QLogic OFED+ Host Software User Guide, Rev. B

B–Benchmark Programs
Benchmark 1: Measuring MPI Latency Between Two Nodes
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 osu_latency
-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 (Version 2.0)
# Size Latency (us)
0 1.06
1 1.06
2 1.06
4 1.05
8 1.05
16 1.30
32 1.33
64 1.30
128 1.36
256 1.51
512 1.84
1024 2.47
2048 3.79
4096 4.99
8192 7.28
16384 11.75
32768 20.57
65536 58.28
131072 98.59
262144 164.68
524288 299.08
1048576 567.60
2097152 1104.50
4194304 2178.66
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 TrueScale installation.
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