Re: [Discuss-gnuradio] Performance on ARM Cortex-A8

[Nick Foster]

On Fri, 2011-07-15 at 16:24 -0400, Marcus D. Leech wrote:
> On 07/13/2011 04:40 AM, Riadh Elloumi wrote:
> > Hi all,
> >
> > I complied DAB demodulation for ARM Cortex-A8 (TI OMAP 3). It
> > successfully demodulate DAB+ but spends 13 seconds decoding 1 second of
> > radio baseband (USRP file).
> >
> > I used all the optimized code for Cortex-A8 like dotprod_ccf_armv7_a.c.
> > My compilation flags are: -mcpu=cortex-a8 -mfloat-abi=softfp -mfpu=neon
> > -O2. I used fftw-3.2.2.
> What does -mfloat-abi=softfp do?  Does that cause software 
> floating-point to be used?
>    If it does, then your floating-point performance is going to be 
> completely awful.

Counterintuitively, that flag doesn't mean "use emulated fp". However,
gcc is notoriously bad at vectorizing code for the NEON vfpu. The
upcoming Volkification of gnuradio-core will hopefully do a lot to
improve E100 performance on CPU-intensive flowgraphs.

--n

> 
> A good test for comparing oranges/oranges would be to construct  simple 
> C program
>    that does, let's say, 10e6 single-precision floating-point 
> multiply/accumulate operations,
>    and compare among platforms with simiilar clock speeds, etc.
> 
> > Why is gnu radio too slow demodulating DAB+? Do you have some figures of
> > CPU consumption on ARM Cortex cores? Is there some optimization I missed
> > for the platform?
> >
> >
> 
>