Co-Cap: energy-efficient cooperative CPU-GPU frequency capping for mobile games

Mobile platforms are increasingly using Heterogeneous Multi-Processor Systems-on-Chip (HMPSoCs) with differentiated processing cores and GPUs to achieve high performance for graphics-intensive applications such as mobile games. Traditionally, separate CPU and GPU governors are deployed in order to achieve energy efficiency through Dynamic Voltage Frequency Scaling (DVFS), but miss opportunities for further energy savings through coordinated system-level application of DVFS. We present Co-Cap, a cooperative CPU-GPU DVFS strategy that orchestrates energy-efficient CPU and GPU DVFS through coordinated CPU and GPU frequency capping to avoid frequency over-provisioning while maintaining desired performance. Unlike traditional approaches that target a narrow set of mobile games, our Co-Cap approach is applicable across a wide range of mobile games. Our methodology deploys a training phase followed by a deployment phase, allowing not only deployment across a wide range of mobile games with varying graphics workloads, but also across new mobile architectural platforms. Our experimental results across a large set of over 70 mobile games show that Co-Cap improves energy per frame by 10.6% and 10.0% (23.1% and 19.1% in CPU dominant applications) on average and achieves minimal frames per second (FPS) loss by 0.5% and 0.7% (1.3% and 1.7% in CPU dominant applications) on average in training- and deployment sets, respectively, compared to the default CPU and GPU governors, with negligible overhead in execution time and power consumption on the ODROID-XU3 platform.