Lower Bounds on Communication Loads and Optimal Placements in Torus Networks

  • Authors:
  • Affiliations:
  • Venue:
  • IPPS '98 Proceedings of the 12th. International Parallel Processing Symposium on International Parallel Processing Symposium
  • Year:
  • 1998

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Abstract

Fully-populated tori, where every node has a processor attached, do not scale well since load on edges increases superlinearly with network size under heavy communication, resulting in a degradation in network throughput. In a partially-populated network, processors are placed on a subset of available nodes, and a routing algorithm is specified among the processors.Analogous to multistage networks, it is desirable to have the total number of messages being routed through a particular edge increase at most linearly with the size of the placement on torus networks. Recently, Blaum, Bruck, Pifarr茅 and Sanz investigated placements and provided both a lower bound, and optimal placements in the cases of 2 and 3-dimensional k-tori, consisting of k and k2 processors, respectively.In this paper we show formally that to achieve linear load in a d-dimensional k-torus, the number of processors in the placement must be O(kd-1). We use this to construct a tighter lower bound for the maximum load of a placement for 4 or more dimensions. Based on these results, we give optimal placements and their corresponding routing algorithms in tori with arbitrary number of dimensions.