Distributing Hot-Spot Addressing in Large-Scale Multiprocessors

When a large number of processors try to access a common variable, referred to as hot-spot accesses in [6], not only can the resulting memory contention seriously degrade performance, but it can also cause tree saturation in the interconnection network which blocks both hot and regular requests alike. It is shown in [6] that even if only a small percentage of all requests are to a hot-spot, these requests can cause very serious performance problems, and networks that do the necessary combining of requests are suggested to keep the interconnection network and memory contention from becoming a bottleneck. Instead we propose a software combining tree, and we show that it is effective in decreasing memory contention and preventing tree saturation because it distributes hot-spot accesses over a software tree whose nodes can be dispersed over many memory modules. Thus, it is an inexpensive alternative to expensive combining networks.