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

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Message-ID: <6f15ef88-aa9e-4a3c-4a75-1d3216d734d5@osg.samsung.com>
Date:   Thu, 17 Nov 2016 12:40:41 -0300
From:   Javier Martinez Canillas <javier@....samsung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Kukjin Kim <kgene@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Ben Dooks <ben.dooks@...ethink.co.uk>,
        Lee Jones <lee.jones@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Tomasz Figa <tomasz.figa@...il.com>
Subject: Re: [PATCH] ARM: Drop fixed 200 Hz timer requirement from Exynos
 platforms

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@...aro.org>
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> 
> ---
> 
> 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@....samsung.com>

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