From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262395AbVGMTjK (ORCPT ); Wed, 13 Jul 2005 15:39:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262422AbVGMTg0 (ORCPT ); Wed, 13 Jul 2005 15:36:26 -0400 Received: from kanga.kvack.org ([66.96.29.28]:41160 "EHLO kanga.kvack.org") by vger.kernel.org with ESMTP id S262378AbVGMTej (ORCPT ); Wed, 13 Jul 2005 15:34:39 -0400 Date: Wed, 13 Jul 2005 15:35:40 -0400 From: Benjamin LaHaise To: Linus Torvalds Cc: Vojtech Pavlik , David Lang , Bill Davidsen , Con Kolivas , Linux Kernel Mailing List , "Martin J. Bligh" , Lee Revell , Diego Calleja , azarah@nosferatu.za.org, akpm@osdl.org, cw@f00f.org, christoph@lameter.com Subject: Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt Message-ID: <20050713193540.GD26172@kvack.org> References: <200506231828.j5NISlCe020350@hera.kernel.org> <20050712121008.GA7804@ucw.cz> <200507122239.03559.kernel@kolivas.org> <200507122253.03212.kernel@kolivas.org> <42D3E852.5060704@mvista.com> <20050712162740.GA8938@ucw.cz> <42D540C2.9060201@tmr.com> <20050713184227.GB2072@ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2005 at 12:10:48PM -0700, Linus Torvalds wrote: > Long-term time drift is a known issue, and is unavoidable since you don't > even know the exact frequency of the crystal, since that is not only not > that exact in the first place, it depends on temperature etc. So long-term > time drift is something that we inevitably have to use things like NTP to > handle, if you want an exact clock. diz gave #kernel a good diatribe a few weeks ago about the headaches associated with using the PIT as a clock source, with one of the more interesting tidbits being that chipsets will pull the frequency higher and lower at times in order to implement spread spectrum to comply with RF emissions. The RTC doesn't suffer from this, but it only provides HZ values which are powers of two. How bad would 256 Hz be? -ben -- "Time is what keeps everything from happening all at once." -- John Wheeler