I've been trying to figure out why OpenEmbedded on beaglebone is three
times slower than Debian on the ray-tracing application described at:
http://scruss.com/blog/2013/09/23/beaglebone-black-slow-as-a-dog/
Part of it is due to meta-yocto-bsp's beaglebone config not enabling CPU
frequency control (CONFIG_GENERIC_CPUFREQ_CPU0,
CONFIG_VOLTAGE_DOMAIN_OMAP, and some THERMAL options). That can be
fixed for linux-yocto, and isn't an issue with linux-ti-staging, but it
doesn't eliminate the discrepancies.
With debian, the sample program described in that blog posting runs this
fast:
debian@beaglebone:~$ g++ -Ofast -mfloat-abi=hard -o card card.cpp
debian@beaglebone:~$ time ./card > /dev/null
real 4m54.846s
user 4m54.627s
sys 0m0.057s
With poky master + meta-ti it runs this fast:
root@beaglebone:~# time ./card > /dev/null
real 9m37.901s
user 9m37.200s
sys 0m0.150s
Still nearly twice as slow. (With linux-yocto and the default kernel
configuration it's up around 14m.)
One anomaly I've found is the CPU frequency range. On debian we have:
debian@beaglebone:~$ cat
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
300000 600000 800000 1000000
while on OE we have:
root@beaglebone:~# cat
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
300000 600000 720000 800000
So OE isn't allowing the BeagleBoneBlack to run at its maximum speed.
This isn't enough to explain a nearly 2x performance difference, but
it's an issue I want resolved.
I've been unable to trace back where these frequencies come from. Could
somebody tell me what configures the available frequencies for the
AM335x in linux-ti-staging?
And if anybody has suggestions of where else to look for an explanation,
I'd appreciate it. I've tried all the gcc flags I can think of
(-mcpu=cortex-a8, -mfpu=neon, -mfloat-abi=hard, etc), though I'm going
to keep poking at it because I still suspect the problem is there.
Thanks.
Peter
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