On Fri, 18 Nov 2016, Krzysztof Kozlowski wrote:
> All Samsung platforms, including the Exynos, are selecting HZ_FIXED with
> 200 Hz. Unfortunately in case of multiplatform image this affects also
> other platforms when Exynos is enabled.
>
> This looks like an very old legacy code, dating back to initial
> upstreaming of S3C24xx. Probably it was required for s3c24xx timer
> driver, which was removed in commit ad38bdd15d5b ("ARM: SAMSUNG: Remove
> unused plat-samsung/time.c").
>
> Since then, this fixed 200 Hz spread everywhere, including out-of-tree
> Samsung kernels (SoC vendor's and Tizen's). I believe this choice
> was rather an effect of coincidence instead of conscious choice.
>
> Exynos uses its own MCT or arch timer and can work with all HZ values.
> Older platforms use newer Samsung PWM timer driver which should handle
> down to 100 Hz.
>
> Few perf mem and sched tests on Odroid XU3 board (Exynos5422, 4x Cortex
> A7, 4x Cortex A15) show no regressions when switching from 200 Hz to
> other values.
>
> Reported-by: Lee Jones <lee.jones@xxxxxxxxxx>
Acked-by: Lee Jones <lee.jones@xxxxxxxxxx>
> [Dropping 200_HZ from S3C/S5P suggested by Arnd]
> Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
> Cc: Kukjin Kim <kgene@xxxxxxxxxx>
> Tested-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>
>
> ---
>
> Tested on Exynos5422 and Exynos5800 (by Javier). It would be
> appreciated if anyone could test it on S3C24xx or S5PV210.
>
> Changes since v1:
> 1. Add Javier's tested-by.
> 2. Drop HZ_FIXED also from ARCH_S5PV210 and ARCH_S3C24XX after Arnd
> suggestions and analysis.
> ---
> arch/arm/Kconfig | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index b5d529fdffab..ced2e08a9d08 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1496,8 +1496,7 @@ source kernel/Kconfig.preempt
>
> config HZ_FIXED
> int
> - default 200 if ARCH_EBSA110 || ARCH_S3C24XX || \
> - ARCH_S5PV210 || ARCH_EXYNOS4
> + default 200 if ARCH_EBSA110
> default 128 if SOC_AT91RM9200
> default 0
>
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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