Eliminating Invalidation in Coherent-Cache Parallel Graph Reduction

Parallel functional programs based on the graph reduction execution model display considerable locality of reference, favouring the use of large cache lines in the implementation of the shared heap on a shared-memory multiprocessor. They also display a very high rate of synchronisation, making conventional weakly-consistent coherency protocols ineeective at avoiding unnecessary contention for write access to cache lines due to false sharing. We present the design of a specially adapted cache coherency protocol and show results of simulation experiments which demonstrate that the protocol allows spatial locality to be exploited to at least the level of a conventional invalidation protocol, but without the unnecessary serialisation and network transactions caused by false sharing.