com> <1274727116.2954.5.camel@localhost.localdomain> <4BFADF9D.9050209@zytor.com 1274733566.2954.73.camel@localhost.localdomain> <3ec7f284-1507-47fb-b5a2-eea29f68c627@default> <4BFAFE17.8060105@zytor.com> <4BFB2902.50308@athenacr.com> <4BFC687A.9040304@athenacr.com> <1274834888.4678.66.camel@localhost.localdomain> <4BFC8C77.7020802@athenacr.com> <1274886299.1759.8.camel@work-vm> <4BFD4629.6040602@athenacr.com> <1274891109.1759.27.camel@work-vm> <4BFD6C2B.4070403@athenacr.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 26 May 2010 12:49:50 -0700 Message-ID: <1274903390.3383.17.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-05-26 at 14:44 -0400, Brian Bloniarz wrote: > On 05/26/2010 12:25 PM, john stultz wrote: > > Brian: is this something the NTPd folks actually want? Has anyone > > checked with them before we hand down the solution from high upon on > > lkml mountain? > > I haven't checked, it's been a while since I dealt with > this problem. The NTP maintainers definitely complain about the > quick TSC calibration code like it's a bug: > (e.g. http://www.mail-archive.com/questions@lists.ntp.org/msg02079.html). > Anyway I'll reach out before I spend any time investing in > a solution that they don't want (and you don't like :). > > > Personally I think NTPd should be a little more savvy about how far it > > trusts the drift file when it starts up. Since I believe its > > fast-startup mode can quickly estimate the drift well within 100ppm, > > which is about the maximum variance I've seen from the calibration code. > > The workaround we went with was to remove the drift file on > every reboot. But in our experience, even with iburst, converging takes > a long time. I don't have hard numbers since it's been a long time since > I investigated the problem, but we defined failure as >1ms offset syncing > to a server in our LAN, and a cold NTP boot takes 10-20 hours to get > there. Ok. If its been awhile, you may find recent kernels (2.6.31+) are much faster to converge due to adjustments made to the SHIFT_PLL constant. This was done explicitly to address issues similar to what you describe above. thanks -john