Architected timer not being used by default on Arndale

Hi,
The Exynos 5250 includes an architected timer which is on core and very cheap to read.

This appears on dmesg on bootup, but is not in use by default:
# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
mct-frc

We can manually enable the architected timer via:
# echo "arch_sys_counter" > /sys/devices/system/clocksource/clocksource0/current_clocksource
Switching to clocksource arch_sys_counter

Enabling the architected timer can lead to a significant performance improvement for timer sensitive workloads such as TCP/IP.

It turns out that both arch_sys_counter and mct-frc have a rating of 400.
On bootup, arch_sys_counter is initialised first then the clocksource changes to mct-frc when that initialises later on.

If the rating of mct-frc is reduced below 400 (in arch/arm/mach-exynos/mct.c) , then arch_sys_counter becomes the default.

Best,
--
Steve

(This applies to the latest linaro tracking tree).