Bringing real-time scheduling theory and practice closer for multimedia computing

This paper seeks to bridge the gap between theory and practice of real-time scheduling in the domain of high speed multimedia networking. We show that the strict preemptive nature of real-time scheduling leads to more context switching, and requires system calls for concurrency control. We present our scheduling scheme called rate-monotonic with delayed preemption (rmdp) and show how it reduces both these overheads. We then develop the analytical framework to analyze rmdp and other scheduling schemes that lie in the region between strict (immediate) preemption and no preemption. Our idealized scheduler simulation methodology accounts for the blocking introduced by these schemes under the usual assumption that the time for context switching and preemption is zero. We derive simpler schedulability tests for non-preemptive scheduling, and prove a variant of rate-monotonic scheduling that has fewer preemptions. Our measurements on Sparc and Pentium platforms, show that for the workloads we considered, Rmdp increases useful utilization by as much as 8%. Thus our scheduling policies have the potential to improve performance over existing methods.