A Superassociative Tagged Cache Coherence Directory

Dynamically tagged directories are memory-efficient mechanisms for maintaining cache coherence in sharedmemory multiprocessors. These directories use specialpurpose caches of pointers that are subject to two types of overflow: 1) pointer overflow, which limits the maximum sharing of a memory block, and 2) set overflow, which forces the premature invalidation of cached blocks. We propose a superassociative tagged directory that can preserve some of the cached copies of a memory block when a set overflows by allowing multiple address tags in the same set to contain the same address value. Verilog descriptions are used to estimate its implementation cost and timing delay, and a multiprocessor cache simulator is used to evaluate its performance.