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In response to the remarkable increase in 3D applications in mobile devices in recent years, mobile GPUs have become widely available. Although the computation requirements are tremendous of 3D applications, they are highly data parallel operations. Therefore, mobile GPUs are usually hardware multithreaded to increase their throughput and achieve real-time rendering. This design increases energy consumption by duplicate register files in shaders. However, the register usage of shading programs is often relatively low, which causes many duplicated registers to go unused, and thus wastes energy. In addition, long latency memory operations can consume unnecessary energy to activate registers as well. This study proposes a compiler-assisted energy-efficient demand-driven register file (EDRF) to reduce energy consumptions of registers that are unused and waiting for long latency memory operations. The proposed EDRF is shared on demand between concurrent threads with multiple power gating modes. The management scheme of EDRF puts registers into different power modes to save leakage energy. In addition, the partitioned structure of EDRF saves dynamic energy for accessing registers. Results show that the average dynamic and leakage energy reduction ratios are 84.18% and 99.20%, respectively. Furthermore, the performance degradation from the proposed EDRF is only 0.50% on average.

Mobile GPUs are used in modern portable devices to satisfy the growing requirements of 3D applications. These GPUs generally integrate hardware multithreaded shaders to improve the throughput for real-time rendering, but they depend on duplicate register files to maintain the context of each hardware thread. This work develops a demand-driven register file (DDRF) to reduce the power consumption by register files. The proposed DDRF is shared on demand among concurrent threads and turns off almost all unused registers. Experimental results reveal the DDRF uses 85.8% less power than a conventional multithreaded GPU. The chip area and circuit latency of DDRF are also discussed. Keywords: register file, demand-driven, GPU, mobile Classification: Electron devices, circuits, and systems References[1] D. Brooks, V. Tiwari, and M. Martonosi, "Wattch: a framework for architectural-level power analysis and optimizations,"