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Re: [Discuss-gnuradio] Beagle board update
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] Beagle board update |
Date: |
Fri, 24 Oct 2008 08:31:43 -0700 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
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