Configure RPi/RPi2 platform with optimal CPU and IO settings

[MilhouseVH]

The following settings are (or are about to become) the default on other distributions (Raspbian, OSMC etc.) and it is recommended they should also be the default for OpenELEC too:

echo 1 > /sys/devices/system/cpu/cpufreq/ondemand/io_is_busy
echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo 50 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
echo 100000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate
echo 50 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor

The existing values are:

rpi22:~ # cat /sys/devices/system/cpu/cpufreq/ondemand/io_is_busy
0
rpi22:~ # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
ondemand
rpi22:~ # cat /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
50
rpi22:~ # cat /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate
355000
rpi22:~ # cat /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor
1

up_threshold is also being set (to 50) by the cpufreq-threshold service - if this is only for the benefit of the RPi/RPi2, then this service could be eliminated (I can squash removal into this PR, if desired).

This should be OK for master.

[popcornmix]

I can confirm these are the planned default settings for raspbian.

It should improve general performance a little by engaging turbo mode more often.

The io_is_busy setting is important for the new "sdhost" driver which is currently optionally available (by adding dtoverlay=sdhost to config.txt), but we'd like to switch to it being the default after further testing.

Without that setting "sdhost" performance can be reduced when not in turbo mode.

[stefansaraev]

ack from me

up_threshold is also being set (to 50) by the cpufreq-threshold service

not sure, it's probably good for imx6/wetek, too. I'd keep it as is for now.

[MilhouseVH]

I'd keep it as is for now.

Fortunately it's using the same value that the RPi/RPi2 needs, but it's easy to see how it could become a problem if a different value is required. In future perhaps it should be moved to platform_init for imx6/wetek.

[stefansaraev]

Fortunately it's using the same value that the RPi/RPi2 needs

thats right, I'll take care when this PR is merged. just ping me ;)

[MilhouseVH]

Thanks, will do.

BTW, to see the impact of io_is_busy (aka turbo) at higher core overclocks when using the new sdhost driver, I posted the results of a very simple benchmark here, documenting the performance of the old and new driver at different clock settings, with and without turbo.

[sraue]

@MilhouseVH can you change the copyright line in both files :-) other than that if it works it has my ok

[MilhouseVH]

Done, good catch. :)

Yes, tested on both RPi and RPi2 - both working as expected.