Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932134AbXBNG7L (ORCPT ); Wed, 14 Feb 2007 01:59:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751508AbXBNG7K (ORCPT ); Wed, 14 Feb 2007 01:59:10 -0500 Received: from styx.suse.cz ([82.119.242.94]:49560 "EHLO mail.suse.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751504AbXBNG7J (ORCPT ); Wed, 14 Feb 2007 01:59:09 -0500 Date: Wed, 14 Feb 2007 07:59:05 +0100 From: Vojtech Pavlik To: Andrea Arcangeli Cc: Andi Kleen , Christoph Lameter , Arjan van de Ven , Jiri Bohac , linux-kernel@vger.kernel.org, ssouhlal@freebsd.org, tglx@linutronix.de, johnstul@us.ibm.com, zippel@linux-m68k.org Subject: Re: [patch 4/9] Remove the TSC synchronization on SMP machines Message-ID: <20070214065905.GA10887@suse.cz> References: <20070201095952.589234000@jet.suse.cz> <1171348808.12771.19.camel@laptopd505.fenrus.org> <200702131820.15180.ak@suse.de> <20070213221848.GF9189@suse.cz> <20070213223833.GB7615@v2.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070213223833.GB7615@v2.random> X-Bounce-Cookie: It's a lemon tree, dear Watson! User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1250 Lines: 30 On Tue, Feb 13, 2007 at 11:38:33PM +0100, Andrea Arcangeli wrote: > Hi, > > On Tue, Feb 13, 2007 at 11:18:48PM +0100, Vojtech Pavlik wrote: > > It's not inherent to ntpd's design, but the current (which may have been > > fixed since I looked last) implementation of the NTP PLL in the kernel. > > > > The interaction with ntpd can be fixed and I've done it in the past > > once, although the fix wasn't all that nice. > > Yep, it can slowly move towards the correct time, but ntpdate (or more > generally settimeofday) remains a fundamental issue (and I prefer time > skews to be fixed ASAP, not slowly). Skipping forward is trivial. For going backward, you can stop time (or make it go forward very slowly). Still the output will be strictly monotonic (but not more than that). For small changes you simply change your estimate of the base clock frequency to be different from what the specs say. Tuning that in a PLL will get you to sync with true atomic GMT. -- Vojtech Pavlik Director SuSE Labs - 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/