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

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Message-ID: <CAJZ5v0j3fJ7pDoR+LhY6x1T0yQEhq6omFL7-BrBcMy68eFiMMg@mail.gmail.com>
Date:   Tue, 27 Sep 2016 13:46:13 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Larry Finger <Larry.Finger@...inger.net>
Cc:     Doug Smythies <dsmythies@...us.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "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>
Subject: Re: Regression in 4.8 - CPU speed set very low

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?

Thanks,
Rafael