Real-time and energy efficiency in Linux: theory and practice

The recent changes made in the Linux kernel aimed at achieving better energy efficiency through a tighter integration between the CPU scheduler and the frequency-scaling subsystem. However, in the original implementation, the frequency scaling mechanism was used only when there were no realtime tasks in execution. This paper shows how the deadline scheduler and the cpufreq subsystem have been extended to relax this constraint and implement an energy-aware realtime scheduling algorithm. In particular, we describe the design issues encountered when implementing the GRUB-PA algorithm on a real operating system like Linux. A set of experimental results on a multi-core ARM platform validate the effectiveness of the proposed implementation, which has been recently merged into the official Linux kernel.