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In-Network Snoop Ordering (INSO): Snoopy coherence on unordered interconnects | IEEE Conference Publication | IEEE Xplore

In-Network Snoop Ordering (INSO): Snoopy coherence on unordered interconnects


Abstract:

Realizing scalable cache coherence in the many-core era comes with a whole new set of constraints and opportunities. It is widely believed that multi-hop, unordered on-ch...Show More

Abstract:

Realizing scalable cache coherence in the many-core era comes with a whole new set of constraints and opportunities. It is widely believed that multi-hop, unordered on-chip networks would be needed in many-core chip multiprocessors (CMPs) to provide scalable on-chip communication. However, providing ordering among coherence transactions on unordered interconnects is a challenge. Traditional approaches for tackling coherence either have to use ordered interconnects (snoop-based protocols) which lead to scalability problems, or rely on an ordering point (directory-based protocols) which adds indirection latency. In this paper, we propose In-Network Snoop Ordering (INSO), in which coherence requests from a snoop-based protocol are inserted into the interconnect fabric and the network orders the requests in a distributed manner, creating a global ordering among requests. Essentially, when coherence requests enter the network, they grab snoop-orders at the injection router before being broadcasted. A snoop-order specifies the global ordering of the particular request with respect to other requests. Before requests reach their destinations, they get ordered along the way, at intermediate routers and destination network interfaces. Our logical ordering scheme can be mapped onto any unordered interconnect. This enables a cache coherence protocol which exploits the low-latency nature of unordered interconnects without adding indirection to coherence transactions. Our full-system evaluations compare INSO against a directory protocol and a broadcast based Token Coherence protocol. INSO outperforms these protocols by up to 30% and 8.5%, respectively, on a wide range of scientific and emerging applications.
Date of Conference: 14-18 February 2009
Date Added to IEEE Xplore: 06 March 2009
Print ISBN:978-1-4244-2932-5

ISSN Information:

Conference Location: Raleigh, NC, USA

References

References is not available for this document.