[fedora-arm] BeagleBone Black CPU speed

[Steve Underwood]

Hi Peter,

On 01/22/2014 04:14 AM, Peter Robinson wrote:
>>> It looks like the BeagleBone Black is still running at 550MHz with the
>>> latest Fedora 20. Does anyone know what is holding it back from running at
>>> 1GHz? Is the a uboot thing, or a kernel thing, or something else? I saw a
>>> version of uboot referred to as making the BBB run at 1GHz, but when I tried
>>> experimenting with that I got the same 550MHz clock speed.
>> If you're interested could you try the kernel-3.13.0-1.1.fc20 scratch
>> kernel [1] on your BBBlack. It should add freq scaling support and you
>> should be able to tell if it detects it appropriately if the
>> cpufreq-cpu0 module loads. Feedback welcome.
> So that kernel works with my testing but the module doesn't auto load
> the cpufreq-cpu0 module. If you do:
>
> modprobe cpufreq-cpu0
>
> You then get:
> cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
> 300000 600000 800000 1000000
>
> Even with 3.12.8 you can manually load that module and it works but
> you only get up to 720mhz.
>
> Peter
>
>> [1] http://pbrobinson.fedorapeople.org/arm-kernel/kernel-3.13.0-1.1.fc20.armv7hl.rpm
Earlier Jos Vos reported the following results for his BeagleBoneBlack 
running pystone.py

Fedora:
Pystone(1.1) time for 50000 passes = 10.9073
This machine benchmarks at 4584.1 pystones/second

Debian:
Pystone(1.1) time for 50000 passes = 4.38
This machine benchmarks at 11415.5 pystones/second


Before this latest kernel I was getting results a few percent slower than he reported for Fedora. With this new kernel RPM I get

Pystone(1.1) time for 50000 passes = 6.23986
This machine benchmarks at 8013.01 pystones/second

That speed is very consistent across runs of the test. The speed has increased, but it seems to still be well below that of Debian. If I use

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

While the machine is idle it says 300MHz. While pystone.py is running it says 1GHz. When the machine is idle, top says the CPU is around 1% loaded. When pystone.py is running it says it is 99.x% loaded. As far as I can tell the clock jumps from 300MHz to 1GHz as pystone.py starts up - i.e there is no substantial lag, resulting in half the test running at 300MHz and half at 1GHz.

If my board really is now running pystone.py at 1GHz, I wonder what else could be causing this test to be around 50% slower than with Debian.

Regards,
Steve