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SubjectRe: [PATCH] arm64: dts: meson: Add capacity-dmips-mhz attributes to GXM
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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@gmail.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@baylibre.com>

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