Reducing communication overhead is a key goal of program optimization for current scalable multiprocessors. A well-known approach to achieving this is to map tasks (indivisible units of computation) to processors so that communication and computation overlap as much as possible. In an earlier work, we developed a look-ahead scheduling heuristic for efficiently reducing communication overhead with the aim of decreasing the completion time of a given parallel program. In this paper, we report on an extension of the algorithm, which fills in the idle time slots created by interprocessor communication without increasing the algorithm's time complexity. The results of experiments emphasize the importance of optimally filling idle time slots in processors.

The main contribution of this work is to propose energy-efficient randomized initialization protocols for ad-hoc radio networks (ARN, for short). First, we show that if the number n of stations is known beforehand, the single-channel ARN can be initialized by a protocol that terminates, with high probability, in O(n) time slots with no station being awake for more than O(log n) time slots. We then go on to address the case where the number n of stations in the ARN is not known beforehand. We begin by discussing, an elegant protocol that provides a tight approximation of n. Interestingly, this protocol terminates, with high probability, in O((log n)2) time slots and no station has to be awake for more than O(log n) time slots. We use this protocol to design an energy-efficient initialization protocol that terminates, with high probability, in O(n) time slots with no station being awake for more than O(log n) time slots. Finally, we design an energy-efficient initialization protocol for the k-channel ARN that terminates, with high probability, in O(n/k+log n) time slots, with no station being awake for more than O(log n) time slots.