Re: [PATCH 1/2] thermal: cooling: Check Energy Model type in cpufreq_cooling and devfreq_cooling
From: Lukasz Luba
Date: Thu Feb 17 2022 - 13:05:23 EST
On 2/17/22 5:14 PM, Matthias Kaehlcke wrote:
On Thu, Feb 17, 2022 at 08:37:39AM -0800, Doug Anderson wrote:
Hi,
On Thu, Feb 17, 2022 at 2:47 AM Lukasz Luba <lukasz.luba@xxxxxxx> 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].
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?
Yes, I think for the em_dev_register_perf_domain() route support from
Qualcomm would be needed since "Drivers must provide a callback
function returning <frequency, power> tuples for each performance
state. ".
Not necessarily. It might be done 'generically' by fwk.
There are other benefits of this 'energy-model' entry in the DT.
I'll list them in the cover letter. Let me send an RFC, so we could
discuss there.
Thanks guys!
Regards,
Lukasz