linux-kernel - Re: Linux 2.6.29-rc6

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Message-ID: <49AA92E6.6020103@krogh.cc>
Date:	Sun, 01 Mar 2009 14:51:34 +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?
> 
>>>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? 

That wasn't true.. I got some real sunday testing done today. A fresh 
2.6.28.7 has the same problem with a load of 0.00 0.00 0.00

2.6.27.19 doesn't have problems keeping time.

-- 
Jesper
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