Multiprocessor Cache Analysis

In recent times multiprocessing has become a popular means of achieving performance levels that can far exceed those of single processors. The design of high-performance multiprocessors necessitates a careful analysis of the memory system performance of parallel programs. The common theme of this section is the increased understanding of the dynamics of large writeback caches in multiple processors with shared memory. The multiprocessor extension of ATUM for gathering multiprocessor traces and its implementation on a VAX 8350 multiprocessor is first described. Because the resulting parallel traces are dissimilar to the traces used in our single processor studies, and since we would like isolate the effects of multiprocessing on cache performance from the effects of multiprogramming, we will first repeat some single processor experiments with the new traces, and compare the effect of cache interference between multiple processes in both physical-addressed and virtual-addressed caches. Such a study is possible with the extended ATUM scheme because a complete virtual to physical address map is contained in the traces. The performance degradation due to cache interference between multiple processors is then analyzed. The improvement in cache performance if process migration is disallowed is evaluated. We also study semaphore usage and its effect on cache performance.