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Date: Mon, 23 Aug 2010 15:17:39 -0700 From: john stultz <johnstul@...ibm.com> To: jean-philippe francois <jp.francois@...ove.com> Cc: Lin Ming <lin@...g.vg>, "H. Peter Anvin" <hpa@...or.com>, linux-acpi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: System time drifts when processor idle. On Mon, Aug 23, 2010 at 1:46 AM, jean-philippe francois <jp.francois@...ove.com> wrote: > 2010/8/21 Lin Ming <lin@...g.vg>: >> On Fri, Aug 20, 2010 at 8:55 AM, jean-philippe francois >> <jp.francois@...ove.com> 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. Could you provide the output of: cat /sys/devices/system/clocksource/clocksource0/available_clocksource cat /sys/devices/system/clocksource/clocksource0/current_clocksource I assume you're using the TSC, and hitting the halt-in-c3 issue, but I'm curious why the clocksource watchdog isn't catching this and dropping you back to a more stable clocksource. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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