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

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Date:   Mon, 26 Sep 2016 21:53:10 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "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>
Subject: Re: Regression in 4.8 - CPU speed set very low

On 09/26/2016 08:30 PM, Srinivas Pandruvada wrote:
> On Mon, 2016-09-26 at 19:48 -0500, Larry Finger wrote:
>> On 09/26/2016 07:21 PM, Rafael J. Wysocki wrote:
>>>
>>> On Tue, Sep 27, 2016 at 1:53 AM, Larry Finger <Larry.Finger@...inge
>>> r.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
> Your effective freq is lower than 800MHz. One of the possible reason is
> thermal throttling.
>
> What distro you are using?

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Larry