How Useful Are Non-Blocking Loads, Stream Buffers and Speculative Execution in Multiple Issue Processors?

We investigate the relative performance impact of nonblocking loads, stream buffers, and specula five execution both used individually and in conjunction with each other. We have simulated the SPEC92 benchmarks on a statically scheduled quad-issue processor model. running code from the Multijlow compiler. Non-blocking loads and stream buffers both provide a signif cant performance advantage, and their combination performs significantly better than either alone. For example, with a 64-byte, 2-way set associative cache with 32 cycle fetch latency, non-blocking loads reduce the run-time by 21% while stream-buffers reduce it by 26%, and the combined use of the two yields a 47% reduction. The addition of speculative execution further improves the performance of the systems that we have simulated. with or without non-blocking loads and stream buffers, by an additional 20% to 40%. We expect that the use of all three of these techniques will be important in future generations of microprocessors.