Usability.

MPI is well-integrated with the PE/POE infrastructure. This infrastructure provides, among other things:

• Parallel job startup, including optional automatic space sharing of parallel applications.
• Signal propagation to all processes in a parallel application.
• Flexible handling of standard I/O: standard output may be labeled by processor number and/or ordered by processor number; standard input may be broadcast to all processes or sent to a single process.
• An integrated batch queuing system called Loadleveler.

Unfortunately there remain a number of usability problems related to PE/POE. Though not problems with the MPI implementation itself, these interfere with the usability of MPI. For example:

• Numerous user-settable options for poe do not have reasonable defaults.
• Signal propagation is not entirely foolproof, so that orphaned processes are not uncommon
• Parallel jobs are still second-class citizens. For example, there is no good way to see what parallel jobs are running on the system. The standard utility, jm_status, produces verbose output that is not easily parsed by humans.
• Despite improvement since earlier releases, the batch system Loadleveler requires substantial local customization and tools to be useful.