linux-kernel - Re: [PATCH] arm64: dts: meson: Add capacity-dmips-mhz attributes to GXM

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Message-ID: <c5656549-6c99-95b5-0cdb-a9f1a5d538e0@baylibre.com>
Date:   Tue, 24 Nov 2020 14:24:13 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Christian Hewitt <christianshewitt@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kevin Hilman <khilman@...libre.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: meson: Add capacity-dmips-mhz attributes to
 GXM

On 24/11/2020 13:17, Christian Hewitt wrote:
> GXM (S912) is a big-little design with CPUs 0-3 clocked at 1.5GHz
> and CPUs 4-7 at 1.0GHz. Adding capacity-dmips-mhz attributes allows
> the scheduler to factor the different clock speeds into capacity
> calculations and prefer the higher-clocked cluster to improve
> overall performance.
> 
> This was inspired by the similar change for G12B [0] boards. The
> diference here is that all cores are A53's so the same dmips-mhz
> value is used.
> 
> VIM2:~ # cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq
> 1512000
> 1512000
> 1512000
> 1512000
> 1000000
> 1000000
> 1000000
> 1000000
> 
> before:
> 
> VIM2:~ # cat /sys/devices/system/cpu/cpu*/cpu_capacity
> 1024
> 1024
> 1024
> 1024
> 1024
> 1024
> 1024
> 1024
> 
> after:
> 
> VIM2:~ # cat /sys/devices/system/cpu/cpu*/cpu_capacity
> 1024
> 1024
> 1024
> 1024
> 677
> 677
> 677
> 677
> 
> The after value matches my table-napkin calculation:
> 
> (1000000 / 1512000 = 0.661) * 1024 = 677
> 
> [0] https://github.com/torvalds/linux/commit/6eeaf4d2452ec8b1ece58776812140734fc2e088
> 
> Signed-off-by: Christian Hewitt <christianshewitt@...il.com>
> ---
>  arch/arm64/boot/dts/amlogic/meson-gxm.dtsi | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/amlogic/meson-gxm.dtsi b/arch/arm64/boot/dts/amlogic/meson-gxm.dtsi
> index fe4145112295..411cc312fc62 100644
> --- a/arch/arm64/boot/dts/amlogic/meson-gxm.dtsi
> +++ b/arch/arm64/boot/dts/amlogic/meson-gxm.dtsi
> @@ -42,11 +42,28 @@
>  			};
>  		};
>  
> +		cpu0: cpu@0 {
> +			capacity-dmips-mhz = <1024>;
> +		};
> +
> +		cpu1: cpu@1 {
> +			capacity-dmips-mhz = <1024>;
> +		};
> +
> +		cpu2: cpu@2 {
> +			capacity-dmips-mhz = <1024>;
> +		};
> +
> +		cpu3: cpu@3 {
> +			capacity-dmips-mhz = <1024>;
> +		};
> +
>  		cpu4: cpu@100 {
>  			device_type = "cpu";
>  			compatible = "arm,cortex-a53";
>  			reg = <0x0 0x100>;
>  			enable-method = "psci";
> +			capacity-dmips-mhz = <1024>;
>  			next-level-cache = <&l2>;
>  			clocks = <&scpi_dvfs 1>;
>  			#cooling-cells = <2>;
> @@ -57,6 +74,7 @@
>  			compatible = "arm,cortex-a53";
>  			reg = <0x0 0x101>;
>  			enable-method = "psci";
> +			capacity-dmips-mhz = <1024>;
>  			next-level-cache = <&l2>;
>  			clocks = <&scpi_dvfs 1>;
>  			#cooling-cells = <2>;
> @@ -67,6 +85,7 @@
>  			compatible = "arm,cortex-a53";
>  			reg = <0x0 0x102>;
>  			enable-method = "psci";
> +			capacity-dmips-mhz = <1024>;
>  			next-level-cache = <&l2>;
>  			clocks = <&scpi_dvfs 1>;
>  			#cooling-cells = <2>;
> @@ -77,6 +96,7 @@
>  			compatible = "arm,cortex-a53";
>  			reg = <0x0 0x103>;
>  			enable-method = "psci";
> +			capacity-dmips-mhz = <1024>;
>  			next-level-cache = <&l2>;
>  			clocks = <&scpi_dvfs 1>;
>  			#cooling-cells = <2>;
> 

Re-reading the bindings, the value is correct and necessary to have the cpu_capacity calculated
to help the scheduler.

Thanks!

Reviewed-by: Neil Armstrong <narmstrong@...libre.com>