ExSched: An External CPU Scheduler Framework for Real-Time Systems

Scheduling theory and algorithms have been well studied in the real-time systems literature. Many useful approaches and solutions have appeared in different problem domains. While their theoretical effectiveness has been extensively discussed, the community is now facing implementation challenges that show the impact of the algorithms in practice. In this paper, we propose a scheduler framework, called ExSched, which enables different schedulers to be developed for different operating system (OS) platforms without any modifications to the OS itself, using a unified interface. The framework will easily keep up with changes in the kernel since it is only dependent on a few kernel primitives. The usefulness of this framework is that scheduling policies can be implemented as external plug-ins. They can simply use the ExSched interface instead of platform-dependent functions, since platform details are abstracted by ExSched. The advantage for industry is that they would more easily keep up with new kernel versions since ExSched does not require patches. The advantage for academia is that we could focus on the development of schedulers instead of tedious and time-consuming installations of patched kernels. Our prototype implementation of ExSched supports Linux and Vx Works and it comes with example schedulers which include hierarchical and multi-core schedulers in addition to traditional fixed-priority scheduling (FPS) and earliest deadline first (EDF) algorithms.