In this program increasing sized messages are sent back and forth between processes - this is commonly called PingPong. This benchmark is based on standard blocking MPI_Send/MPI_Recv. PingPong provides information about latency of MPI_Send/MPI_Recv and uni-directional bandwidth. To ensure that anomalies in message timings are minimised the PingPong is repeated many times for each message size. The codes used for these tests were those developed by Baker and Grassl. The three existing codes (MPI-C, MPI-Fortran and Winsock-C) were used for comparison and we implemented an mpiJava version for our purposes.
The main problem encountered running the PingPong code was that under WMPI on Win32 MPI_Wtime() had been implemented with a millisecond resolution. It was necessary to adapt each of the codes to use an alternative timer with microsecond (s) resolution. The performance tests shown in the next section were run on two similar systems:
Both systems were connected via 10BaseT Ethernet and the tests were carried out when there was little network activity and on quiet machines.