Multicast Snooping: A New Coherence Method Using a Multicast Address Network

This paper proposes a new coherence method called "multicast snooping" that dynamically adapts between broadcast snooping and a directory protocol. Multicast snooping is unique because processors predict which caches should snoop each coherence transaction by specifying a multicast "mask." Transactions are delivered with an ordered multicast network, such as an Isotach network, which eliminates the need for acknowledgment messages. Processors handle transactions as they would with a snooping protocol, while a simplified directory operates in parallel to check masks and gracefully handle incorrect ones (e.g., previous owner missing). Preliminary performance numbers with mostly SPLASH-2 benchmarks running on 32 processors show that we can limit multicasts to an average of 2-6 destinations (<< 32) and we can deliver 2-5 multicasts per network cycle (>> broadcast snooping's 1 per cycle). While these results do not include timing, they do provide encour...

• Type: Conference
• Year: 1999
• Where: ISCA
• Authors: E. Ender Bilir, Ross M. Dickson, Ying Hu, Manoj Plakal, Daniel J. Sorin, Mark D. Hill, David A. Wood
• Keywords: Broadcast Snooping, Hardware, ISCA 1999, Multicast Network, Multicast Snooping