User guide

A–Benchmark Programs
Benchmark 1: Measuring MPI Latency Between Two Nodes
A-2 IB0054606-02 A
The program osu_latency, from Ohio State University, measures the latency for
a range of messages sizes from 0bytes to 4 megabytes. It uses a ping-pong
method, where the rank zero process initiates a series of sends and the rank one
process echoes them back, using the blocking MPI send and receive calls for all
operations. Half the time interval observed by the rank zero process for each
exchange is a measure of the latency for messages of that size, as previously
defined. The program uses a loop, executing many such exchanges for each
message size, to get an average. The program defers the timing until the
message has been sent and received a number of times, to be sure that all the
caches in the pipeline have been filled.
This benchmark always involves two node programs. It can be run with the
command:
$ mpirun -H host1,host2 \
/usr/mpi/gcc/openmpi-1.4.3-qlc/tests/osu_benchmarks-3.1.1/osu
_latency