Using Proxies to Reduce Controller Contention in Large Shared-Memory Multiprocessors

Some shared-memory applications have execution times linear in the number of processors due to unfortunate allocation of the home and ownership of cache lines. We present a modified coherency protocol which avoids this effect. Read requests are routed via "proxies", randomly-selected intermediate nodes. We present results from executiondriven simulations of a cc-numa architecture which show that proxying can yield a large speedup in cases where read contention is extreme, while only causing small slowdowns in other benchmarks. We investigate how many proxies should be used and what effect the scheme has on traffic levels and queuing of requests at node controllers