Using multiple CPUs for problem solving: Experiences in multitasking on the CRAY X-MP/48

The integration of vector computers into multiprocessor configurations allows the use of multiple high-speed processors in parallel for one program. There are two aspects which are considered to be important for an efficient use of multiprocessor configurations. First, the flexibility, speed and user friendliness of the available synchronization and communication primitives, and second, the user problems in detecting data dependencies and in translating programs correctly into the parallel form required by the system. This paper is intended to give an overview of our experiences in multitasking using up to four CPUs of a CRAY X-MP/48. The results gained by macrotasking and microtasking will be compared for program kernels and real-life application programs. Special attention is paid to the difficulties of using more than two CPUs in parallel.