linux-kernel - Re: Linux 2.6.29-rc6

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Date:	Fri, 27 Feb 2009 07:30:39 +0100
From:	Jesper Krogh <jesper@...gh.cc>
To:	john stultz <johnstul@...ibm.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Linux 2.6.29-rc6

john stultz wrote:
> On Thu, 2009-02-26 at 22:35 +0100, Jesper Krogh wrote:
>> john stultz wrote:
>>> On Thu, Feb 26, 2009 at 12:43 PM, Jesper Krogh <jesper@...gh.cc> wrote:
>>>> Linus Torvalds wrote:
>>>>> On Thu, 26 Feb 2009, Jesper Krogh wrote:
>>>>>> 2.6.26.8 doesnt have this problem.
>>>>>>
>>>>>> The "current_clocsource" is the same on both systems.
>>>>>>
>>>>>> $ cat /sys/devices/system/clocksource/clocksource0/current_clocksource
>>>>>> tsc
>>>>> What does the frequency calibrate to? It should be in the dmesg. Does it
>>>>> differ by a big amount?
>>>> Non-working:
>>>> $ dmesg | grep -i freq
>>>> [    0.004007] Calibrating delay loop (skipped), value calculated using
>>>> timer frequency.. 4620.05 BogoMIPS (lpj=9240104)
>>>>
>>>> 2.6.26.8 doesn't have that information.
>>> I'm surprised the clocksource watchdog isn't catching it.
>>>
>>> What's the output from:
>>> cat /sys/devices/system/clocksource/clocksource0/available_clocksource
>> $ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
>> tsc acpi_pm jiffies
> 
> Hmm. Does booting w/ "clocksourc=acpi_pm" also show the severe (~550ppm,
> which NTP can't handle) drift?

I booted another server (identical hardware) with the same kernel and
the above clocksource line, it has run over night (8 hours) with full
load and ntp has not complained about anything on that server.

>>>From the dmesg, I don't see any major calibration difference right off. 
> 
> So I'd suspect something like TSC halting in idle could be causing
> problems, but the watchdog should catch that as well. My only guess at
> this point is that the ACPI PM is halting in idle along with the TSC. 
> 
> And you said this only happens under load? 

I cant say that, but I've only observed it under load.

-- 
Jesper
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