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

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Message-ID: <1321574019.25715.52.camel@work-vm>
Date:	Thu, 17 Nov 2011 15:53:39 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Jiri Polach <clarinet@...as.cz>
Cc:	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

On Fri, 2011-11-18 at 00:42 +0100, Jiri Polach wrote:
> On 11/17/2011 9:32 PM, John Stultz wrote:
> > On Wed, 2011-11-16 at 23:49 +0100, Clarinet wrote:
> >> Hi all,
> >>
> >>>> Result of bisecting: v2.6.38-rc1 exhibits the problem. v2.6.37 and
> >>>> many of the topic branches merged in the 2.6.38 merge window work ok.
> >>>> Some other topic branches do not boot at all.
> >>>>
> >>>> Jiri: if you have gitk installed, then "git bisect visualize" can help
> >>>> get a sense of what's in the middle of the regression range.
> >>>> "gitk --bisect --first-parent v2.6.37..v2.6.38-rc1" might be a good way
> >>>> to find mainline commits to test before finding a topic branch to delve
> >>>> into.
> >>>
> >>> I have been able to narrow the interval manually a little bit from the
> >>> "top" (the bad side) and I will go on from the bottom now. However,
> >>> there seems to be a large area where kernels are unbootable for me -
> >>> they mostly stop when init is called and I do not know why.
> >>
> >> 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?

thanks
-john




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