Performance of the Message Passing Libraries
- Latency is the time it takes to pass a very short (zero length) message
- Bandwidth is the sustained performance passing long messages
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- the “single” test is using the send/recv pair; “multiple” test uses the equivalent of the sendrecv primitive
- Note that a single bcopy speed on Origin2000 is about 150 MB/s
- MPI suffers a performance disadvantage with respect to SHMEM due to the fact that MPI semantics requires separate address spaces between threads. Therefore MPI implementation requires “double copy” to pass messages.
- SHMEM is optimized for one-sided communication as is done for SMP programming and therefore shows a very good latency measurement.