Reducing Functional Unit Power Consumption and its Variation Using Leakage Sensors

Energy reduction of functional units (FUs) is a very important concern for high-end superscalar processors, not only because FUs consume a significant portion of processor energy, but also because they are one of the most important hotspots in the processor. In addition, the high sensitivity of leakage on temperature and process variation result in very high variation in the FU power consumption in different processor dies. Such high process variation reduces the parametric yield of processors. Consequently, reducing the FU power consumption and its variation is an important problem. However, existing FU power reduction techniques assumes all the FUs are similar, and do not consider the sensitivity of leakage on temperature. Consequently, they are not very effective in reducing the variation of FU power consumption. The advent of extremely small, yet accurate leakage sensors allow us to develop leakage-aware microarchitectural techniques to reduce both the power consumption and its variation among processor dies. Our leakage-aware operation-to-FU binding mechanism (LAOFBM) and leakage-aware power gating (LA-PG) mechanisms reduce the mean and standard deviation of the total arithmetic logic unit (ALU) power consumption of the ALPHA 21364 by 34% and 59%, respectively. At the processor level, this translates to a 13% reduction in the total processor energy consumption, with a 24°C reduction in the maximum ALU temperature.