Drowsy Register Files for Reducing GPU Leakage Energy

General-purpose graphics processing units (GPGPUs) usually employ a huge register file (RF) to support massive multithreading, which however, is also responsible for a large fraction of GPGPU’s total power. In this paper, we propose three RF drowsy policies and evaluate their effectiveness on leakage energy reduction. In the first drowsy policy called immediate sleep (Drowsy-IS), registers keep staying in the drowsy mode unless they are accessed, which are then put into the drowsy mode again immediately to minimize the leakage energy consumption. The second policy named temporary awake (Drowsy-TA) holds the registers in the normal (i.e. active) mode for a certain period after being accessed to wait for the next access. The registers are placed into the drowsy mode until that period expires without any access activity. Finally, we propose an adaptive policy named Drowsy-RI which identifies the re-access interval for each register at run-time and lets registers wait for the predicted intervals before putting them into the drowsy mode. The experimental results show that compared to the baseline RF, Drowsy-IS achieves 91.7% RF leakage energy reduction on average at the cost of 4.4% performance degradation. Drowsy-TA leads to negligible performance overhead, and 82.8% leakage energy reduction. By balancing the energy saving and the performance overhead, Drowsy-RI saves more RF leakage energy (87.3%) than Drowsy-TA and achieves less performance degradation (2.7%) than Drowsy-IS.