In this paper we study one kind of irregular computation on distributed arrays, the irregular prefix operation, that is currently not well taken into account by the standard data-parallel language HPF2. We show a parallel implementation that efficiently takes advantage of the independent computations arising in this irregular operation. Our approach is based on the use of a directive which characterizes an irregular prefix operation and on inspector/executor support, implemented in the CoLuMBO library, which optimizes the execution by using an asynchronous communication scheme and then communication/computation overlap. We validate our contribution with results achieved on IBM SP2 for basic experiments and for a sparse Cholesky factorization algorithm applied to real size problems.
['Frédéric Brégier', 'Marie Christine Counilh', 'Jean Roman']
Asynchronous progressive irregular prefix operation in HPF2