Summary

Most HPC systems are clusters of shared memory nodes. Parallel programming must combine the distributed mem-ory parallelization on the node inter-connect with the shared memory parallelization inside of each node. Various hybrid MPI+OpenMP programming models are compared with pure MPI. Benchmark results of several platforms are presented. This paper analyzes the strength and weakness of several parallel programming models on clusters of SMP nodes. Benchmark results on a Myrinet cluster and on re-cent Cray, NEC, IBM, Hitachi, SUN and SGI platforms show, that the hybrid-masteronly programming model can be used more eciently on some vector-type systems, but also on clusters of dual-CPUs. On other systems, one CPU is not able to saturate the inter-node network and the commonly used masteronly programming model suers from insucient inter-node bandwidth. This paper analy-ses strategies to overcome typical drawbacks of this easily usable programming scheme on systems with weaker inter-connects. Best performance can be achieved with overlap-ping communication and computation, but this scheme is lacking in ease of use