OpenMPI does not build on machine with six cores

[schiotz]

Hi,

Building OpenMPI/4.0.5-GCC-10.2.0 fails on a desktop with 6 cores and hyperthreading, because the sanity check attempts to run with 8 tasks, and mpiexec refuses to run with more tasks than there are physical cpus. The error is "Not enough slots to satisfy the 8 slots that were requested."

Maybe the test suite should be run with an option to allow oversubscribing the cpu cores?

CC: @matthewhelmi

[branfosj]

I think building with --parallel 6 will solve this issue.

More generally, we may want to reduce the 8 at https://github.com/easybuilders/easybuild-easyblocks/blob/develop/easybuild/easyblocks/o/openmpi.py#L182 to be 6 (or 4).

[schiotz]

I think building with --parallel 6 will solve this issue.

More generally, we may want to reduce the 8 at https://github.com/easybuilders/easybuild-easyblocks/blob/develop/easybuild/easyblocks/o/openmpi.py#L182 to be 6 (or 4).

Or maybe this: easybuilders/easybuild-easyblocks#2570
where we try not to use more than half the cores, assuming that hyperthreading amplifies the number of cores by a factor 2.

[boegel]

This should be fixed now, thanks to the tweak in the OpenMPI easyblock that was implemented in easybuilders/easybuild-easyblocks#2611...