Speculative Supplier Identification for Reducing Power of Interconnects in Snoopy Cache Coherence Protocols

In this work we reduce interconnect power dissipation in Symmetric Multiprocessors or SMPs. We revisit snoopy cache coherence protocols and reduce unnecessary interconnect activity by speculating nodes expected to provide a missing data. Conventional snoopy cache coherence protocols broadcast requests to all nodes, reducing the latency of cache to cache transfer misses at the expense of increasing interconnect power. We show that it is possible to reduce the associated power dissipation if such requests are broadcasted selectively and only to nodes more likely to provide the missing data. We reduce power as we limit access only to the interconnect components between the requester and the supplier node. We evaluate our technique using shared memory applications and show that it is possible to reduce interconnect power by 21 % in a 4-way multiprocessor without compromising performance. This comes with negligible hardware overhead