Advanced Computer Architecture Chapter 7.43
Example Directory
Protocol
Message sent to directory causes two actions:
Update the directory
More messages to satisfy request
Block is in Uncached state: the
copy in memory is the current value; only possible
requests for that block are:Read miss: requesting processor
sent data from memory &requestor made only sharing node; state of block made Shared.
Write miss: requesting processor is
sent the value & becomes the Sharing node. The block
is made Exclusive to indicate that the only valid
copy is cached. Sharers indicates the identity of the owner.
Block is Shared => the
memory value is up-to-date:Read miss: requesting processor is
sent back the data from memory & requesting
processor is added to the sharing set.
Write miss: requesting processor is
sent the value. All processors in the set Sharers are sent
invalidate messages, & Sharers is set to identity
of requesting processor. The state of the block is made Exclusive.