Re: [PATCH] ARM: Drop fixed 200 Hz timer requirement from Exynos platforms

From: Javier Martinez Canillas
Date: Thu Nov 17 2016 - 12:32:43 EST

Hello Krzysztof,

On 11/14/2016 03:27 PM, 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 selected.
> 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. In
> fact Exynos can work with different timers.
> 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>
> Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
> ---
> Testing on other Exynos platforms would be appreciated.

I tested this patch on an Exynos5800 Peach Pi Chromebook with different
HZ values (100/200/250/300/500/1000), and found no issues.

Tested-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>

Best regards,
Javier Martinez Canillas
Open Source Group
Samsung Research America