linux-kernel - Re: [PATCH 1/2] thermal: cooling: Check Energy Model type in cpufreq_cooling and devfreq

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Date:   Thu, 17 Feb 2022 10:59:12 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Matthias Kaehlcke <mka@...omium.org>,
        Doug Anderson <dianders@...omium.org>
Cc:     Lukasz Luba <lukasz.luba@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        amit daniel kachhap <amit.kachhap@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Amit Kucheria <amitk@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Pierre.Gondois@....com, Stephen Boyd <swboyd@...omium.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH 1/2] thermal: cooling: Check Energy Model type in
 cpufreq_cooling and devfreq_cooling

On 16/02/2022 23:13, Matthias Kaehlcke wrote:
> On Wed, Feb 16, 2022 at 09:33:50AM -0800, Doug Anderson wrote:
>> Hi,
>>
>> On Wed, Feb 16, 2022 at 7:35 AM Lukasz Luba <lukasz.luba@....com> wrote:
>>>
>>> Hi Matthias,
>>>
>>> On 2/9/22 10:17 PM, Matthias Kaehlcke wrote:
>>>> On Wed, Feb 09, 2022 at 11:16:36AM +0000, Lukasz Luba wrote:
>>>>>
>>>>>
>>>>> On 2/8/22 5:25 PM, Matthias Kaehlcke wrote:
>>>>>> On Tue, Feb 08, 2022 at 09:32:28AM +0000, Lukasz Luba wrote:
>>>>>>>
>>>>>>>
>>>
>>> [snip]
>>>
>>>>>>> Could you point me to those devices please?
>>>>>>
>>>>>> arch/arm64/boot/dts/qcom/sc7180-trogdor-*
>>>>>>
>>>>>> Though as per above they shouldn't be impacted by your change, since the
>>>>>> CPUs always pretend to use milli-Watts.
>>>>>>
>>>>>> [skipped some questions/answers since sc7180 isn't actually impacted by
>>>>>>     the change]
>>>>>
>>>>> Thank you Matthias. I will investigate your setup to get better
>>>>> understanding.
>>>>
>>>> Thanks!
>>>>
>>>
>>> I've checked those DT files and related code.
>>> As you already said, this patch is safe for them.
>>> So we can apply it IMO.
>>>
>>>
>>> -------------Off-topic------------------
>>> Not in $subject comments:
>>>
>>> AFAICS based on two files which define thermal zones:
>>> sc7180-trogdor-homestar.dtsi
>>> sc7180-trogdor-coachz.dtsi
>>>
>>> only the 'big' cores are used as cooling devices in the
>>> 'skin_temp_thermal' - the CPU6 and CPU7.
>>>
>>> I assume you don't want to model at all the power usage
>>> from the Little cluster (which is quite big: 6 CPUs), do you?
>>> I can see that the Little CPUs have small dyn-power-coeff
>>> ~30% of the big and lower max freq, but still might be worth
>>> to add them to IPA. You might give them more 'weight', to
>>> make sure they receive more power during power split.
> 
> In experiments we saw that including the little cores as cooling
> devices for 'skin_temp_thermal' didn't have a significant impact on
> thermals, so we left them out.

I agree, that was also my conclusion after doing some measurements.

Basically, the little cores are always cold and are victims of the big 
cores heat dissipation.

They of course contribute a bit to the heat but capping their 
performance does not change the temperature trend of the whole.

That is less true with silver-gold were it is the same micro-arch but 
different frequencies.


>>> You also don't have GPU cooling device in that thermal zone.
>>> Based on my experience if your GPU is a power hungry one,
>>> e.g. 2-4Watts, you might get better results when you model
>>> this 'hot' device (which impacts your temp sensor reported value).
>>
>> I think the two boards you point at (homestar and coachz) are just the
>> two that override the default defined in the SoC dtsi file. If you
>> look in sc7180.dtsi you'll see 'gpuss1-thermal' which has a cooling
>> map. You can also see the cooling maps for the littles.
> 
> Yep, plus thermal zones with cooling maps for the big cores.
> 
>> I guess we don't have a `dynamic-power-coefficient` for the GPU,
>> though? Seems like we should, but I haven't dug through all the code
>> here...
> 
> To my knowledge the SC7x80 GPU doesn't register an energy model, which is
> one of the reasons the GPU wasn't included as cooling device for
> 'skin_temp_thermal'.




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