open TELEMAC-MASCARET The mathematically superior suite of solvers

Q: What are process managers?

A: Process managers are basically external (typically distributed) agents that spawn and manage parallel jobs. These process managers communicate with MPICH processes using a predefined interface called as PMI (process management interface). Since the interface is (informally) standardized within MPICH and its derivatives, you can use any process manager from MPICH or its derivatives with any MPI application built with MPICH or any of its derivatives, as long as they follow the same wire protocol. There are three known implementations of the PMI wire protocol: "simple", "smpd" and "slurm". By default, MPICH and all its derivatives use the "simple" PMI wire protocol, but MPICH can be configured to use "smpd" or "slurm" as well.

For example, MPICH provides several different process managers such as Hydra, MPD, Gforker and Remshell which follow the "simple" PMI wire protocol. MVAPICH2 provides a different process manager called "mpirun" that also follows the same wire protocol. OSC mpiexec follows the same wire protocol as well. You can mix and match an application built with any MPICH derivative with any process manager. For example, an application built with Intel MPI can run with OSC mpiexec or MVAPICH2's mpirun or MPICH's Gforker.

MPD has been the traditional default process manager for MPICH till the 1.2.x release series. Starting the 1.3.x series, Hydra is the default process manager.

SMPD is another process manager distributed with MPICH that uses the "smpd" PMI wire protocol. This is mainly used for running MPICH on Windows or a combination of UNIX and Windows machines. This will be deprecated in the future releases of MPICH in favour or Hydra