On-demand solution to minimize I-cache leakage energy with maintaining performance

Abstract

This paper describes a new on-demand wake-up prediction policy for reducing leakage power. The key insight is that branch prediction can be used to selectively wake up only the needed cache line. This achieves better leakage savings than the best prior policies while avoiding the performance overheads of those policies, without needing an extra prediction structure. The proposed policy reduces leakage energy by 92.7 percent with only 0.08 percent performance overhead on average. The branch- prediction-based approach requires an extra pipeline stage for wake up, which adds to the branch misprediction penalty. Fortunately, this cost is mitigated because the extra wake-up stage is overlapped with misprediction recovery. This paper assumes the superdrowsy leakage control technique using reduced supply voltage because it is well suited to the instruction cache's criticality. However, the proposed policy can be also applied to other leakage- saving circuit techniques.