RE: [Discuss-gnuradio] Multi-threaded FFTW

[Bruce Stansby]

When I was originally messing around with multi threading for my application, 
the use of measure gave a large improvement. Though I am using small fft sizes 
(1024) but high data rates. Also it was a custom c program.
________________________________________
From: address@hidden address@hidden on behalf of Marcus D. Leech address@hidden
Sent: Monday, 6 December 2010 3:05 PM
To: address@hidden
Subject: [Discuss-gnuradio] Multi-threaded FFTW

I did some tests tonight using the multi-thread support in FFTW3.

The changes to gri_fft.cc were relatively minor, but plugging this into
the existing build environment
  will require a little surgery, since you need to add -lfftw3f_threads
to the ld flags, and the ld flags
  for FFTW3F are intuited from pkgconfig by default, which doesn't
include support for multi-threaded
  FFTW3F.  I didn't do that surgery, instead manually setting the
FFTW3F_LIBS environment variable
  before calling ./configure, and then doing the build.

On my lowly Centrino-Duo laptop, I was able to measure a 40% throughput
improvement between
  single-threaded and setting the thread count to 2, for a single
forward FFT of size 2**19.

The implementation allows you to set variables in the [fftw] section of
the prefs file as follows:

[fftw]
nthreads=1
threshold=15000
measure=False

nthreads:  maximum number of threads that the FFTW3F scheduler will use
threshold: the minimum FFT size before we turn on multi-threaded FFTW
scheduling
measure:  whether the FFT setup uses FFTW_MEASURE or FFTW_ESTIMATE

More tests in my lab tomorrow, on my 6-core Phenom II system.


--
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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