On hot-spot contention in interconnection networks

Abstract

A major component of a parallel machine is its interconnection network, which provides concurrent communication between the processing elements. It is common to use a multi-stage interconnection network (MIN) which is constructed using crossbar switches and introduces not only contention for destination addresses but also additional contention for internal switches. Both types of contention are increased when non-local communication across a MIN becomes concentrated on a certain destination address, for example when a frequently-accessed data structure is stored entirely in one element of a distributed memory. Such an address, often called a hot-spot , affects the blocking probability of paths to other destination addresses because of the shared internal switches. This paper describes an analytical model of hot-spot contention and quantifies its effect on the performance of a MIN with a circuit switching communication protocol. We obtain performance measures for a MIN in which partial paths are held during path building and one destination address is more frequently chosen by incoming traffic than other addresses.