Snoopy Protocol

 

current snoopy protocol (performed on every instruction for ALL data, circa 1983)
on read - cache-hit - read from cache.
on read - cache miss - read from memory and store in cache.

on write - write-through and invalidate in EVERY cache.

Overhead increases as a binomial with the number of caches.

Invalidation occurs on writes for ALL data (because shared data is not identified).

Thread Safe Protocol:

Private data (mutex not required) - private cache - no protocol.

Shared data - read-through and write-through - no protocol

Swap data - execute-through - serialized in memory