[petsc-users] prevent linking to multithreaded BLAS?

[Mark Lohry]

I ran into an unexpected issue -- on an NP-core machine, each MPI rank of
my application was launching NP threads, such that when running with
multiple ranks the machine was quickly oversubscribed and performance
tanked.

The root cause of this was petsc linking against the system-provided
library (libopenblas0-pthread in this case) set by the update-alternatives
in ubuntu. At some point this machine got updated to using the threaded
blas implementation instead of serial; not sure how, and I wouldn't have
noticed if I weren't running interactively.

Is there any mechanism in petsc or its build system to prevent linking
against an inappropriate BLAS, or do I need to be diligent about manually
setting the BLAS library in the configuration stage?

Thanks,
Mark
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