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

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Date:   Tue, 27 Sep 2016 02:21:34 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Larry Finger <Larry.Finger@...inger.net>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "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 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.

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.

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

Thanks,
Rafael