Deterministic clock gating for microprocessor power reduction

Abstract

With the scaling of technology and the need for higher performance and more functionality, power dissipation is becoming a major bottleneck for microprocessor designs. Pipeline balancing (PLB), a previous technique, is essentially a methodology to clock-gate unused components whenever a program's instruction-level parallelism is predicted to be low. However, no nonpredictive methodologies are available in the literature for efficient clock gating. This paper introduces deterministic clock gating (DCG) based on the key observation that for many of the stages in a modern pipeline, a circuit block's usage in a specific cycle in the near future is deterministically known a few cycles ahead of time. Our experiments show an average of 19.9% reduction in processor power with virtually no performance loss for an 8-issue, out-of-order superscalar processor by applying DCG to execution units, pipeline latches, D-Cache wordline decoders, and result bus drivers. In contrast, PLB achieves 9.9% average power savings at 2.9% performance loss.