Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756951AbZFBAVG (ORCPT ); Mon, 1 Jun 2009 20:21:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754849AbZFBAU7 (ORCPT ); Mon, 1 Jun 2009 20:20:59 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:53230 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754320AbZFBAU6 (ORCPT ); Mon, 1 Jun 2009 20:20:58 -0400 Date: Tue, 2 Jun 2009 02:20:39 +0200 From: Ingo Molnar To: Rik van Riel Cc: John Stultz , mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org, Miroslav Lichvar Subject: Re: [tip:timers/ntp] ntp: adjust SHIFT_PLL to improve NTP convergence Message-ID: <20090602002039.GA16410@elte.hu> References: <200905051956.n45JuVo9025575@imap1.linux-foundation.org> <1243542817.29511.523.camel@jstultz-laptop> <20090601232223.GH749@elte.hu> <1243900716.11263.42.camel@jstultz-laptop> <4A246D0B.40204@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A246D0B.40204@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1573 Lines: 38 * Rik van Riel wrote: > John Stultz wrote: >> On Tue, 2009-06-02 at 01:22 +0200, Ingo Molnar wrote: > >>> I might be missing something here - but Linux converging faster >>> seems like a genuinely good thing. What non-Linux problem could >>> there be? Linux's convergence is really Linux's private issue. >> >> Yea. It does seem that way. Miroslav can likely expand on the >> issue to help clarify, but as I understand it, the example is if >> you have a number of systems that are peers in an NTP network. >> All of them are using the same userland NTP daemon. However, if >> the rate of change that corrections are applied is different in >> half of them, you will have problems getting all the systems to >> converge together. > > Would this not be true already, because the convergence of Linux > system suddenly became a lot slower in 2.6.19? > > Damned if we do, damned if we don't - except the new behaviour > introduced by your patches is nicer. Not just that - but there's calibration noise during bootup that can cause randomly distributed recalibrations as well. So other hosts in a mixed environment will see inconsistencies anyway, after every bootup. NTP is all about being able to be resilient against time noise and being able to sync up to a common time base ASAP. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/