Efficient Mapping of Interdependent Scans

. Distributed memory multiprocessors are extremely sensitive to communication costs. Some global communications such as scans and reductions are of special interest since their cost is much lower than for point to point communications. Our paper focuses on an algorithm which efficiently takes the mapping of scans into account. 1 Introduction Communications remain the most critical aspect of performance in efficiently programming distributed memory multiprocessors. Hence minimizing communications is an indispensable task. A static placement may be obtained in two different ways: one may ask the user to insert annotations to specify data mapping `a la HPF. Our approach is to leave this work to the compiler (see 2). However such a placement will not be sufficient if some particularities of the target machine are not taken into account, for instance if communication primitives with low overhead are not used. In this paper we propose a method to compute a placement which efficiently exploi..