| Message ID | 1479467712-5218-1-git-send-email-krzk@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Nov 18, 2016 at 01:15:12PM +0200, 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. > > On S3C24xx, the PWM counter is only 16 bit wide, and with the > typical 12MHz input clock that overflows every 5.5ms. This works > with HZ=200 or higher but not with HZ=100 which needs a 10ms > interval between ticks. On Later chips (S3C64xx, S5P and EXYNOS), > the counter is 32 bits and does not have this problem. > > The new samsung_pwm_timer driver solves the problem by scaling the input > clock by a factor of 50 on S3C24xx, which makes it less accurate but > allows HZ=100 as well as CONFIG_NO_HZ with fewer wakeups. > > 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@linaro.org> > [Dropping of 200_HZ from S3C/S5P was suggested by Arnd] > Reported-by: Arnd Bergmann <arnd@arndb.de> > Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org> > Cc: Kukjin Kim <kgene@kernel.org> > [Tested on Exynos5800] > Tested-by: Javier Martinez Canillas <javier@osg.samsung.com> > Acked-by: Kukjin Kim <kgene@kernel.org> > [Tested on S3C2440] > Tested-by: Sylwester Nawrocki <s.nawrocki@samsung.com> > > --- > > Changes since v2: > 1. Extend message. > 2. Add Kukjin's ack. > 3. Add Sylwester's tested-by. > > 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(-) > Applied, Krzysztof
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
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. On S3C24xx, the PWM counter is only 16 bit wide, and with the typical 12MHz input clock that overflows every 5.5ms. This works with HZ=200 or higher but not with HZ=100 which needs a 10ms interval between ticks. On Later chips (S3C64xx, S5P and EXYNOS), the counter is 32 bits and does not have this problem. The new samsung_pwm_timer driver solves the problem by scaling the input clock by a factor of 50 on S3C24xx, which makes it less accurate but allows HZ=100 as well as CONFIG_NO_HZ with fewer wakeups. 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@linaro.org> [Dropping of 200_HZ from S3C/S5P was suggested by Arnd] Reported-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org> Cc: Kukjin Kim <kgene@kernel.org> [Tested on Exynos5800] Tested-by: Javier Martinez Canillas <javier@osg.samsung.com> Acked-by: Kukjin Kim <kgene@kernel.org> [Tested on S3C2440] Tested-by: Sylwester Nawrocki <s.nawrocki@samsung.com> --- Changes since v2: 1. Extend message. 2. Add Kukjin's ack. 3. Add Sylwester's tested-by. 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(-)