Prevent OpenMPI from failing on machines with less than 8 cores

[schiotz]

Possible fix for issue easybuilders/easybuild-easyconfigs#13945 (comment)

It needs testing, and it might cause problems on machines with two cores and no hyperthreading.

[boegel]

Hmm, I think we need to come up with a better way of fixing this...

The hardcoded 8 here is the problem really, isn't it?

[ocaisa]

Isn't the simplest fix to just allow oversubscription?

[schiotz]

Yes, the hardcoded 8 is the problem. And allowing oversubscription is probably the simplest and cleanest solution.

[schiotz]

Should we just close this PR, now that @ocaisa has come up with a superior solution (#2611)?

[boegel]

Strangely enough I've also run into this on a system with 64 cores (AWS Graviton2 instance c6gd.16xlarge)...

I worked around it using export OMPI_MCA_rmaps_base_oversubscribe=1 followed by eb --module-only (but we should go ahead with the fix proposed in #2611, unless we want to set $OMPI_MCA_rmaps_base_oversubscribe more broadly in the sanity check via EasyBuild framework when OpenMPI is used as toolchain component, since this also applies to OpenFOAM, see #2615).

[boegel]

Closing this in favor of #2611, simply allowing oversubscription is a better/broader fix imho...