[SciPy-dev] Absoft & Scipy

Stephen Walton stephen.walton at csun.edu
Fri Feb 4 12:51:40 CST 2005

Stephen Walton wrote:

> I wonder how much performance I really gain by insisting on compiling 
> with Absoft.  Off to run some benchmarks...

Well, I have some answers.  I ran "make blaslib" followed by "make 
timing" in the LAPACK source directory.  Note that this means I'm using 
the reference Fortran BLAS and not the tuned ATLAS one.

Almost all the results of "make timing" show that g77/gcc is faster than 
Absoft on most of the benchmarks, often substantially.  For example 
(this is random), a 40 by 40 array fed to SGEBRD hits 458 MFlops on 
Absoft and 629 with g77.  This is with -O3 on both compilers on a P4SSE2 
2.2GHz system.  The only exceptions are some of the double complex 
computations, where Absoft has a small edge for some routine/problem 
size combinations.

I tried the Intel compiler as well (free noncommercial download of 
version 8.1.).  The testslamch program in LAPACK goes into an infinite 
loop when compiled with this compiler...as does at least one of the 

In my own defense, we bought Absoft not for performance, though that was 
a consideration, but because we needed a Fortran 90/95 compiler.  g95 is 
Not Ready for Prime Time;  I just tried one of my primary codes with 
g95.  It ran but gave the wrong answer.

Bottom line:  unless you have a really hot optimizing compiler (and I'd 
like to know if you do) build LAPACK, ATLAS, and Scipy with g77.

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