lkml.org 
[lkml]   [2016]   [Sep]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: Regression in 4.8 - CPU speed set very low
    From
    Date
    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


    \
     
     \ /
      Last update: 2016-09-19 04:55    [W:4.309 / U:0.348 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site