A Scalable Coherent Cache System With Incomplete Directory State.

Abstract

We describe a directory based coherent cache system which can be scaled. Our scheme is an interpolation between the complete directory state solution by Censier and Feautrier, where the memory controller knows the disposition of the line for every cache, and the minimal state solution due to Archibald and Baer which requires broadcasts for certain state transitions. By interpolating between these solutions, and providing efficient hardware support, we can reduce the negative performance impact of broadcasts to caches which do not have a copy of the line. 7 refs.