linux-kernel - Re: Fw: [BUG 2.6.21-rc7] acpi_pm clocksource loses time on x86-64

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Message-Id: <1178129409.6183.12.camel@localhost.localdomain>
Date:	Wed, 02 May 2007 11:10:09 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Mikael Pettersson <mikpe@...uu.se>
Cc:	Len Brown <len.brown@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...e.de>
Subject: Re: Fw: [BUG 2.6.21-rc7] acpi_pm clocksource loses time on x86-64

On Sun, 2007-04-29 at 17:24 +0200, Mikael Pettersson wrote:
> On Thu, 26 Apr 2007 15:42:44 -0700, john stultz wrote:
> >Another shot in the dark:
> >
> >I wonder if the ACPI PM counter is halting in idle. Does booting w/
> >idle=poll change the behavior? (Please do this while your laptop is
> >plugged in, as it will run the cpu at full speed all the time).
> 
> Bingo!

Awesome! Finally, some progress! Thanks again for putting up w/ all my
testing requests.

> I booted the x86-64 2.6.21 final kernel with idle=poll and let the
> laptop idle for an hour. The ondemand cpufreq governor did reduce
> the CPU's clock frequency, but that shouldn't have affected the
> chipset or the ACPI PM counter.
> 
> Anyway, after 60 minutes `date' and `hwclock' were still in perfect
> sync and matched actual time.
> 
> Any ideas why this halting in idle doesn't happen with the 32-bit kernel?

No clue. Time to ask Len. :)

Hey Len,
	So that slow acpi_pm on x86_64 seems to be connected w/ the idle loop.
I'm guessing the chipset halts the ACPI PM in lower C states. Do you
have any guesses as to what might differ between x86_64 and i386 ACPI
idle loops? Or might this be something different in what the BIOS
exports in x86_64 mode or i386 mode?

Any suggestions on how to dig through this?


Thomas: Heads up, the ACPI PM might be flakier then we thought.

thanks
-john



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