From owner-freebsd-current@FreeBSD.ORG Tue Jan 3 06:18:10 2006 Return-Path: X-Original-To: current@freebsd.org Delivered-To: freebsd-current@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id B364616A41F for ; Tue, 3 Jan 2006 06:18:10 +0000 (GMT) (envelope-from PeterJeremy@optushome.com.au) Received: from mail11.syd.optusnet.com.au (mail11.syd.optusnet.com.au [211.29.132.192]) by mx1.FreeBSD.org (Postfix) with ESMTP id ED25E43D58 for ; Tue, 3 Jan 2006 06:18:09 +0000 (GMT) (envelope-from PeterJeremy@optushome.com.au) Received: from cirb503493.alcatel.com.au (c220-239-19-236.belrs4.nsw.optusnet.com.au [220.239.19.236]) by mail11.syd.optusnet.com.au (8.12.11/8.12.11) with ESMTP id k036HqCw003702 (version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO); Tue, 3 Jan 2006 17:17:53 +1100 Received: from cirb503493.alcatel.com.au (localhost.alcatel.com.au [127.0.0.1]) by cirb503493.alcatel.com.au (8.12.10/8.12.10) with ESMTP id k036HqHh046693; Tue, 3 Jan 2006 17:17:52 +1100 (EST) (envelope-from pjeremy@cirb503493.alcatel.com.au) Received: (from pjeremy@localhost) by cirb503493.alcatel.com.au (8.12.10/8.12.9/Submit) id k036HqMx046692; Tue, 3 Jan 2006 17:17:52 +1100 (EST) (envelope-from pjeremy) Date: Tue, 3 Jan 2006 17:17:52 +1100 From: Peter Jeremy To: "M. Warner Losh" Message-ID: <20060103061752.GE42228@cirb503493.alcatel.com.au> References: <73774.1136109554@critter.freebsd.dk> <20060102.221046.75255380.imp@bsdimp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060102.221046.75255380.imp@bsdimp.com> User-Agent: Mutt/1.4.2.1i X-PGP-Key: http://members.optusnet.com.au/peterjeremy/pubkey.asc Cc: current@freebsd.org Subject: Re: FreeBSD handles leapsecond correctly X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Jan 2006 06:18:10 -0000 On Mon, 2006-Jan-02 22:10:46 -0700, M. Warner Losh wrote: >The biggest problem with compiling leap seconds into this is that you >can only be sure that leap seconds are right for at most 6 months. >Sure, you can make statistical statements about how likely a leap >second is or isn't going to be, but this non-determinism is a big >problem. There's no way you can deploy a system and have a sane leap >second table without a connection to the outside world... The Islamic calendar is based on lunar _sightings_: If it's cloudy, the calendar shifts a day. This wreaks even more havoc than the odd leap-second and many Islamic countries have therefore switched to using almanac based dates. Actually, I'd suggest that you can't build a system that keeps any sort of accurate time without a connection to the outside world or a quite substantial budget. If you assume a leap second every 5 years then the difference between UTC and TAI is about 6e-9 - being able to tell the difference requires an atomic clock - which isn't common in embedded systems. >Leap seconds are hard and I hate them. Which of the competing alternatives would you prefer? -- Peter Jeremy