# Intel MPI Support

This document describes which set of Intel MPI versions in PModules are supported in the Merlin6 cluster.

## Usage

### srun

We strongly recommend the use of **`srun`** over **`mpirun`** or **`mpiexec`**. Using **`srun`** would properly
bind tasks in to cores and less customization is needed, while **`mpirun`** and **`mpiexec`** might need more advanced
configuration and should be only used by advanced users. Please, ***always*** adapt your scripts for using **`srun`**
before opening a support ticket. Also, please contact us on any problem when using a module.

!!! tip
    Always run Intel MPI with the **srun** command. The only exception is
    for advanced users, however **srun** is still recommended.

When running with **srun**, one should tell Intel MPI to use the PMI libraries provided by Slurm. For PMI-1:

```bash
export I_MPI_PMI_LIBRARY=/usr/lib64/libpmi.so

srun ./app
```

Alternatively, one can use PMI-2, but then one needs to specify it as follows:

```bash
export I_MPI_PMI_LIBRARY=/usr/lib64/libpmi2.so
export I_MPI_PMI2=yes

srun ./app
```

For more information, please read [Slurm Intel MPI Guide](https://slurm.schedmd.com/mpi_guide.html#intel_mpi)

!!! note
    Please note that PMI2 might not work properly in some Intel MPI versions.
    If so, you can either fallback to PMI-1 or to contact the Merlin
    administrators.