Hiding Memory Latency using Dynamic Scheduling in Shared-Memory Multiprocessors

Abstract

The large latency of memory accesses is a major impediment to achieving high performance in large scale shared-memory multi- processors. Relaxing the memory consistency model is an attractive technique for hiding this latency by allowing the overlap of memory accesses with other computation and memory accesses. Previous studies on relaxed models have shown that the latency of write accesses can be hidden by buffering writes and allowing reads to bypass pending writes. Hiding the latency of reads by exploiting the overlap allowed by relaxed models is inherently more difficult, however, simply because the processor depends on the return value for its future computation. This paper explores the use of dynamically scheduled processors to exploit the overlap allowed by relaxed models for hiding the latency of reads. Our results are based on detailed simulation studies of several parallel applications. The results show that a substantial fraction of the read latency can be hidden using this technique. However, the major improvements in performance are achieved only at large instruction window sizes.