On 2021-03-19 14:35, Daniel Lezcano wrote:

Hi Robin,

On 19/03/2021 13:17, Robin Murphy wrote:

quoted

On 2021-03-19 11:05, Daniel Lezcano wrote:

quoted

The DTPM framework is looking for upstream SoC candidates to share the
power numbers.

We can see around different numbers but the one which seems to be
consistent with the initial post for the values on the CPUs can be
found in the patch https://lore.kernel.org/patchwork/patch/810159/

The kernel hacker in me would be more inclined to trust the BSP that the
vendor actively supports than a 5-year-old patch that was never pursued
upstream. Apparently that was last updated more recently:

https://github.com/rockchip-linux/kernel/commit/98d4505e1bd62ff028bd79fbd8284d64b6f468f8

Yes, I've seen this value also.

quoted

The ex-mathematician in me can't even comment either way without
evidence that whatever model expects to consume this value is even
comparable to whatever "arm,mali-simple-power-model" is. >
The way the
latter apparently needs an explicit "static" coefficient as well as a
"dynamic" one, and the value here being nearly 3 times that of a
similarly-named one in active use downstream (ChromeOS appears to still
be using the values from before the above commit), certainly incline me
to think they may not be...

Sorry, I'm missing the point :/

We dropped in the kernel any static power computation because as there
was no value, the resulting code was considered dead. So we rely on the
dynamic power only.

Right, so a 2-factor model is clearly not identical to a 1-factor model, 
so how do we know that a value for one is valid for the other, even if 
it happens to have a similar name? I'm not saying that it is or isn't; I 
don't know. If someone can point to the downstream coefficient 
definition being identical to the upstream one then great, let's use 
that as justification. If not, then the justification of one arbitrary 
meaningless number over any other is a bit misleading.

quoted

quoted

I don't know the precision of this value but it is better than
nothing.

But is it? If it leads to some throttling mechanism kicking in and
crippling GPU performance because it's massively overestimating power
consumption, that would be objectively worse for most users, no?

No because there is no sustainable power specified for the thermal zones
related to the GPU.

OK, that's some reassurance at least. Does the exact value have any 
material effect? If not, what's to stop us from using an obviously 
made-up value like 1, and saying so?

Robin.

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