[Discuss-gnuradio] FFTW --enable-sse and gcc 3.4.4

[Lee Patton]

I am happy to report that FFTW can be built with --enable-sse under
Fedora Core 3 using gcc 3.4.4.

Ignore the rest if this has never been a problem for you...

I originally built FFTW with gcc 3.4.2, and ran into the same problem as
these fine folks:

http://lists.gnu.org/archive/html/discuss-gnuradio/2005-04/msg00070.html

Basically, when running usrp_fft.py, a seg fault would occur in
libfftw3f.so. Building FFTW without --enable-sse using gcc 3.4.2 got rid
of the seg fault. This seemed to be a problem for Fedora Core 3 users
only.

An email from an FFTW developer revealed this was due to bug in gcc
3.4.[0123], and that it should be fixed in gcc 3.4.4.  While all the
reports in this list came from FC3 users, he said he reproduced it under
Debian too.

I never bench marked w/ and w/o SSE enabled. So, I don't know if this is
actually improving performance. Although the FFTW site says it should.

I also noticed that the FFTW configure script thinks I have a Pentium
Pro, when I have the more specific Pentium M.  A Pentium M is based on
Pentium Pro, but supposedly has better SSE support.  I don't know how
true that is or not.  Anyway, I changed the -mcpu=pentiumpro to -
mcpu=pentium-m, and did not notice any appreciable performance increases
in usrp_fftw.py.  The FFTW developer said that the next release of FFTW
will have improved cpu detection support.

Are there standard benchmarking scripts distributed with gnuradio that I
could use to test if changing -mcpu or enabling/disabling SSE makes a
difference?

- Lee