Opteron servers

Produced from IEEE Micro

AMD Hammer protocol

• Opteron uses the snoop-based Hammer protocol
  • First the requester sends a transaction to home node
  • The home node starts accessing main memory and in parallel broadcasts the request to all the nodes via point-to-point messages
  • The nodes individually snoop the request, take appropriate coherence actions in their local caches, and sends data (if someone has it in M or O state) or an empty completion acknowledgment to the requester; the home memory also sends the data speculatively
  • After gathering all responses the requester sends a completion message to the home node so that it can proceed with subsequent requests (this completion ack may be needed for serializing conflicting requests)
  • This is one example of a snoopy protocol over a point-to-point interconnect unlike the shared bus