Which parallel communication pattern is used in the random and natural ring benchmark?
For measuring latency and bandwidth of parallel communication, all processes are arranged in a ring topology and each process sends and receives a message from its left and its right neighbor in parallel. Two types of rings are reported: a naturally ordered ring (i.e., ordered by the process ranks in MPI_COMM_WORLD), and the geometric mean of ten different randomly chosen process orderings in the ring. The communication is implemented (a) with MPI standard non-blocking receive and send, and (b) with two calls to MPI_Sendrecv for both directions in the ring. Always the fastest of both measurements are used. For benchmarking latency and bandwidth, 8 byte and 2,000,000 byte long messages are used. With this type of parallel communication, the bandwidth per process is defined as total amount of message data divided by the number of processes and the maximal time needed in all processes. This part of the benchmark is based on patterns studied in the effective bandwidth communication benchma
