The switched snooping protocol above supports sequential consistency in part by making sure that reads are not performed while another node has a writeable block and writes are not performed while another processor has a writeable block. A more aggressive protocol will actually perform a write operation as soon as it receives its own Get Modified request, merging the newly written word(s) with the rest of the block when the data message arrives. This may appear illegal, since another node could simultaneously be writing the block. However, the global order required by sequential consistency is determined by the order of coherence requests on the address network, so the other node's write(s) will be ordered before the requester's write(s). Note that this optimization does not change the memory consistency model.
Assuming the parameters in Figure 4.41:
a. How significant would this optimization be for an in-order core?
b. How significant would this optimization be for an out-of-order core?