Regression in 4.8 - CPU speed set very low

From	Larry Finger <Larry.Finger@lwfinger.net>
Newsgroups	linux.kernel
Subject	Regression in 4.8 - CPU speed set very low
Date	2016-09-09 19:40 +0200
Message-ID	<sfxWp-5Vo-3@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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I have found a regression in kernel 4.8-rc2 that causes the speed of my laptop 
with an Intel(R) Core(TM) i7-4600M CPU @ 2.90GHz to suddenly have a maximum cpu 
frequency of ~400 MHz. Unfortunately, I do not know how to trigger this problem, 
thus a bisection is not possible. It usually happens under heavy load, such as a 
kernel build or the RPM build of VirtualBox, but it does not always fail with 
these loads. In my most recent failure, 'hwinfo --cpu' reports cpu MHz of 
396.130 for #3. The bogomips value is 5787.73, and the cpu clock before the 
fault is 3437 MHz. Nothing is logged when this happens.

If I were to get a patch that would show a backtrace when the maximum CPU 
frequency is changed, perhaps it would be possible to track this bug.

Sorry that I can not be more specific.

Larry

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Regression in 4.8 - CPU speed set very low Larry Finger <Larry.Finger@lwfinger.net> - 2016-09-09 19:40 +0200
  Re: Regression in 4.8 - CPU speed set very low Larry Finger <Larry.Finger@lwfinger.net> - 2016-09-14 18:10 +0200
    Re: Regression in 4.8 - CPU speed set very low Larry Finger <Larry.Finger@lwfinger.net> - 2016-09-19 05:00 +0200

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