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From: ludovic.courtes@inria.fr (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: OpenBLAS and performance
Date: Thu, 21 Dec 2017 15:55:21 +0100
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In-Reply-To: <87tvwl7h4w.fsf@albion.it.manchester.ac.uk> (Dave Love's message
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To: Dave Love <fx@gnu.org>
Cc: Guix-devel <guix-devel@gnu.org>, Eric Bavier <bavier@cray.com>, Federico Beffa <beffa@ieee.org>

Hello,

Dave Love <fx@gnu.org> skribis:

> Fedora sensibly builds separately-named libraries for different flavours
> <https://apps.fedoraproject.org/packages/openblas/sources/>, but I'd
> argue also for threaded versions being available with the generic soname
> in librray sub-directories.  There's some discussion and measurements
> (apologies if I've referenced it before) at
> <https://loveshack.fedorapeople.org/blas-subversion.html>

I like the idea of an =E2=80=98update-alternative=E2=80=99 kind of approach=
 for
interchangeable implementations.

Unfortunately my understanding is that implementations aren=E2=80=99t entir=
ely
interchangeable, especially for LAPACK (not sure about BLAS), because
BLIS, OpenBLAS, etc. implement slightly different subsets of netlib
LAPACK, AIUI.  Packages also often check for specific implementations in
their configure/CMakeLists.txt rather than just for =E2=80=9CBLAS=E2=80=9D =
or =E2=80=9CLAPACK=E2=80=9D.

FlexiBLAS, which Eric mentioned, looks interesting because it=E2=80=99s des=
igned
specifically for that purpose.  Perhaps worth giving it a try.

Besides, it would be good to have a BLAS/LAPACK policy in Guix.  We
should at least agree (1) on default BLAS/LAPACK implementations, (2)
possibly on a naming scheme for variants based on a different
implementation.

For #1 we should probably favor implementations that support run-time
implementation selection such as OpenBLAS (or the coming BLIS release).

Thoughts?

Ludo=E2=80=99.