User guide

A–Benchmark Programs
Benchmark 1: Measuring MPI Latency Between Two Nodes
IB0054606-02 A A-3
-H (or --hosts) allows the specification of the host list on the command line
instead of using a host file (with the -m or -machinefile option). Since only two
hosts are listed, this implies that two host programs will be started (as if -np 2
were specified). The output of the program looks like:
# OSU MPI Latency Test v3.1.1)
# Size Latency (us)
0 1.67
1 1.68
2 1.69
4 1.68
8 1.68
16 1.93
32 1.92
64 1.92
128 1.99
256 2.12
512 2.38
1024 2.74
2048 3.52
4096 4.59
8192 6.52
16384 9.98
32768 17.65
65536 52.11
131072 84.07
262144 114.90
524288 241.97
1048576 422.41
2097152 783.21
4194304 1596.37
The first column displays the message size in bytes. The second column displays
the average (one-way) latency in microseconds. This example shows the syntax
of the command and the format of the output, and is not meant to represent actual
values that might be obtained on any particular IB installation.