Overlapping techniques of communications

We present in this paper general techniques for overlapping communications in parallel numerical kernels. We describe first some dependencies schemes which can be found in most of numerical parallel algorithms and we apply on these schemes methods based on the change of the granularity of the computational tasks. The choice of the granularity in order to obtain a good overlap depends on the main parameters of the target machines. We apply the precedent techniques of overlapping on classical numerical kernels, namely: the matrix-vector product and the bi-dimensional FFT, and implemented them on a T3D and a Paragon. The results of these experiments demonstrate the accuracy of this approach.