linux-kernel - Re: CPU hyperthreading turned on after soft power-cycle

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Date:	Mon, 21 Nov 2011 14:27:21 +0100
From:	Jiri Polach <jiri.polach@...nam.cz>
To:	John Stultz <john.stultz@...aro.org>
CC:	Jiri Polach <clarinet@...as.cz>, 647095@...s.debian.org,
	Jonathan Nieder <jrnieder@...il.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org
Subject: Re: CPU hyperthreading turned on after soft power-cycle


>>>> Finally! After another 50+ compilations a have it! It took some time as
>>>> first I had to find a reason why some revisions did not boot (almost 2/3
>>>> were unbootable and the first bad commit was among them). Having this
>>>> solved I have been able to bisect without "skipping". The result is
>>>> surprising (at least for me) - believe it or not, the first bad commit
>>>> is 6610e089 "RTC: Rework RTC code to use timerqueue for events" from
>>>> John Stultz (I am sending him a copy of this message).
>>>>
>>>> I would never expect this would be a problem, but my understanding of
>>>> this commit is very limited, so I am certainly missing the point.
>>>> However, I have tried to compile 2.6.38 (which was "bad") with "Real
>>>> Time Clock" configuration option turned off and it behaves "normally"
>>>> then (= is "good").
>>>
>>> Huh. That's *very* odd.  Is your system doing anything in-particular
>>> with the RTC?  I don't have a clue right off, so probably the next step
>>
>> Yes, it is very odd. The system does not do anything special with RTC.
>> It is a diskless computational workstation.
>>
>>> is doing a bit of instrumentation to try to figure out where exactly we
>>> trigger the behavior. Could you checkout commit 6610e089 and apply the
>>> patch below to see if we can't narrow it down?
>>
>> With the patch applied the system does not show the strange behavior (=
>> is "good").
>>
>>> Could you also send your .config to me?
>>
>> Sure. It is attached. I have found that if I turn CONFIG_RTC_DRV_CMOS
>> off, the system behaves normally (= is "good") too.
>
> Yea. My rough guess is that the BIOS is somehow sensitive to how the
> CMOS RTC is touched.
>
> Does disabling CONFIG_HPET_EMULATE_RTC change the behavior?

But how do I do it? :-)

I have not found a way to disable it in "menuconfig". If I comment it 
out manually in .config, it is automatically set back to "y" as soon as 
compilation starts ...

Thanks,

Jiri


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