First commit of OpenMP documentation.

docs/software/nodelevel_parallelism/index.md

@@ -0,0 +1,6 @@
+[](){#ref-software-nodelevel-parallelism}
+# Node-Level Parallelism Libraries
+
+See the individual pages for each library for information on how to use and best configure the libraries.
+
+* [OpenMP][openmp]

docs/software/nodelevel_parallelism/openmp.md

@@ -0,0 +1,23 @@
+[](){#openmpi}
+# OpenMP
+
+[OpenMP](https://www.openmp.org/specifications/) OpenMP is a shared-memory parallel programming API that provides compiler directives, runtime routines, and environment variables to simplify multithreading in C, C++, and Fortran.
+It is a common library that HPC applications use to achieve node-level parallelism.
+
+
+## Known issues
+
+!!! warning
+    As of 26-Mar-2025 the [Santis][ref-cluster-santis] cluster is configured in "Low Noise Mode" (LNM). This setting confines system processes and operations
+    to the first core of each of the four NUMA regions in a node (i.e., cores 0, 72, 144, 216).
+
+    The consequence of this setting is that only 71 cores per socket can be requested by an application (for a total of 284 cores instead of 288 cores per node).
+
+    Furthermore, LNM requires that OpenMP-based applications instruct OpenMP to properly place threads on the remaining cores.
+
+On [Santis][ref-cluster-santis] the recommended OpenMP affinity settings are
+
+```bash
+export OPENMP_PLACES=cores
+export OPENMP_PROC_BIND=close
+```

mkdocs.yml

@@ -64,6 +64,9 @@ nav:
       - 'NCCL': software/communication/nccl.md
       - 'RCCL': software/communication/rccl.md
       - 'libfabric': software/communication/libfabric.md
+    - 'Node-level Parallelism Libraries':
+      - software/nodelevel_parallelism/index.md
+      - 'OpenMP': software/nodelevel_parallelism/openmp.md
     - 'Building and Installing software':
       - build-install/index.md
       - 'uenv': build-install/uenv.md