Hi Martin, @ports,
Here is a proposed README for the OpenMPI port.
John
--- /dev/null Fri Jan 24 18:21:22 2020
+++ pkg/README Fri Jan 24 01:02:54 2020
@@ -0,0 +1,30 @@
+
++-----------------------------------------------------------------------
+| Customizing ${PKGSTEM} execution on OpenBSD
++-----------------------------------------------------------------------
+
+The OpenMPI runtime is controlled by numerous values specified
+on the command line or with environment variables. See mpirun(1) and
+ompi_info(1). Example:
+
+ $ export PMIX_MCA_gds=hash
+ $ mpirun -np 2 -H localhost:2 \
+ -mca btl tcp,self \
+ -mca mpi_yield_when_idle 1 -- \
+ ./foo
+
+These values (at least) are useful:
+
+ OMPI_MCA_btl=self,tcp,vader
+ Avoid "vader" when launching many processes per node
+ and you have an NFS swap file. Or use local backing store.
+ (BTL is byte transfer layer. "vader" is shared memory
+ communication module.)
+
+ OMPI_MCA_mpi_yield_when_idle=1
+ Set to 1 may improve throughput when launching many
+ processes per node.
+
+ PMIX_MCA_gds=hash
+ This is the one gds (general data service) that works on OpenBSD.
+
