Comment (by Roland Haas):

This ticket has been around for a while. I would still think that since OpenBLAS is x86 specific and even on x86 machines fails to compile if the processor is too new (or old I guess), I would not want it to be the default.

Instead clusters where indeed we could compile BLAS and LAPACK libs from scratch can use simfactory’s enabled-thorns and disable-thorns options to enable OpenBLAS. If we do not compile, which is the usual case on clusters, then there is no difference between using BLAS/LAPACK externallibraries and OpenBLAS.

That leaves the case of user workstations and unknown clusters. On a user workstation, with automated setup, speed should not matter so I would strongly advocate to use the “compiles everywhere” BLAS and LAPACK even if they are slow. In particular since the ET as a whole doe not depend on those for speed.

On clusters, speed does matter, but setting up on a cluster requires some expertise anyway and we should be able to expect that those doing so will be able to set the correct LAPACK_DIR and BLAS_DIR variables to point to the system installed good BLAS / LAPACK library. If there are indeed HPC clusters where those libraries are not provide, then those clusters may be best avoided.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/1674/switch-to-openblas