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

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Message-ID: <5271ed6f-5798-e930-d7fd-17fe6bb7ea96@lwfinger.net>
Date:   Wed, 28 Sep 2016 21:22:59 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Doug Smythies <dsmythies@...us.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "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 09/27/2016 06:46 AM, Rafael J. Wysocki wrote:
> On Tue, Sep 27, 2016 at 10:48 AM, Larry Finger
> <Larry.Finger@...inger.net> wrote:
>> On 09/26/2016 10:12 PM, Doug Smythies wrote:
>>>
>>> On 2016.09.26 18:31 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 wrote:
>>>>>> 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.
>>>
>>>
>>> Run some CPU stressor and get all your CPU's going at 100% load.
>>> And watch your core temperatures while you do so.
>>
>>
>> for i in 1 2 3 4; do while : ; do : ; done & done
>>
>> triggered the fault in a few minutes.
>>>
>>>
>>>>
>>>>>> It also would be good to rule out the thermal throttling (as per
>>>>>> the Srinivas' comments).
>>>
>>>
>>> It is almost certainly thermal throttling, or similar causing
>>> Clock modulation, of it seems 50%.
>>
>>
>> While the infinite loops were running, the temps were:
>>
>> finger@...ux-1t8h:~/rtlwifi_new> sensors
>> coretemp-isa-0000
>> Adapter: ISA adapter
>> Physical id 0:  +83.0°C  (high = +84.0°C, crit = +100.0°C)
>> Core 0:         +83.0°C  (high = +84.0°C, crit = +100.0°C)
>> Core 1:         +74.0°C  (high = +84.0°C, crit = +100.0°C)
>
> It looks like the trip point (high) temperature was exceeded causing
> thermal throttling to kick in.
>
>> After the fault occurs, I get
>>
>> finger@...ux-1t8h:~/rtlwifi_new> sensors
>> coretemp-isa-0000
>> Adapter: ISA adapter
>> Physical id 0:  +44.0°C  (high = +84.0°C, crit = +100.0°C)
>> Core 0:         +43.0°C  (high = +84.0°C, crit = +100.0°C)
>> Core 1:         +41.0°C  (high = +84.0°C, crit = +100.0°C)
>
> So after that it stays at 400 MHz forever, right?
>
>>>>>>
>>>>>> 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?
>>>
>>>
>>> And what make and model of LapTop?
>>
>>
>> Toshiba Tecra A50-A with CPU Model: 6.60.3 "Intel(R) Core(TM) i7-4600M CPU @
>> 2.90GHz. That is a dual-core unit with hyperthreading.
>>
>> @Rafael: As I write this, the system has been running the infinite loop test
>> for almost 5 hours with kernel 4.7. I will leave that running while I'm
>> gone, but I am certain that it is OK.
>
> OK, and what temperatures do you see while doing this?

finger@...ux-1t8h:~/linux-2.6> sensors
coretemp-isa-0000
Adapter: ISA adapter
Physical id 0:  +90.0°C  (high = +84.0°C, crit = +100.0°C)
Core 0:         +90.0°C  (high = +84.0°C, crit = +100.0°C)
Core 1:         +78.0°C  (high = +84.0°C, crit = +100.0°C)

Once again, the CPU temp is greater than the "high" value; however, the clock 
rate continues to hold near 3600 MHz.

My laptop was inadvertently put to sleep while I was gone. I forgot to leave a 
note for my wife and she quieted the noisy cpu fan. :)

Larry