Maintaining snoop traffic throughput in presence of an atomic operation a first port for a first queue tracks cache requests and a second port for a second queue snoops that have yet to be filtered

Abstract

Apparatus and method to permit snoop filtering to occur while an atomic operation is pending. The snoop filtering apparatus includes first and second request queues and a cache. The first request queue tracks cache access requests, while the second request queue tracks snoops that have yet to be filtered. The cache includes a dedicated port for each request queue. The first port is dedicated to the first request queue and is a data-and-tag read-write port, permitting modification of both a cache line's data and tag. In contrast, the second port is dedicated to the second request queue and is a tag-only port. Because the second port is a tag-only port, snoop filtering can continue while a cache line is locked without fear of any modification of the data associated with the atomic address.