Warped gates: Gating aware scheduling and power gating for GPGPUs

With the widespread adoption of GPGPUs in varied application domains, new opportunities open up to improve GPGPU energy efficiency. Due to inherent application-level inefficiencies, GPGPU execution units experience significant idle time. In this work we propose to power gate idle execution units to eliminate leakage power, which is becoming a significant concern with technology scaling. We show that GPGPU execution units are idle for short windows of time and conventional microprocessor power gating techniques cannot fully exploit these idle windows efficiently due to power gating overhead. Current warp schedulers greedily intersperse integer and floating point instructions, which limit power gating opportunities for any given execution unit type. In order to improve power gating opportunities in GPGPU execution units, we propose a Gating Aware Two-level warp scheduler (GATES) that issues clusters of instructions of the same type before switching to another instruction type. We also propose a new power gating scheme, called Blackout, that forces a power gated execution unit to sleep for at least the break-even time necessary to overcome the power gating overhead before returning to the active state. The combination of GATES and Blackout, which we call Warped Gates, can save 31.6% and 46.5% of integer and floating point unit static energy. The proposed solutions suffer less than 1% performance and area overhead.