[Neolith-users] mpprun update

[Mattias Slabanja]

To all Neolith test-users.

We have updated mpprun.

* There is a change in syntax for options to mpprun, see below,
or try mpprun --help at the command prompt on neolith.


General information about mpprun.

* It is an easy way to start your MPI-applications from within
   a SLURM environment. Because

- It automatically determines which MPI-implementation and version
   to use if the program is built according to the user guide.

- It automatically starts the application on the allocated resources.
   I.e. there is no need to manually calculate the number of MPI-ranks
   to start.

- It is seamless to pass options to the underlying MPI-launcher;
   every option entered after mpprun and before the binary,
   not recognized by mpprun, is passed on.

- If necessary, it is simple to explicitly choose any supported
   MPI-implementation, hence overriding any default behavior of
   mpprun. See info about the option --force-mpi=.



Examples:

To start an MPI-application called "hello-mpi", in a batch script, or 
from within an interactive shell, do

$ mpprun /example/path/hello-mpi
mpprun INFO: Number of tasks set to all cores on all allocated nodes (16).
mpprun INFO: Starting  run on 2 nodes...
Starting on rank 0 n9
Starting on rank 8 n10
Starting on rank 1 n9
...


To see available options, do

$ mpprun --help
Usage: mpprun [option] ... [option] <program> [options sent to program]

Arguments not recongnized as options to mpprun are passed to the
underlying MPI-launcher.
The first argument corresponding to an executable file, is assumed to
be the MPI-executable to be started.

Valid options to mpprun are the following:

--debug
         Probably only sysadmins would need this.
         To enable debug for mpprun, it must be stated as the _first_ 
argument.
         To be even more noisy, -NDEBUG can be used instead.

--force-mpi=<MPI module>
         Force the use of a selected MPI-module. MPI module must be
         given explicitly including version.
         Example: --force-mpi=scampi/3.12.0-1

--help
         This help.