Measurement of memory access contentions in multiple vector processor systems
Ingrid Y. Bucher, Margaret L. Simmons · 1991
Delays caused by memory access conjiicts were measured for vector operations on the CRAY Y-MP and CRAY X-MP, and on two versions of the CRAY-2 with static and dynamic memory.The delays were measured as jimctions of vector length and the number of active processors.The observed delays were lowest for memory access operations with stride one.Considerably higher delays were observed for mixed strides or random access.For access operations with mixed strides, measurements indicate that memory access was slowed down by a factor of up to 1.7 for the 8-processor CRAY Y-MP.For the 4processor machines, the factors were 3.1 for the CRAY X-MP, 4.4 for the CRAY-2 with dynamic memory, and 2.5 for the CRAY-2 with static memory.The results are compared with a queueing model of memory bank conjiicts.A model of vector performance with vector loop unrolling is presented as a special case of a previously published model.