Messages in this thread | | | Subject | Re: Regression in 4.8 - CPU speed set very low | From | Larry Finger <> | Date | Wed, 28 Sep 2016 21:26:42 -0500 |
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On 09/27/2016 09:51 AM, Lennart Sorensen wrote: > On Mon, Sep 26, 2016 at 04:28:29PM -0500, Larry Finger wrote: >> Mostly I use a KDE applet named "System load" and look at the "average >> clock", but the same info is also available in /proc/cpuinfo as "cpu MHz". >> When the bug triggers, the system gets very slow, and the cpu fan stops even >> though the cpu is still busy. >> >> Commit f7816ad, which had run for 7 days without showing the bug, failed >> after about 2 hours today. All my testing since Sept. 9 has been wasted. Oh >> well, that's the way it goes! > > Is it possible there is no bug and instead you have a hardware problem? > > What I am thinking: > > CPU fan stops, then CPU gets busy, CPU overheats, thermal throtling > kicks in to protect CPU and it gets VERY slow. > > So maybe you have a bad CPU fan that is getting stuck. Perhaps even if > you have a motherboard that varies the CPU fan depending on need and the > fan doesn't like the lowest speed and sometimes gets stuck when asked > to go slow. > > Of course if the CPU fan is the problem that could explain why it takes > varying amounts of time to see the problem. > > I suggest checking what the cpu temperature sensors are showing next > time it gets slow.
By the time it gets slow, the CPU's cool, and one cannot see the temp just before that event happened.
The reason I suspect a bug is that it fails with 4.8-rcX, but not with 4.7. Of course, it could be something subtle that slightly changes the heat load, which causes the CPU temp to be a little higher so that the effect is triggered.
I am reasonably confident that it is not a hardware problem, but we may have to wait until 4.8 is released and gets wider usage. If no one else reports a problem, then I am certainly wrong.
Larry
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