amba-chi · Topic
MSI, MESI, MOESI & MESIF Coherence Protocols
The classic coherence state families — what each state means, what each protocol adds, and the traffic it saves.
Each protocol in this family adds one state to solve one specific inefficiency. MESI adds Exclusive so a read followed by a write need not broadcast twice. MOESI adds Owned so dirty data can be shared without writing back first. MESIF adds Forward so exactly one sharer answers a request. Reading them as a sequence of targeted optimisations is far more useful than memorising four state diagrams.