Parallelism on CRAY Multiprocessor Systems: Concepts of Multitasking

Modern supercomputers like CRAY X-MP and CRAY Y-MP achieve their high computing speed by using both vector and parallel hardware. This paper gives a short introduction into the CRAY Y-MP system architecture and describes the multitasking concepts which can be used on this machine. There are three different concepts which support parallelism on the programming language level: macrotasking, microtasking, and autotasking. The concepts and implementations are discussed, and measurements of the overhead as well as performance results for kernels and an application program are presented.Moreover, the overall system performance is of interest when multitasking concepts are used. Therefore, a programming system is developed, generating synthetic user programs which simulate a given work load in a flexible way. The resulting benchmark environment is used to insert additional sequential as well as parallel programs. This technique guarantees constant system load and enables reasonable comparisons. First results obtained from these investigations have proved the efficiency especially for the fine-grain concepts which provide good performance in dedicated as well as batch oriented multiprogramming environments