linux-kernel - Re: Linux 2.6.29-rc6

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Date:	Thu, 26 Feb 2009 23:04:03 +0100
From:	Jesper Krogh <jesper@...gh.cc>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	john stultz <johnstul@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29-rc6

Thomas Gleixner wrote:
> On Thu, 26 Feb 2009, 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?
>>
>> >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. 
> 
> But why would it do that on 29-rc6 and not on 2.6.28.8 ? I'm not aware
> of changes which might cause that.

My comparison is 2.6.26.8 not 2.6.28.8 .. so fairly old.

It is a small cluster, so I'm slipping some test-kernels in when the
cluster is idle.

-- 
Jesper
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