Date:   Thu, 17 Feb 2022 12:11:27 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     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>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH 1/2] thermal: cooling: Check Energy Model type in
 cpufreq_cooling and devfreq_cooling



On 2/17/22 11:28 AM, Daniel Lezcano wrote:
> On 17/02/2022 11:47, Lukasz Luba wrote:
>> Hi Daniel,
>>
>> On 2/17/22 10:10 AM, Daniel Lezcano wrote:
>>> On 16/02/2022 18:33, 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.
>>>>>
>>>>> 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.
>>>>
>>>> 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...
>>>
>>> The dynamic-power-coefficient is available for OPPs which includes 
>>> CPUfreq and devfreq. As the GPU is managed by devfreq, setting the 
>>> dynamic-power-coefficient makes the energy model available for it.
>>>
>>> However, the OPPs must define the frequency and the voltage. That is 
>>> the case for most platforms except on QCom platform.
>>>
>>> That may not be specified as it uses a frequency index and the 
>>> hardware does the voltage change in our back. The QCom cpufreq 
>>> backend get the voltage table from a register (or whatever) and 
>>> completes the voltage values for the OPPs, thus adding the 
>>> information which is missing in the device tree. The energy model can 
>>> then initializes itself and allows the usage of the Energy Aware 
>>> Scheduler.
>>>
>>> However this piece of code is missing for the GPU part.
>>>
>>
>> Thank you for joining the discussion. I don't know about that Qcom
>> GPU voltage information is missing.
>>
>> If the voltage is not available (only the frequencies), there is
>> another way. There is an 'advanced' EM which uses registration function:
>> em_dev_register_perf_domain(). It uses a local driver callback to get
>> power for each found frequency. It has benefit because there is no
>> restriction to 'fit' into the math formula, instead just avg power
>> values can be feed into EM. It's called 'advanced' EM [1].
>>
>> Now we hit (again) the DT & EM issue (it's an old one, IIRC Morten
>> was proposing from ~2014 this upstream, but EAS wasn't merged back
>> then):
>> where to store these power-freq values, which are then used by the
>> callback. 
> 
> Why not make it more generic and replace the frequency by a performance 
> index, so it can be used by any kind of perf limiter?

For that DT array, yes, it can be an index, so effectively it could be
a simple 1d array.

something like:

msm_gpu_energy_model: msm-gpu-energy-model {
	compatible = "energy-model"
	/* Values are sorted micro-Watts which correspond to each OPP
	   or performance state. The total amount of them must match
	   number of OPPs. */
	power-microwatt = <100000>,
			<230000>,
			<380000>,
			<600000>;
};

then in gpu node instead of having 'dynamic-power-coefficient',
which is useless because voltage is missing, we would have
'energy-model', like:

	energy-model = <&msm_gpu_energy_model>;


If you agree to continue this topic. I will send an RFC so we could
further discuss this idea. This $subject doesn't fit well.

Thank you again for your feedback Daniel!

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