Minimum external Libevent version for Open MPI 5.0?

[bwbarrett]

With Open MPI 5.0, we are trying to be much more aggressive about using external libevent (and hwloc) packaging, rather than our internal packages. Currently, we prefer the internal version if the external version is older than the internal version (2.0.22). We are trying to find the oldest version Open MPI supports to prefer external in those cases. For testing purposes, we start with the distro versions:

Distribution	Libevent version
Amazon Linux 1	2.0.21
Amazon Linux 2	2.0.21
RHEL 6.10	2.0.21
RHEL 7.7	2.0.21
RHEL 8.0	2.1.8
SLES 12 sp5	2.0.5
SLES 15 sp1	2.1.8
Ubuntu 16.04	2.0.5
Ubuntu 18.04	2.1.8
Ubuntu 20.04	2.1.7

Or, sorted by Libevent version:

Libevent version	Shipping Distros
2.0.5	SLES 12 sp5, Ubuntu 16.04
2.0.21	Amazon Linux 1, Amazon Linux 2, RHEL 6.10, RHEL 7.7
2.1.7	Ubuntu 20.04
2.1.8	RHEL 8.0, SLES 15sp1, Ubuntu 18.04

We know based on informal testing that Libevent 2.0.21 works with Open MPI. We have not tested back to 2.0.5. Ubuntu 16.04 EOLs in April 2021 and SLES 12 EOLs in October 2024.

[bwbarrett]

Copied this data to https://github.com/open-mpi/ompi/wiki/OMPI-Third-Party-Packages

Also, on the call yesterday, we decided to set the minimum version to default to external support to 2.0.21, based on this data.