Re: question on parallel processing

[Joshua Rigler]

Jurzitza, Dieter wrote:
> Dear listmembers, is there any way for octave to do a parallel
> processing (i. e. when multiplying matrices, start 4 lines processing
> in parallel on 4 cpus), and if so, is there a pointer to a RTFM some
> kind person could point me to? Many thanks in advance, take care
>
>
> Dieter Jurzitza


Dieter,

In order to speed up certain matrix operations on shared memory 
multi-cpu systems, you can use ATLAS' posix threaded blas libraries 
(libptcblas.a, libptf77blas.a, and libatlas.a) instead of the default 
blas libraries.  You may be able to download these precompiled, or you 
might have to compile them yourself...this email won't cover that 
process, which can be a bit tedious if you have a non-standard system.

If that all goes smoothly (BIG "if"), you should have threaded blas 
libraries for both C and F77.  My notes are old, but they seem to agree 
with the config.log file I found in my old Octave source code directory. 
 My configure invocation appears to have been (should be all on one line):

  ./configure --enable-shared --enable-dl --enable-lite-kernel 
--with-blas=-lptcblas -lptf77blas -latlas -lpthread 
--with-lapack=/usr/local/lib/liblapack.a

You'll note that I had to link explicitly to my own lapack library too. 
 This was because I forced the "-fPic" option when compiling lapack.a 
in order to make it compatible with posix threads and the ATLAS 
libraries.  Fedora, at the time, was compiling lapack with the "-fnoPic" 
option by default.  Note also that this all assumes that your shiny new 
threaded blas libraries are already in the dynamic linker's default 
path, or you must append "LDFLAGS=-L/path/to/libs" to the command above. 
 You might also be required to append "CPPFLAGS=-I/path/to/headers" so 
the compiler can find the necessary .h files.

Keep in mind that I did all of this well over a year ago, when the 2.9 
snapshots were only a gleam in JWE's eyes.  FWIW, I have since migrated 
to using the latest Octave and Octave-Forge packages available through 
Fedora Extras, which are NOT compiled to link to parallel blas libraries 
as far as I know.  The hassle of recompiling everything every time a new 
version came out outweighed the improvements in performance I saw for 
only a handful of Octave matrix operations.  I'd say that unless you 
have something you want to put into a production environment, it's not 
really worth all the trouble.

-EJR