linux-kernel - Re: [PATCH] Fix mt7622.dtsi thermal cpu

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Message-ID: <e30a2d01-a200-80cb-88d9-6aea62dd49f1@linaro.org>
Date:   Mon, 21 Jun 2021 20:29:13 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     ericwouds@...il.com, Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix mt7622.dtsi thermal cpu

On 19/06/2021 14:19, ericwouds@...il.com wrote:
> From: Eric Woudstra <ericwouds@...il.com>
> 
> Cpu-thermal is set to use all frequencies already at 47 degrees. 
> Using the CPU at 50 for a minute, the CPU has reached 48 degrees, is 
> throttled back to lowest setting, making the mt7622 terrribly slow. 
> Even at this low speed, the CPU does not cool down lower then 47 so
> the CPU is stuck at lowest possible frequency until it shut down and
> stays off for 15 minutes.
> 
> cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
>                  <&cpu1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
> 
> This should not be set al every cooling map. It should only be set at
> the highest cooling map. Same as in the example:
> 
> https://www.kernel.org/doc/Documentation/devicetree/bindings/
> thermal/thermal.txt  line 272
> 
> But then without the fan and added a third map.
> 
> Now temperature will be regulated at 87 degrees celcius. At temperatures
> lower then 87, all frequencies can be used.

47°C is really a too low temperature and this performance drop is normal.

I would not remove the passive mitigation but try by increasing the CPU
temp to 70°C and by changing the active trip point to 80°C. If it works
fine, try 75°C and 85°C.

To test, the thermal killer is dhrystone (one thread per cpu).

With a 75°C passive trip point, the step wise thermal governor, I think
the mitigation will happen smoothly providing better performances, and
probably the fan won't fire.

> Also see the post:
> 
> http://forum.banana-pi.org/t/bpi-r64-only-10-cpu-speed-at-already-48-
> degrees-celcius-speed-not-increasing-anymore/12262
> 
> Signed-off-by: Eric Woudstra <ericwouds@...il.com>
> ---
>  arch/arm64/boot/dts/mediatek/mt7622.dtsi | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/mediatek/mt7622.dtsi b/arch/arm64/boot/dts/mediatek/mt7622.dtsi
> index 890a942ec..b779c7aa6 100644
> --- a/arch/arm64/boot/dts/mediatek/mt7622.dtsi
> +++ b/arch/arm64/boot/dts/mediatek/mt7622.dtsi
> @@ -170,14 +170,14 @@ cpu-crit {
>  			cooling-maps {
>  				map0 {
>  					trip = <&cpu_passive>;
> -					cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> -							 <&cpu1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
> +					cooling-device = <&cpu0 0 0>,
> +							 <&cpu1 0 0>;
>  				};
>  
>  				map1 {
>  					trip = <&cpu_active>;
> -					cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> -							 <&cpu1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
> +					cooling-device = <&cpu0 0 0>,
> +							 <&cpu1 0 0>;
>  				};
>  
>  				map2 {
> 


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