Data Forwarding in Scalable Shared-Memory Multiprocessors

Scalable shared-memory multiprocessors are often slowed down by long-latency memory accesses. One way to cope with this problem is to use data forwarding to overlap memory accesses with computation. With data forwarding, when a processor produces a datum, in addition to updating its cache, it sends a copy of the datum to the caches of the processors that the compiler identified as consumers of it. As a result, when the consumer processors access the datum, they find it in their caches. This paper addresses two main issues. First, it presents a framework for a compiler algorithm for forwarding. Second, using address traces, it evaluates the performance impact of different levels of support for forwarding. Our simulations of a 32-processor machine show that a slightlyoptimistic support for forwarding speeds up five applications by, on average, 50% for large caches and 30% for small caches. For large caches, many sharing read misses can be eliminated, while for smaller caches, forwarding ..