Abstract. One-sided Communications is one of the extensions to MPI set out in the MPI-2 standard. We present here a thread-based implementation of One-sided Communications written for WMPI, an existing Windows implementation of MPI written at the Universidade de Coimbra. This is a major step towards WMPI incorporating the MPI-2 standard, with the further bene t of contributing to the thread safety of WMPI. We discuss the main design decisions associated with the implementation and consider further research work required in this area to improve both the existing implementation and to assess other implementations of One-sided Communications. 1

. Since MPI [1] has become a standard for message-passing on distributed memory machines a number of implementations have evolved. Today there is an MPI implementation available for all relevant MPP systems, a number of which is based on MPICH [2]. In this paper we are going to present performance comparison for several implementations of MPI on different MPPs. Results for the Cray T3E, the IBM RS/6000 SP, the Hitachi SR2201 and the Intel Paragon are presented. In addition we compare those results to the NEC SX-4, a shared memory PVP. Results presented will show latency and bandwidth for point-to-point communication. In addition results for global communications and synchronization will be given. This covers a wide range of MPI features used by typical numerical simulation codes. Finally we investigate a core conjugate gradient solver operation to show the behaviour of latency-hiding techniques on different platforms. 1 Introduction Since MPI has become the standard for message-passin...

this paper. Furthermore all measurements presented here were done with warm-up of the network