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

[Lukasz Luba]

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@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?

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!