A voltage scheduling heuristic for real-time task graphs

Abstract

Energy constrained complex real-time systems are becoming increasingly important in defense, space, and consumer applications. In this paper, we present a sensible heuristic to address the problem of energy-efficient voltage scheduling of a hard real-time task graph with precedence constraints for a multi-processor environment. We show that consideration of inter-relationships among the tasks in a holisitic way can lead to an effective heuristic for reducing energy expenditure. We developed this algorithm for systems running with two voltage levels since this is currently supported by a majority of modern processors. We then extend the algorithm for processors that can support multiple voltage levels. The results show that substantial energy savings can be achieved by using our scheme. The algorithm is then compared with other relevant algorithms derived for hypothetical systems which can run on infinite voltage levels in a given range. Our two voltage systems, using the task dependencies effectively, can provide a comparable performance with those algorithms in the cases where continuous voltage switching is not allowed.