Microarchitectural Techniques for Power Gating of Execution Units

Leakage power is a major concern in current and future microprocessor designs. In this paper, we explore the potential of architectural techniques to reduce leakage through power-gating of execution units. This paper first develops parameterized analytical equations that estimate the break-even point for application of power-gating techniques. The potential for power gating execution units is then evaluated, for the range of relevant break-even points determined by the analytical equations, using a state-of-the-art out-of-order superscalar processor model. The power gating potential of the floating-point and fixed-point units of this processor is then evaluated using three different techniques to detect opportunities for entering sleep mode; ideal, time-based, and branch-misprediction-guided. Our results show that using the time-based approach, floating-point units can be put to sleep for up to 28% of the execution cycles at a performance loss of 2%. For the more difficult to power-gate fixed-point units, the branch misprediction guided technique allows the fixed-point units to be put to sleep for up to 40% more of the execution cycles compared to the simpler time-based technique, with similar performance impact. Overall, our experiments demonstrate that architectural techniques can be used effectively in power-gating execution units.