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Re: 2.9.6 build fails on an Opteron RHEL4

From: Javier Fernández Baldomero
Subject: Re: 2.9.6 build fails on an Opteron RHEL4
Date: Wed, 14 Jun 2006 12:01:36 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)

| I use K. Goto's BLAS (and a LAPACK compiled against  the GOTO BLAS lib).

So, is it compiled in a way that ensures that the integer quantities
are 8 byte signed integers?

I am supervising a class assignment comparing Octave performance with and without ATLAS and Goto's BLAS. There were/are lots of things I was not aware of. For instance, ATLAS includes a BLAS _and_ a LAPACK. The student found a nice benchmark from, more detailed (and adaptable to Octave) than the one available from Mathworks' File Exchange.

There is some weird result that GotoBlas + LAPACK is worse than GotoBLAS alone. A previous weirdness that GotoBLAS wasn't better than ATLAS BLAS was due to not using LD_PRELOAD before running Octave. I was suggesting LD_LIBRARY_PATH to the student, without any results. Thanks to David for his e-mail from 2003.
I would have suggested that same benchmark to the student if I had remembered that e-mail earlier.

I'm not sure why the LD_LIBRARY_PATH didn't make the trick. In fact, right now I'm a bit messed up with shared libraries concepts. The symbols defined in the GotoBLAS library are not exactly the same as in ATLAS BLAS (there are underscore_letter variants). Anyways, from reading this thread I deduce I should instruct the student to link his ATLAS LAPACK against the improved GotoBLAS, isn't it? How would he do it? Does it really depend on link-time flags? Or does it depend on which library is loaded at run-time?

In other words: as long as you build your libraries as shared objects, it really doesn't matter which one you compile Octave against. It only matters which one is found at load/runtime. Is that true? If so, it doesn't matter either, which BLAS do you link LAPACK against. It only matters which BLAS is preloaded when you load LAPACK (ok, when Octave loads it).

If LAPACK depends on BLAS, precisely on ATLAS BLAS, that could be the explanation for the weird student result that GotoBLAS+LAPACK is worse than GotoBLAS alone (if loading ATLAS LAPACK overrides the GotoBLAS preload). Is there any good reference on these issues? Is there any other likely explanation?

Thanks for any help, sincerely confused :-)


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