From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764722AbYEGTAZ (ORCPT ); Wed, 7 May 2008 15:00:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932687AbYEGS7m (ORCPT ); Wed, 7 May 2008 14:59:42 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:37590 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1764240AbYEGS7k (ORCPT ); Wed, 7 May 2008 14:59:40 -0400 Subject: Re: 2.6.25.2 - Jiffies/Time jumping back and forth (Regereesion from 2.6.24) From: John Stultz To: Martin Knoblauch Cc: linux-kernel@vger.kernel.org, Chris McDermott In-Reply-To: <572961.18046.qm@web32607.mail.mud.yahoo.com> References: <572961.18046.qm@web32607.mail.mud.yahoo.com> Content-Type: text/plain Date: Wed, 07 May 2008 11:59:38 -0700 Message-Id: <1210186778.16386.5.camel@jstultz-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.22.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2008-05-07 at 11:14 -0700, Martin Knoblauch wrote: > > The printk timestamps may jump around a bit at bootup, especially if > > you have unsynced TSCs, so that is a known issue. However its not > > known to have any actual negative effect other then maybe causing the > > dmesg log to be a bit confusing. > > > > the problem, is not just at bootup and the jumping. During the > *complete* lifetime of the kernel I see: > > a) the dmesg timestamps jumping back and forth > b) the values are much to small and have absolutely no relation to > "seconds after bootup", as they have with 2.6.24 and before. > > But you are right, it might not be a jiffie problem, but a "dmesg > timestamp" thing. Hrmm.. So the issue persisting over the lifetime of the kernel is a new one by me. This may also have some effect in scheduling decisions (not necessarily causing a correctness issue, but a performance one). Also it may have some effect on thread cputime values. Please do open a bug and provide example dmesg output. I'll try to tag some folks who have access to the same system type. thanks -john