Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757104AbZAGEwc (ORCPT ); Tue, 6 Jan 2009 23:52:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752887AbZAGEwX (ORCPT ); Tue, 6 Jan 2009 23:52:23 -0500 Received: from yx-out-2324.google.com ([74.125.44.28]:47572 "EHLO yx-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751859AbZAGEwW (ORCPT ); Tue, 6 Jan 2009 23:52:22 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:reply-to:to:subject:cc:in-reply-to :mime-version:content-type:content-transfer-encoding :content-disposition:references; b=Bt5pc15grlK2JZsmsC8fffoldnE1anVviWhD5ypjeCXbGoFwrEG74thnqfc0rXp0ty OqWpQO1bCaSmtUEPanwTi6sD0zsXtk4vT9AN2TWMML30gwnval/rCARypp76vdgqt6TM oZGMTJPdtBxqdZ9SmkpU4oZpXuKXYZf3OaHq0= Message-ID: <3ae3aa420901062052h75fcab11n8ce45c41ac0e4cd2@mail.gmail.com> Date: Tue, 6 Jan 2009 22:52:20 -0600 From: "Linas Vepstas" Reply-To: linasvepstas@gmail.com To: mayer@ntp.isc.org Subject: Re: [ntpwg] Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009 Cc: david@lang.hm, "Robert Hancock" , "Ben Goodger" , "Kyle Moffett" , MentalMooMan , "David Newall" , linux-kernel@vger.kernel.org, ntpwg@lists.ntp.isc.org, "Travis Crump" , burdell@iruntheinter.net, "Nick Andrew" , "Jeffrey J. Kosowsky" In-Reply-To: <49642674.9080703@ntp.isc.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <495F0672.6020708@davidnewall.com> <4961432A.80509@davidnewall.com> <49614835.7000505@davidnewall.com> <3ae3aa420901042148o1c96985dube8e03085c997a07@mail.gmail.com> <20090105143335.GC18055@mail.local.tull.net> <3ae3aa420901050808r100e533fo5f88edfbb5f0747a@mail.gmail.com> <3ae3aa420901050942y56f0ecdei39c091a73e49c1fd@mail.gmail.com> <49642674.9080703@ntp.isc.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2870 Lines: 65 2009/1/6 Danny Mayer : Hi, > I don't know what this discussion is really about and why this was sent > to the working group in the middle of the discussion, but there is no > need for NTP to provide TAI information since NTP only uses UTC. Leap > Seconds are automatically signaled and incorporated when they become > due. If you don't have NTP running for some reason when a leap second is > signaled it doesn't matter since your server source will already have > incorporated the leap second so the NTP packet includes the timestamps > that include the leap second adjustment. > > Operating Systems use UTC and not TAI by universal agreement and the > ones that don't are extremely rare. > > Why don't you tell us what the real problem is instead of telling us > that you need TAI offset information? Currently, the Linux kernel keeps time in UTC. This means that it must take special actions to tick twice when a leap second comes by. Due to a (stupid) bug, some fraction of linux systems crashed; this includes everything from laptops to servers, to DVR's, to cell phones and cell phone towers. There's now a fix for this. However, during the discussion, the idea came out that maybe keeping UTC time in the kernel is just plain stupid. So there's this idea floating around that maybe the kernel should keep TAI time instead. The hope is that this will reduce the complexity in the kernel, and push it out to user space, "where it belongs" (to repeat a well-worn mantra). However, *if* we were to kick UTC out of the kernel, and push it to user-land, then, of course, there's a different problem: how does the kernel know what the correct TAI time is? As your reply makes abundantly clear, NTP is not a good source for TAI information. The comments which you labelled as "non-sense" were a mis-understanding of a discussion of a particular issue that would arise if the kernel were to keep TAI -- if it did, then user-space systems would need to have a reliable source for leap-seconds. Since NTP does not provide this, there was discussion about how that could be worked-around. This then lead to the comment that, "gee, wouldn't the right long-term solution be that NTP provide TAI info?" Clearly, it would be a lot of work to get the kernel to keep TAI instead of UTC, so this is not, at this time, a "serious proposal". But if it were possible, and all the various little issues that result were solvable, then it does seem like a better long-term solution. --linas p.s. the opinions above are not my own; I'm just summarizing the points made by the most vocal posters to this list. -- 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/