Date:   Thu, 17 Feb 2022 19:27:36 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Doug Anderson <dianders@...omium.org>,
        Lukasz Luba <lukasz.luba@....com>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        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>,
        jorcrous@...zon.com, Rob Clark <robdclark@...omium.org>,
        Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
Subject: Re: [PATCH 1/2] thermal: cooling: Check Energy Model type in
 cpufreq_cooling and devfreq_cooling


Adding Manaf (QCom) in the loop

On 17/02/2022 17:37, Doug Anderson wrote:
> Hi,
> 
> On Thu, Feb 17, 2022 at 2:47 AM Lukasz Luba <lukasz.luba@....com> 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].
> 
> It seems like there _should_ be a way to get the voltage out for GPU
> operating points, like is done with cpufreq in
> qcom_cpufreq_hw_read_lut(), but it might need someone with Qualcomm
> documentation to help with it. Maybe Rajendra would be able to help?
> Adding Jordon and Rob to this conversation in case they're aware of
> anything.
> 
> As you said, we could just list a power for each frequency, though.
> 
> I'm actually not sure which one would be more accurate across a range
> of devices with different "corners": specifying a dynamic power
> coefficient used for all "corners" and then using the actual voltage
> and doing the math, or specifying a power number for each frequency
> and ignoring the actual voltage used. In any case we're trying to get
> ballpark numbers and not every device will be exactly the same, so
> probably it doesn't matter that much.
> 
> 
>> 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. We have the 'dynamic-power-coefficient' in DT, but
>> it has limitations. It would be good to have this simple array
>> attached to the GPU/CPU node. IMHO it meet the requirement of DT,
>> it describes the HW (it would have HZ and Watts values).
>>
>> Doug, Matthias could you have a look at that function and its
>> usage, please [1]?
>> If you guys would support me in this, I would start, with an RFC
>> proposal, a discussion on LKML.
>>
>> [1]
>> https://elixir.bootlin.com/linux/v5.17-rc4/source/Documentation/power/energy-model.rst#L87
> 
> Matthias: I think you've spent more time on the thermal stuff than me
> so I'll assume you'll follow-up here. If not then please yell!
> 
> Ideally, though, someone from Qualcomm would jump in an own this.
> Basically it allows more intelligently throttling the GPU and CPU
> together in tandem instead of treating them separately IIUC, right?
> 
> -Doug


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