What is another way to evaluate the transactions that occur in an invalidation protocol?
A14.1: BusRd is equivalent to a read from main memory. PrRd is equivalent to a read from a local cache. A flush means to copy the latest value from a cache to main memory. A BusRdX just means that only one cache has the updated cache value. BusRd(~S) means generate this BusRd transaction only if the cache value is not shared (or modified) somewhere else. Similarly, BusRd(S) means generate this BusRd transaction only if the cache value is already shared (or modified or exclusive) elsewhere. Q14.2: Can a processor write to a block that it hasn’t read? I was going back through the notes and I thought it could, but I’m unsure. For example, If a P2 read u, could P3 write u=5 without having read it first? A14.2: Definitely. This is exactly the situation we were talking about in Lecture 11 when we discussed write allocate vs. no write allocate.
