Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161156AbVIPKaH (ORCPT ); Fri, 16 Sep 2005 06:30:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161157AbVIPKaH (ORCPT ); Fri, 16 Sep 2005 06:30:07 -0400 Received: from dtp.xs4all.nl ([80.126.206.180]:29761 "HELO abra2.bitwizard.nl") by vger.kernel.org with SMTP id S1161156AbVIPKaF (ORCPT ); Fri, 16 Sep 2005 06:30:05 -0400 Date: Fri, 16 Sep 2005 12:30:02 +0200 From: Rogier Wolff To: Jesper Juhl Cc: "Randy.Dunlap" , linux-kernel@vger.kernel.org Subject: Re: early printk timings way off Message-ID: <20050916103002.GA19839@bitwizard.nl> References: <200509152342.24922.jesper.juhl@gmail.com> <9a87484905091515072c7dd4a8@mail.gmail.com> <9a87484905091515495f435db7@mail.gmail.com> <9a874849050915160027db1fe9@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a874849050915160027db1fe9@mail.gmail.com> Organization: BitWizard.nl User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1714 Lines: 37 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. Roger. -- ** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 ** *-- BitWizard writes Linux device drivers for any device you may have! --* Q: It doesn't work. A: Look buddy, doesn't work is an ambiguous statement. Does it sit on the couch all day? Is it unemployed? Please be specific! Define 'it' and what it isn't doing. --------- Adapted from lxrbot FAQ - 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/