Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030239AbWHQWct (ORCPT ); Thu, 17 Aug 2006 18:32:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030276AbWHQWct (ORCPT ); Thu, 17 Aug 2006 18:32:49 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:18142 "EHLO e2.ny.us.ibm.com") by vger.kernel.org with ESMTP id S1030239AbWHQWcs (ORCPT ); Thu, 17 Aug 2006 18:32:48 -0400 Subject: Re: Linux time code From: john stultz To: Jesse Barnes Cc: Roman Zippel , Ulrich Windl , linux-kernel@vger.kernel.org, Udo van den Heuvel In-Reply-To: <200608171512.00417.jbarnes@virtuousgeek.org> References: <44E32B23.16949.BBB1EC4@Ulrich.Windl.rkdvmks1.ngate.uni-regensburg.de> <1155851917.31755.125.camel@cog.beaverton.ibm.com> <200608171512.00417.jbarnes@virtuousgeek.org> Content-Type: text/plain Date: Thu, 17 Aug 2006 15:32:44 -0700 Message-Id: <1155853964.31755.131.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-4.fc4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1637 Lines: 39 On Thu, 2006-08-17 at 15:11 -0700, Jesse Barnes wrote: > On Thursday, August 17, 2006 2:58 pm, john stultz wrote: > > On Thu, 2006-08-17 at 13:43 +0200, Roman Zippel wrote: > > > On Wed, 16 Aug 2006, john stultz wrote: > > > > > For example there is a POSIX-like sys_clock_gettime() intended > > > > > to server the end-user directly, but there's no counterpart > > > > > do_clock_gettime() to server any in-kernel needs. > > > > > > > > Hmmm.. ktime_get(), ktime_get_ts() and ktime_get_real(), provide > > > > this info. Is there something missing here? > > > > > > What is missing is the abiltity to map a clock to a posix clock, so > > > that you would have CLOCK_REALTIME/CLOCK_MONOTONIC as NTP controlled > > > clocks and other CLOCK_* as the raw clock. > > > > Is there a use case for this (wanting non-NTP corrected time on a > > system running NTPd) you have in mind? > > Isn't this what CLOCK_MONOTONIC[_HR] is for? It's not supposed to jump > around at all, so the basic usage model is to use this source for > timestamping purposes... Well, CLOCK_MONOTONIC is not affected by calls to settimeofday() so it will never go backward, however it does get frequency correction if provided by NTP (thus a second will be a correct second and you won't accumulate error). Also the _HR clocks have always been out of tree, so there isn't the binary compatibility worry. 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/