Efficient Power Gating of SIMD Accelerators Through Dynamic Selective Devectorization in an HW/SW Codesigned Environment

Abstract

Leakage energy is a growing concern in current and future microprocessors. Functional units of microprocessors are responsible for a major fraction of this energy. Therefore, reducing functional unit leakage has received much attention in recent years. Power gating is one of the most widely used techniques to minimize leakage energy. Power gating turns off the functional units during the idle periods to reduce the leakage. Therefore, the amount of leakage energy savings is directly proportional to the idle time duration. This article focuses on increasing the idle interval for the higher SIMD lanes. The applications are profiled dynamically, in a hardware/software codesigned environment, to find the higher SIMD lanes' usage pattern. If the higher lanes need to be turned on for small time periods, the corresponding portion of the code is devectorized to keep the higher lanes off. The devectorized code is executed on the lowest SIMD lane. Our experimental results show that the average energy savings of the proposed mechanism are 15%, 12%, and 71% greater than power gating for SPECFP2006, Physicsbench, and Eigen benchmark suites, respectively. Moreover, the slowdown caused by devectorization is negligible.