HP-MPI provides a mix of command line options and environment variables
that can be used to influence the behavior, and thus the performance
of the library. The full list of command line options and environment
variables are presented in the sections ““mpirun
options”” and ““Runtime
environment variables”” of Chapter 3. The options
and variables of interest to performance tuning include the following:
MPI_FLAGS=y |
 |
This option can be used to control
the behavior of the HP-MPI library when waiting for an event to
occur, such as the arrival of a message. See “MPI_FLAGS” for more information.
MPI_TCP_CORECVLIMIT |
|
Setting this variable to a larger value can allow HP-MPI to
utilize more parallelism during its low-level message transfers,
but can greatly reduce performance by causing switch congestion.
See “MPI_TCP_CORECVLIMIT” for more
information.
MPI_SOCKBUFSIZE |
|
Increasing this value has shown performance gains for some
applications running on TCP networks. See “MPI_SOCKBUFSIZE” for more information.
-intra |
|
The -intra command line option controls how
messages are transferred to local processes and can impact performance
when multiple ranks execute on a host. See “Local
host communication method” for more information.
MPI_RDMA_INTRALEN, MPI_RDMA_MSGSIZE, MPI_RDMA_NENVELOPE |
|
These environment variables control various aspects of the
way message traffic is handled on RDMA networks. The default settings
have been carefully selected to be appropriate for the majority
of applications. However, some applications may benefit from adjusting
these values depending on their communication patterns. See the
corresponding man pages for more information.
MPI_USE_LIBELAN_SUB |
|
Setting this environment variable may provide some performance benefits
on the ELAN interconnect. However, some applications may experience
resource problems. See “MPI_USE_LIBELAN_SUB” for more information.
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