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Subject: Re: [PATCH 1/2] thermal: cooling: Check Energy Model type in
 cpufreq_cooling and devfreq_cooling
To:     Matthias Kaehlcke <mka@chromium.org>,
        Doug Anderson <dianders@chromium.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        amit daniel kachhap <amit.kachhap@gmail.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Amit Kucheria <amitk@kernel.org>,
        Zhang Rui <rui.zhang@intel.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Pierre.Gondois@arm.com, Stephen Boyd <swboyd@chromium.org>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>
References: <20220207073036.14901-1-lukasz.luba@arm.com>
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 <4a7d4e94-1461-5bac-5798-29998af9793a@arm.com> <YgKnnFl7Gp8AS30X@google.com>
 <e4532f65-7f8a-7e89-97c1-85cc61462040@arm.com> <YgQ9XLcto9v0fyTf@google.com>
 <d120110a-7d01-0cfd-f7eb-d160e17ec2a8@arm.com>
 <CAD=FV=VntGw1_AzJPpdOk0zSpOVZRH2X1JNg84JX+zCeU1jvXg@mail.gmail.com>
 <Yg13JoHLmeFGPOAW@google.com>
From:   Lukasz Luba <lukasz.luba@arm.com>
Message-ID: <e9ae0530-64bd-3684-1f7d-b496d65d9e70@arm.com>
Date:   Wed, 16 Feb 2022 22:43:34 +0000
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On 2/16/22 10:13 PM, 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@arm.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.
> 
>>> 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'.
> 

You can give it a try by editing the DT and adding in the
GPU node the 'dynamic-power-coefficient' + probably
small modification in the driver code.

If the GPU driver registers the cooling device in the new way, you
would also get EM registered thanks to the devfreq cooling new code
(commit: 84e0d87c9944eb36ae6037a).

You can check an example from Panfrost GPU driver [1].

I can see some upstream MSM GPU driver, but I don't know if that is
your GPU driver. It registers the 'old' way the devfreq cooling [2]
but it would be easy to change to use the new function.
The GPU driver would use the same dev_pm_opp_of_register_em() as
your CPUs do, so EM would be in 'milli-Watts' (so should be fine).


[1] 
https://elixir.bootlin.com/linux/v5.16/source/drivers/gpu/drm/panfrost/panfrost_devfreq.c#L153
[2] 
https://elixir.bootlin.com/linux/v5.16/source/drivers/gpu/drm/msm/msm_gpu_devfreq.c#L129