Store buffer supporting direct stores to a coherence point

Abstract

A system that uses a write-invalidate protocol has two types of stores: a traditional store that operates using a write-back policy that snoops for copies of the cache line at lower cache levels, and a store that writes, using a coherent write-through policy, directly to the last-level cache without snooping the lower cache levels. A separate store buffer may be maintained in the processor for the coherent write-through operations. A special bit may be maintained in the entries of a store buffer that is used for both traditional write-back policy stores and for coherent write-through policy. This bit indicates that loads and stores older than the last speculative store in the store buffer are allowed to be performed.