amba-chi · Topic
Cache Coherency Foundations — Why Coherence Protocols Exist
The problem coherence solves — private caches, shared memory, and the guarantees a coherence protocol must provide.
Coherence exists because caches are private and memory is shared. Once two agents can each hold a copy of the same line, something must guarantee that a read returns a value consistent with the writes that happened. Every coherence protocol is a different answer to that question, and the differences are mostly about how much traffic they spend to keep the guarantee.