Messages in this thread | | | Subject | Re: Regression in 4.8 - CPU speed set very low | From | Larry Finger <> | Date | Sun, 18 Sep 2016 21:54:55 -0500 |
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On 09/14/2016 11:00 AM, Larry Finger wrote: > 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.
And still does. My bisection seemed to be trending toward an improbable set of commits, and I needed to do some other work with the machine, thus I started running 4.8-rc6. It failed nearly 48 hours after the reboot, which indicated that using 3 days to indicate a "good" trial was likely too short. I am currently testing the first of the trial and will run it for at least a week. It is unlikely that these tests will be complete before 4,8 is released, even if -rc8 is needed. I will keep attempting to find the faulty commit.
Larry
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