Serialization
•The
bus defines the ordering on writes in SMPs
•For
directory systems, memory (home) does
•If
home always has value, FIFO would work
–Consider a block in modified state and two nodes requesting
exclusive access in an invalidation protocol: The requests reach home in one
order, but
they could reach the owner in a different order; which order
prevails?
•Fix:
Add “busy state” indicating transaction in flight