[gambit-list] New gcc and gambit

Bradley Lucier lucier at math.purdue.edu
Fri Apr 1 15:10:07 EDT 2011


I tried some preliminary tests of the newly released gcc-4.6.0 with
Gambit, and things look pretty good.

I was looking just at how long the routine direct-fft-recursive-4 in
lib/_num.scm took to execute on an array of $2^{25}$ complex doubles.
Here are various execution times comparing gcc-4.6.0 with the gcc-4.5.1
that ships with Ubuntu 10.10.  I just did "./configure CC=...; make" on
plain manilla gambit-4.6.0 with default optimization "-O1
-fschedule-insns2":

4.5.1:
    3180 ms cpu time (3160 user, 20 system)
4.6.0:
    2910 ms cpu time (2910 user, 0 system)

That's quite the improvement, nearly 10%

I also added -fschedule-insns to the optimization list:

4.5.1 -fschedule-insns:
    2870 ms cpu time (2870 user, 0 system)
4.6.0 -fschedule-insns:
    2730 ms cpu time (2730 user, 0 system)

Still about a 5% improvement.

Since there are 5 N \log_2 N operations in an FFT of size N, that last
time represents 1.536 Gflops on my 

model name	: Intel(R) Core(TM)2 Quad  CPU   Q8200  @ 2.33GHz

FFTW3 out-of-place (i.e, the same result, but not the same algorithm)
achieves almost exactly 2 Gflops on a 3.0 GHz machine with a better
memory system:

http://www.fftw.org/speed/CoreDuo-3.0GHz-icc64/

Scaling the results on my machine to the higher clock rate gives

> (* 1.56 3.0 (/ 2.33))
2.008583690987124

(I don't feel like benchmarking fftw3 on my own machine, sorry.)

So who says you can't do scientific computing in Scheme?

Brad

PS:  This is no April Fools joke!




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