In this paper, we present an architecture-compiler based approach to reduce energy consumption in the processor. While we mainly target the fetch unit, an important side-effect of our approach is that we obtain energy savings in many other parts in the processor. The explanation is that the fetch unit often runs substantially ahead of execution, bringing in instructions to different stages in the processor that may never be executed. We have found, that although the degree of Instruction Level Parallelism (ILP) of a program tends to vary over time, it can be statically predicted by the compiler with considerable accuracy. Our Instructions Per Clock (IPC) prediction scheme is using a dependence-testing-based analysis and simple heuristics, to guide a front-end fetch-throttling mechanism. We develop the necessary architecture support and include its power overhead. We perform experiments over a wide number of architectural configurations, using SPEC2000 applications.
our results are very encouraging: we obtain up to 15% total energy savings in the processor with generally little performance degradation. In fact, in some cases our intelligent throttling scheme even increases performance.