Single instruction stream parallelism is greater than two

Abstract

Recent studies have concluded that little parallelism (less than two operations per cycle) is available in single instruction streams. Since the amount of available parallelism should influence the design of the processor, it is important to verify how much parallelism really exists. In this study we model the execution of the SPEC benchmarks under differing resource constraints. We repeat the work of the previous researchers, and show that under the hardware resource constraints they imposed, we get similar results. On the other hand, when all constraints are removed except those ~equired by the semantics oft he program, we have found degrees of parallelism in excess of 17 instructions per cycle. Finally, and perhaps most important for exploiting single instruction stream parallelism now, we show that if the hardware is properly balanced, one can sustain from 2.0 to 5.8 instructions per cycle on a processor that is reasonable to design today.