linux-kernel - Re: Regression in 4.8 - CPU speed set very low

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Date:   Mon, 26 Sep 2016 19:48:23 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: Regression in 4.8 - CPU speed set very low

On 09/26/2016 07:21 PM, Rafael J. Wysocki wrote:
> On Tue, Sep 27, 2016 at 1:53 AM, Larry Finger <Larry.Finger@...inger.net> wrote:
>> On 09/26/2016 05:16 PM, Rafael J. Wysocki wrote:
>>>
>>> On Tue, Sep 27, 2016 at 12:09 AM, Larry Finger
>>
>> <Larry.Finger@...inger.net> wrote:
>>>
>>>
>>> Maybe it's better to try diagnose the problem instead of spending more
>>> time on bisection.
>>
>>
>> In my original post, I asked for such help, but nothing until today. I had
>> no idea what to check, but now I have a better idea.
>>
>>> I'd like to know whether or not 4.7 was definitely good, though.
>>
>>
>> I never saw this problem with 4.7, but given the difficulty in triggering
>> the problem, my tests may not have been definitive.
>>>
>>>
>>>> If it is one of them, it may be a while before I dare call this one
>>>> "good".
>>>> In one respect, that is good as I will be traveling tomorrow and
>>>> Wednesday.
>>>
>>>
>>> What does "cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver" say?
>>
>>
>> intel_pstate
>
> You probably don't need to worry about all of the cpufreq changes in
> 4.8-rc, then.  Only a few of them affect intel_pstate and I don't see
> how any of them may lead to the observed symptoms.
>
> First off, if you have a reproducer, please run it on 4.7 and see if
> you can trigger the issue in there.

I'm running 4.8-rc7 at the moment hoping to trigger the problem and get the data 
requested by Srinivas. Once I get that, I will try 4.7 again.
>
> Second, it would be good to have a look at the output from the
> cpu_frequency and pstate_sample tracepoints around when the issue
> triggers.  The pstate_sample one would be more interesting.
>
> But for both we need a reproducer anyway.

I do not have a reliable reproducer. The condition has always happened when 
running a high-compute job such as a 'make -j8' on the kernel, or building the 
RPM for openSUSE's implementation of VirtualBox. The latter is what I'm using 
for most of my testing.

> It also would be good to rule out the thermal throttling (as per the
> Srinivas' comments).
>
> For now, please tell me what's in
> /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq

800000

Larry