Abstract—Programs that execute in parallel across a network often use the Message Passing Interface (MPI) library for communication. The network requirements of an MPI program are often unclear because of the difficultyin exploring alternative network configurations as well as obtaining packet level information about the communication. MPI-NeTSim is an execution environment to emulate MPI programs on simulated networks to allow users to better explore the impact of the network on the performance of MPI programs. We describe the design of MPI-NeTSim and the integration of OMNeT++’s INET framework into MPICH2’s MPI middleware. We introduce a novel technique for uniformly slowing down the execution of the system to allow the discrete event network simulator to keep up with the execution and provide a consistent view of the communication. We validate our technique with synthetic programs as well as the standard NAS benchmarks. We demonstrate MPI-NeTSim’s usefulness in analyzing the effect of the network on communication by using our environment to study the impact of a slow-link on the NAS benchmarks. I
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