Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932612AbWALSIo (ORCPT ); Thu, 12 Jan 2006 13:08:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932530AbWALSIo (ORCPT ); Thu, 12 Jan 2006 13:08:44 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:18121 "EHLO e36.co.us.ibm.com") by vger.kernel.org with ESMTP id S932612AbWALSIn (ORCPT ); Thu, 12 Jan 2006 13:08:43 -0500 Subject: Re: Back to the Future ? or some thing sinister ? From: john stultz To: Ram Gupta Cc: Nathan Lynch , Chaitanya Hazarey , linux-kernel@vger.kernel.org In-Reply-To: <728201270601120633i1c9072fp3329d05b49de790f@mail.gmail.com> References: <20060109040322.GA2683@localhost.localdomain> <1137016986.2890.57.camel@cog.beaverton.ibm.com> <728201270601120633i1c9072fp3329d05b49de790f@mail.gmail.com> Content-Type: text/plain Date: Thu, 12 Jan 2006 10:08:17 -0800 Message-Id: <1137089297.2890.118.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1460 Lines: 33 On Thu, 2006-01-12 at 08:33 -0600, Ram Gupta wrote: > On 1/11/06, john stultz wrote: > > On Sun, 2006-01-08 at 22:03 -0600, Nathan Lynch wrote: > > > Chaitanya Hazarey wrote: > > > > > > > > We have got a machine, lets say X , make is IBM and the CPU is Intel > > > > Pentium 4 2.60 GHz. Its running a 2.6.13.1 Kernel and previously, > > > > 2.6.27-4 Kernel the distribution is Debian Sagre. > > It may be BIOS related. But I feel it might be an overflow related > issue. If the variable is signed int then there will be a transition > from 0x7fffffff ns to 0x80000000 ns which is basically from +2 sec to > -2 sec which will result in 4 sec loss. I'm pretty sure this is the BIOS issue. If your hesitant about updating the BIOS, try booting w/ noapic, and see if that works around the issue. The 4 second loss is the tv_nsec portion of the xtime timespec wrapping. Since time is not accumulated (timer_interrupt isn't being called at the normal HZ frequency), the TSC offset grows and grows (and finally will wrap repeating the processes), causing the xtime.tv_nsec to wrap. Thus you are correct that the symptom is overflow related, but the cause is most likely the BIOS. thanks -john - 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/