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The empirical investigations revealed that our parallel implementation scales sufficiently well on Parix and PVM for moderate systems sizes (<256 processors). This is because few communication occurs in this specific application, and many requests are answered in the direct neighborship of the requester. For the larger system sizes, Parix clearly outperforms PVM. We expect the gap between Parix and PVM to become more pronounced in applications with a higher communication demand.
The performance loss for larger systems is mainly caused by the implementation of PVM for the transputer system. Especially the restriction that only one task on each processor is possible yields to slower communication because each message could not be processed immediately after receivement. Further it is not possible to do efficient work-load balancing if PVM does not provide any information about the MPP, i.e. the position of a task in the network or information about the tasks in the direct neighborship.