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sushi

Seems that BusUpd is in Dragon write-back update protocol, but there's no BusRdX transaction in that protocol. So what's protocol this example applies to?

kayvonf

Here, BusUpg (upgrade) is a transition from S to M in MESI. (It's an upgrade, not a BusRdX, since memory does not need to respond, although both take exclusive write ownership of the line.). I left it out of the MESI protocol diagram in the snooping lecture for simplicity them. I should update that diagram to be more accurate.

rrp123

How hard would to be for us to actually implement this ability to change requests on the fly? Or has it already been done? I think it would be pretty hard, since then the processor has to keep track of a lot more requests than initially indicated.