Limited Combining Strategies for Large-Scale Shared-Memory Multiprocessors

In a large-scale shared-memory multiprocessor, there is a possibility of serious contention due to many requests issued concurrently for the same memory location. A multistage combining network, in which each switch is enhanced with combining so that multiple requests directed to the same memory location can form a single request, significantly reduces the amount of the contention. However, employing combining in every switch of a multistage interconnection network tends to increase the cost and to slow down the network. In this paper, assuming a single-job environment, we investigate some simple strategies that allow only a limited portion of a network to have a combining capability. We show that for situations with a limited number of hot spot locations, these simple strategies can provide performance comparable to a complete combining network in which every switch is enhanced with combining