Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758802AbZFWVmL (ORCPT ); Tue, 23 Jun 2009 17:42:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752122AbZFWVl7 (ORCPT ); Tue, 23 Jun 2009 17:41:59 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:48331 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751180AbZFWVl6 (ORCPT ); Tue, 23 Jun 2009 17:41:58 -0400 Subject: Re: [GIT pull] ntp updates for 2.6.31 From: john stultz To: Ingo Molnar Cc: Miroslav Lichvar , Thomas Gleixner , Linus Torvalds , Andrew Morton , LKML , Martin Schwidefsky In-Reply-To: <20090623133625.GA3026@elte.hu> References: <1f1b08da0906151316s7d25f8ceraa1bc967a8abe172@mail.gmail.com> <1f1b08da0906151641u4cd964e6vf1a61afe50cc1d90@mail.gmail.com> <20090616090647.GD13771@elte.hu> <20090616125248.GA23541@localhost> <1245253102.6067.94.camel@jstultz-laptop> <20090617172325.GA32332@localhost> <20090617172601.GA3493@elte.hu> <20090618121320.GA13025@localhost> <20090623095745.GC30634@elte.hu> <20090623131628.GA11827@localhost> <20090623133625.GA3026@elte.hu> Content-Type: text/plain Date: Tue, 23 Jun 2009 14:41:56 -0700 Message-Id: <1245793316.3305.5.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1243 Lines: 30 On Tue, 2009-06-23 at 15:36 +0200, Ingo Molnar wrote: > The PPS patches i've seen just export IRQ timestamps to user-space. > > That is not very robust in my opinion when it comes to do time > approximations - to get quick, low-latency action and precise > measurements it's best to keep the critical path as short as > possible, and within a single source code repository: i.e. within > the kernel. > > There's little policy really, other than setting some general > parameters. NTPd can still provide the raw _network time_ > timestamps, as that is probably best fetched by user-space and fed > to the kernel. At some point that stops being NTP. NTP has quite a bit of userland policy for filtering and managing a number of different network clocks (other ntp servers, PPS sources, etc). >From what you're describing (direct offset from a hardware time device used to steer the clock directly in kernel), you might want to look at the STP code in s390 (stp_sync_clock). thanks -john -- 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/