Editing Portal:HPC - High Performance Computing (section)

=== Hybrid MPI and OpenMP workflows ===

Modern HPC codes often combine programming models. A common pattern is '''MPI between nodes and OpenMP within each node'''. In this model, MPI distributes work across compute nodes, while OpenMP uses the cores within each node. This approach can reduce the number of MPI ranks, improve memory locality, and better match modern multi-core nodes.

Perl can support this hybrid model as the workflow layer. A Perl script can calculate how many nodes, ranks, threads, and memory should be requested; generate Slurm directives; set environment variables such as `OMP_NUM_THREADS`; launch the executable; and check whether the run behaved as expected.

For example, a Perl-driven HPC workflow might set:

* one MPI rank per NUMA domain;
* several OpenMP threads per rank;
* CPU binding options;
* memory limits;
* scratch directories;
* restart file paths;
* output validation checks.

This kind of practical automation is one of Perl’s strongest HPC roles.