Re: [Discuss-gnuradio] Beagle board update

[Eric Blossom]

On Fri, Oct 24, 2008 at 08:19:49AM -0700, Philip Balister wrote:
> On Fri, Oct 24, 2008 at 6:27 AM, Eric Blossom <address@hidden> wrote:

> >> address@hidden:/home/balister/oe/tmp/work/armv7a-angstrom-linux-gnueabi/gnuradio-3.1.3+svnr9809-r4.1/trunk/gnuradio-core/src/tests#
> >> ./benchmark_dotprod_fff
> >>     generic: taps:  256  input: 4e+07  cpu: 968.586  taps/sec:  1.057e+07
> >>  cortex_a8: taps:  256  input: 4e+07  cpu: 45.703    taps/sec:  2.241e+08
> >>
> >> Philip
> >
> > Cool!
> >
> > The good news / bad news is that the spread is worse than on the P4!
> >
> > Is there a way to get the compiler to use the NEON instruction set in
> > scalar mode?  E.g., something like -mfpmath=sse on x86?  Maybe -mfp=vfp?
> > Are you providing the -mcpu=cortex-a8 gcc option?
> 
> The Cortex-A8 numbers use assembler to unroll the inner loop 8 times.
> I think this code can get better. I'll have to double check the flags,
> but I do not think gcc does a good job generating code for the
> vfp/NEON unit. (We are happy gcc can generate anything supporting NEON
> and not crash ...)
> 
> Remember, this is clocked at 600 MHz and consumes about 1 Watt.

Understood.  I'm trying to keep you out of the assembly business.  The
fact that your assembly code is 20 time faster is scary.  That's why I
was asking about compiler flags.  I suspect that you're not telling
gcc enough about the machine.

Eric