linux-kernel - Re: [PATCH] dt: rockchip: rk3399: Add dynamic power coefficient for GPU

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Date:   Fri, 19 Mar 2021 15:35:13 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Robin Murphy <robin.murphy@....com>, heiko@...ech.de
Cc:     Rob Herring <robh+dt@...nel.org>, Johan Jonker <jbx6244@...il.com>,
        Helen Koike <helen.koike@...labora.com>,
        Shunqian Zheng <zhengsq@...k-chips.com>,
        Jacob Chen <jacob2.chen@...k-chips.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Markus Reichl <m.reichl@...etechno.de>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/Rockchip SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC support" 
        <linux-rockchip@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dt: rockchip: rk3399: Add dynamic power coefficient for
 GPU


Hi Robin,

On 19/03/2021 13:17, Robin Murphy wrote:
> On 2021-03-19 11:05, Daniel Lezcano wrote:
>> 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.

> 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.

>> 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.



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