The TURBO Diaries: Application-controlled Frequency Scaling Explained

Most multi-core architectures nowadays support dynamic voltage and frequency scaling (DVFS) to adapt their speed to the system’s load and save energy. Some recent architectures additionally allow cores to operate at boosted speeds exceeding the nominal base frequency but within their thermal design power. In this paper, we propose a general-purpose library that allows selective control of DVFS from user space to accelerate multi-threaded applications and expose the potential of heterogeneous frequencies. We analyze the performance and energy trade-offs using different DVFS configuration strategies on several benchmarks and real-world workloads. With the focus on performance, we compare the latency of traditional strategies that halt or busy-wait on contended locks and show the power implications of boosting of the lock owner. We propose new strategies that assign heterogeneous and possibly boosted frequencies while all cores remain fully operational. This allows us to leverage performance gains at the application level while all threads continuously execute at different speeds. We also derive a model to help developers decide on the optimal DVFS configuration strategy, e.g, for lock implementations. Our indepth analysis and experimental evaluation of current hardware provides insightful guidelines for the design of future hardware power management and its operating system interface.