SigNet: Network-on-chip filtering for coarse vector directories

Abstract

Scalable cache coherence is imperative as systems move into the many-core era with cores counts numbering in the hundreds. Directory protocols are often favored as more scalable in terms of bandwidth requirements than broadcast protocols; however, directories incur storage overheads that can become prohibitive with large systems. In this paper, we explore the impact that reducing directory overheads has on the network-on-chip and propose SigNet to mitigate these issues. SigNet utilizes signatures within the network fabric to filter out extraneous requests prior to reaching their destination. Overall, we demonstrate average reductions in interconnect activity of 21% and latency improvements of 20% over a coarse vector directory while utilizing as little as 25% of the area of a full-map directory.