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

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Date:	Thu, 09 Sep 2010 10:42:05 -0700
From:	john stultz <johnstul@...ibm.com>
To:	jean-philippe francois <jp.francois@...ove.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.

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.

thanks
-john


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