Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161095AbVIPN4I (ORCPT ); Fri, 16 Sep 2005 09:56:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161096AbVIPN4I (ORCPT ); Fri, 16 Sep 2005 09:56:08 -0400 Received: from zproxy.gmail.com ([64.233.162.196]:37160 "EHLO zproxy.gmail.com") by vger.kernel.org with ESMTP id S1161095AbVIPN4H convert rfc822-to-8bit (ORCPT ); Fri, 16 Sep 2005 09:56:07 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:reply-to:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=pPSlTk3dx8ZQnNiNR81JAI6Oz3o6ImrXHgRCemizHVbpnzt2V154nY2rgLRz7npBEBsiShYO25wcEHeEzFG2rRcQ4gPjMhB+WB1POURwXS41t4VzJfEtYZ8hJYuzhs1GSI6DXbD2WI6Td0s+Iek7WC7XnX8Hb+NhFBVOiZ8hV6k= Message-ID: <9a874849050916065511a6f973@mail.gmail.com> Date: Fri, 16 Sep 2005 15:55:55 +0200 From: Jesper Juhl Reply-To: jesper.juhl@gmail.com To: Rogier Wolff Subject: Re: early printk timings way off Cc: "Randy.Dunlap" , linux-kernel@vger.kernel.org In-Reply-To: <20050916103002.GA19839@bitwizard.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Content-Disposition: inline References: <200509152342.24922.jesper.juhl@gmail.com> <9a87484905091515072c7dd4a8@mail.gmail.com> <9a87484905091515495f435db7@mail.gmail.com> <9a874849050915160027db1fe9@mail.gmail.com> <20050916103002.GA19839@bitwizard.nl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1651 Lines: 36 On 9/16/05, Rogier Wolff wrote: > On Fri, Sep 16, 2005 at 01:00:45AM +0200, Jesper Juhl wrote: > > > > I'll just dig into it myself for now, but thank you, if I get really > > stuck I may ask him. > > The explanation: "jiffies starts at rollover minus a bit" seems to be > spot-on: If jiffies are 32bit, and counting at 1000 per second, the > 2^32 / 1000 works out. > > I expect the kernel to run without turning on (timer) interrupts for a > while during boot: It is still initializing things like memory and the > processor. Without those, interrupts won't work. This means that the > timer interrupt will not count in real-time. > > A "jump" of 27 seconds seems unlikely, except if somehow the > interrupts are somehow accounted. It could very well be that the > kernel nowadays has a mechanism of measuring the fact that it missed a > timer interrupt and corrects for that. This would mean that around the > "jump", the kernel suddenly realized it missed around 27000 interrupts > and added 27000 to "jiffies".... > > I'd say: Would be nice to get the timings right, but not worth the > trouble: There are good technical reasons for the observed facts. > Thank you for that explanation Rogier. -- Jesper Juhl Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - 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/