Messages in this thread | | | Subject | Re: Regression in 4.8 - CPU speed set very low | From | Larry Finger <> | Date | Wed, 14 Sep 2016 11:00:23 -0500 |
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On 09/09/2016 12:39 PM, Larry Finger wrote: > 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.
I have not yet found the bad commit, but I have reduced the range of commits a bit. This bug has been difficult to trigger. So far, it has not taken over 1/2 day to appear in bad kernels, thus I am allowing three days before deciding that a given trial is good. I never saw the problem with 4.7 kernels, but I did in 4.8-rc1. I also know that it appeared before commit 581e0cd. Commit 1b05cf6 did not show the bug.
Testing continues.
Larry
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