Parallel Programming Guide for HP-UX Systems

MPI
Running
Chapter 2 33
amount
where amount specifies the total amount of shared memory in bytes for all processes. The
default is 2 Mbytes for up to 64-way applications and
4 Mbytes for larger applications.
Be sure that the value specified for MPI_GLOBMEMSIZE is less than the amount of global shared
memory allocated for the host. Otherwise, swapping overhead will degrade application
performance.
MPI_INSTR MPI_INSTR enables counter instrumentation for profiling HP MPI applications.
The MPI_INSTR syntax is a colon-separated list (no spaces between options) as follows:
prefix [...]][:l][:nc][:off]
where
prefix Specifies the instrumentation output file prefix. The rank zero process
writes the application’s measurement data to prefix .instr in ASCII. If the
prefix does not represent an absolute pathname, the instrumentation output
file is opened in the working directory of the rank zero process when
MPI_Init is called.
l Locks ranks to cpus and uses the cpu’s cycle counter for less invasive timing.
If used with gang scheduling, the :l is ignored.
nc Specifies no clobber. If the instrumentation output file exists, MPI_Init
aborts.
off Specifies counter instrumentation is initially turned off and only begins
after all processes collectively call MPIHP_Trace_on.
Even though you can specify profiling options through the MPI_INSTR environment variable,
the recommended approach is to use the mpirun command with the -i option instead. Using
mpirun to specify profiling options guarantees that multihost applications do profiling in a
consistent manner. Refer to “mpirun (mpirun.all)” on page 36 for more information.
Counter instrumentation and trace-file generation are mutually exclusive profiling
techniques.
NOTE When you enable instrumentation for multihost runs, and invoke mpirun either
on a host where at least one MPI process is running, or on a host remote from
all your MPI processes, HP MPI writes the instrumentation output file
( prefix .instr) to the working directory on the host that is running rank 0.