Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752667Ab0HWIqI (ORCPT ); Mon, 23 Aug 2010 04:46:08 -0400 Received: from mail-vw0-f46.google.com ([209.85.212.46]:43497 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751641Ab0HWIqE convert rfc822-to-8bit (ORCPT ); Mon, 23 Aug 2010 04:46:04 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=Rw0XRmmApL8vTqP+soP05Wd2nEVhYCQmbSurbdTGd3Sd6RFnkQBvd6v7nxHd85mhdO 2eOS37zpABTLecBLSv4X4YD4RG08vre15PGuUV3nLJ3zcSRkgxq+N3wq5V5yTbDtgrPV hdie8Ahq1sYJTMRlzdxuu9602wL/cjY7M63QU= MIME-Version: 1.0 In-Reply-To: References: Date: Mon, 23 Aug 2010 10:46:03 +0200 X-Google-Sender-Auth: 1ZKkxICXbCPKNh7nbJo0JCiUW7I Message-ID: Subject: Re: System time drifts when processor idle. From: jean-philippe francois To: Lin Ming Cc: "H. Peter Anvin" , linux-acpi@vger.kernel.org, LKML Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2823 Lines: 74 2010/8/21 Lin Ming : > On Fri, Aug 20, 2010 at 8:55 AM, jean-philippe francois > wrote: >> Hi, >> >> Please correct me if I am sending this to the wrong list. > > LKML is better for this issue. Added. > Thank you. I have been looking at the ML archives, and it seems there has been issue related to timekeeping lately. So I tested my script with a decently recent kernel : 2.6.36-rc1. The timekeeping bug described below still exists. >> >> I would like to debug the following issue, which I suspect is related >> to cpu losing track of time when going idle. >> >> When I run the following script : >> >> #!/bin/bash >> # set hwclock to system clock to start >> # the log file with the same time >> hwclock -w >> #start with a fresh logfile >> touch clocktest.log >> echo START > clocktest.log >> while [[ true ]] >> do >> ? ?systime=$(date) >> ? ?hwtime=$(hwclock -r) >> ? ?echo "$systime | $hwtime" >> clocktest.log >> ? ?sleep 20 >> done >> >> Expected output : >> On each line, the system time (left) and hardware time (right) >> should be roughly the same. Time delta between each line should be >> around 20 seconds >> >> Observed output : >> This is an edited version of the real logfile ?so that it fits on one >> line. the date was removed. >> START >> 15:09:43 (UTC+0200) | ?15:09:44 CEST -0.500555 secondes >> 15:10:04 (UTC+0200) | ?15:10:05 CEST -1.001562 secondes >> 15:10:25 (UTC+0200) | ?15:10:26 CEST -0.985944 secondes >> 15:10:46 (UTC+0200) | ?15:15:46 CEST -0.032792 secondes <-- 5 minute lag ! >> 15:11:06 (UTC+0200) | ?15:16:07 CEST -0.985926 secondes >> 15:11:27 (UTC+0200) | ?15:16:28 CEST -1.001539 secondes >> 15:11:48 (UTC+0200) | ?15:16:49 CEST -0.985969 secondes >> 15:12:09 (UTC+0200) | ?15:17:10 CEST -0.985977 secondes >> 15:12:30 (UTC+0200) | ?15:17:31 CEST -1.001544 secondes >> 15:12:51 (UTC+0200) | ?15:17:52 CEST -0.985920 secondes >> 15:13:12 (UTC+0200) | ?15:18:13 CEST -0.985939 secondes >> 15:13:33 (UTC+0200) | ?15:18:34 CEST -1.001581 secondes >> 15:13:54 (UTC+0200) | ?15:18:55 CEST -0.985917 secondes >> 15:14:15 (UTC+0200) | ?15:29:15 CEST -0.079685 secondes <-- add >> another 10 minute >> 15:14:35 (UTC+0200) | ?15:29:36 CEST -1.001568 secondes >> 15:14:56 (UTC+0200) | ?15:29:57 CEST -0.985952 secondes >> >> As you can see, after 20 minutes without touching the computer, the >> system time is late by 15 minutes. >> This was tested on ubuntu 10.04 with a 2.6.32 ?"vanilla" kernel where >> "vanilla" means ubuntu packaged >> upstream kernel ?closest to the distribution shipped kernel. >> -- 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/