Merge pull request #11746 from hppritcha/slurm_srun_doc_update

docs: update verbiage for using srun

Author: hppritcha

docs/launching-apps/slurm.rst

@@ -61,41 +61,42 @@ that information directly from Slurm at run time.
 Using Slurm's "direct launch" functionality
 -------------------------------------------
 
-Assuming that Slurm installed its Open MPI plugin, you can use
+Assuming that Slurm was configured with its PMIx plugin, you can use
 ``srun`` to "direct launch" Open MPI applications without the use of
 Open MPI's ``mpirun`` command.
 
-.. note:: Using direct launch can be *slightly* faster when launching
-   very, very large MPI processes (i.e., thousands or millions of MPI
-   processes in a single job).  But it has significantly fewer
-   features than Open MPI's ``mpirun``.
+First, you must ensure that Slurm was built and installed with PMIx
+support.  This can determined as shown below:
 
-First, you must ensure that Slurm was built and installed with PMI-2
-support.
+.. code-block:: sh
+
+   shell$ srun --mpi=list
+   MPI plugin types are...
+	none
+	pmi2
+	pmix
+   specific pmix plugin versions available: pmix_v4
 
-.. note:: Please ask your friendly neighborhood Slurm developer to
-          support PMIx.  PMIx is the current generation of run-time
-          support API; PMI-2 is the legacy / antiquated API.  Open MPI
-          *only* supports PMI-2 for Slurm.
+The output from ``srun`` may vary somewhat depending on the version of Slurm installed.
+If PMIx is not present in the output, then you will not be able to use srun
+to launch Open MPI applications.
 
-Next, ensure that Open MPI was configured ``--with-pmi=DIR``, where
-``DIR`` is the path to the directory where Slurm's ``pmi2.h`` is
-located.
+.. note:: PMI-2 is not supported in Open MPI 5.0.0 and later releases.
 
-Open MPI applications can then be launched directly via the ``srun``
-command.  For example:
+Provided the Slurm installation includes the PMIx plugin, Open MPI applications 
+can then be launched directly via the ``srun`` command.  For example:
 
 .. code-block:: sh
 
-   shell$ srun -N 4 mpi-hello-world
+   shell$ srun -N 4 --mpi=pmix mpi-hello-world
 
 Or you can use ``sbatch`` with a script:
 
 .. code-block:: sh
 
    shell$ cat my_script.sh
    #!/bin/sh
-   srun mpi-hello-world
+   srun --mpi=pmix mpi-hello-world
    shell$ sbatch -N 4 my_script.sh
    srun: jobid 1235 submitted
    shell$