HP-MPI User's Guide (11th Edition)

Tuning
Coding considerations
Chapter 5 193
Coding considerations
The following are suggestions and items to consider when coding your
MPI applications to improve performance:
• Use HP-MPI collective routines instead of coding your own with
point-to-point routines because HP-MPI’s collective routines are
optimized to use shared memory where possible for performance.
Use commutative MPI reduction operations.
— Use the MPI predefined reduction operations whenever possible
because they are optimized.
— When defining your own reduction operations, make them
commutative. Commutative operations give MPI more options
when ordering operations allowing it to select an order that leads
to best performance.
• Use MPI derived datatypes when you exchange several small size
messages that have no dependencies.
• Minimize your use of MPI_Test() polling schemes to reduce polling
overhead.
• Code your applications to avoid unnecessary synchronization. In
particular, strive to avoid MPI_Barrier calls. Typically an application
can be modified to achieve the same end result using targeted
synchronization instead of collective calls. For example, in many
cases a token-passing ring may be used to achieve the same
coordination as a loop of barrier calls.