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A – Benchmark Programs

Benchmark 4: Measuring MPI Latency in Host Rings

IB6054601-00 D A-5

A.4

Benchmark 4: Measuring MPI Latency in Host Rings

The program mpi_latency can be used to measure latency in a ring of hosts. Its

syntax is a bit different from Benchmark 1 in that it takes command line arguments

that let you specify the message size and the number of messages over which to

average the results. So, for example, if you have a hosts file listing four or more

nodes, the command:

$ mpirun -np 4 -ppn 1 -m mpihosts mpi_latency 100 0

might produce output like this:

0 1.760125

This indicates that it took an average of 1.76 microseconds per hop to send a

zero-length message from the first host, to the second, to the third, to the fourth,

and then get replies back in the other direction.

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