Automatic methods for hiding latency in parallel and distributed computation

In this paper we describe methods for mitigating the degradation in perform ance caused by high latencies in parallel and distributed networks. For exa mple, given any "dataflow" type of algorithm that runs in T steps on an n-n ode ring with unit link delays, we show how to run the algorithm in O(T) st eps on any n-node bounded-degree connected network with average link delay O(1). This is a significant improvement over prior approaches to latency hi ding, which require slowdowns proportional to the maximum link delay. In th e case when the network has average link delay d(ave), our simulation runs in O(root d(ave)T) steps using n/root d(ave) processors, thereby preserving efficiency. We also show how to efficiently simulate an n x n array with u nit link delays using slowdown (O) over tilde(d(ave)(2/3)) on a two-dimensi onal array with average link delay d(ave). Last, we present results for the case in which large local databases are involved in the computation.