Energy Minimization for Multi-core Platforms through DVFS and VR Phase Scaling With Comprehensive Convex Model

Energy management is a critical challenge in multi-core processors due to continuous technology scaling. Previous methods have mostly focused on the energy minimization of the processor cores. However, energy overhead of the off-chip voltage regulator (VR) has recently shown to be a non-trivial part of the total energy consumption and has been previously overlooked. In this paper, we propose an overall energy optimization method for the system that minimizes both per-core energy consumption and VR energy consumption using dynamic voltage frequency scaling (DVFS) and VR phase scaling by solving a comprehensive convex model. In order to improve the accuracy of the task latency model, a new task model considering both computation and memory access of the task is also developed. Furthermore, for better scalability and lower on-line overhead, we decompose our proposed convex method into two stages: an off-line stage and an on-line stage. During the off-line stage, we explore the convex model by assuming different numbers of active phases of the VR, various workload pressures and workload characteristics to collect the optimal frequency assignments under different scenarios. During the online stage, the specific frequency assignment for cores and optimal active phase number of the VR are selected and applied based on the actual workload pressure and its characteristics running on the cores. Experiments on real benchmarks show that when compared with state-of-the-art approaches, which are oblivious to VR overheads and exploit slack time to achieve energy minimization, our method can achieve a significant energy saving of up to 22.4% with negligible on-line overhead.