linux-kernel - Re: System time drifts when processor idle.

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Message-ID: <AANLkTimCQnoY2FmRe4Gcf8vgxp4QanYXftRaD9gvrejy@mail.gmail.com>
Date:	Mon, 13 Sep 2010 15:04:36 +0200
From:	jean-philippe francois <jp.francois@...ove.com>
To:	john stultz <johnstul@...ibm.com>
Cc:	Lin Ming <lin@...g.vg>, venki@...gle.com,
	"H. Peter Anvin" <hpa@...or.com>, linux-acpi@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, jslaby@...e.cz
Subject: Re: System time drifts when processor idle.

2010/9/9 john stultz <johnstul@...ibm.com>:
> On Fri, 2010-09-03 at 14:23 +0200, jean-philippe francois wrote:
>> 2010/8/27 john stultz <johnstul@...ibm.com>:
>> > On Fri, 2010-08-27 at 16:12 +0200, jean-philippe francois wrote:
>> >> My Timekeeping bug is still present, here is an updated script and log.
>> >> I am willing to make test, but I don't know what kind of debugging
>> >> info is needed.
>> >>
>> >> cat /sys/devices/system/clocksource/clocksource0/available_clocksource
>> >> hpet acpi_pm
>> >> cat /sys/devices/system/clocksource/clocksource0/current_clocksource
>> >> hpet
>> >
>> > Huh. hpet was not what I would have expected.
>> >
>> >
>> > So first, two experiments:
>> >
>> > 1) Does booting with "clock=acpi_pm" cause the issue to disappear?
>> >
>>
>> Hi,
>>
>> The same bug happens with clock=acpi_pm.
>> My apologies for a previous mail where I said it was not hapenning with acpi_pm.
>>
>> With both clock, the timekeeping gap augments by amount of 5 minutes.
>
> Huh. So this still seems strange, but assuming we're still using the
> hpet for irqs, its possible the event somehow gets pushed back 5 minutes
> and we miss an timekeeping interval accumulation (with acpi_pm, the
> counter wraps ever 5 seconds or so, so we could miss many accumulation
> intervals and still be 5 minutes off if the tick timer was late).
>
> Again, seeing if the issue goes away with nohz=off would be helpful.
>

It  goes away witj nohz=off

Thank you for your interest.
Jean-Philippe François
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