Re: [PATCH 1/2] thermal: cooling: Check Energy Model type in cpufreq_cooling and devfreq_cooling

[Daniel Lezcano]

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@xxxxxxx> 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?

> 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 


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