Integrating Processor Slowdown and Preemption Threshold Scheduling for Energy Efficiency in Real Time Embedded Systems

Preemption threshold scheduling (PTS) enables designing scalable real-time systems. PTS not only decreases the run-time overhead of the system, but can also be used to decreases the number of threads and the memory requirements of the system. In this paper, we combine preemption threshold scheduling with dynamic voltage scaling to enable energy efficient scheduling in real time systems. We consider PTS with task priorities defined by the earliest deadline first policy. We present an algorithm to compute threshold preemption levels for tasks with given static slowdown factors. The proposed algorithm improves upon known algorithm in terms of time complexity. Using our approach, we show that PTS can be used to substantially minimize the context switching overhead even in the presence of slowdown. Experimental results show that preemption threshold scheduling reduces the context switches by 50% - 90%. Further, we describe a dynamic slack reclamation technique that working in conjunction with PTS and yields further energy gains from 10-50% depending upon availability of slack