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MOSI Protocol
- Some SMPs do not support the E state
- In many cases it is not helpful, only complicates the protocol
- MOSI allows a compact state encoding in 2 bits
- Sun WildFire uses MOSI protocol
Hybrid inval+update
- One possible hybrid protocol
- Keep a counter per cache line and make Dragon update protocol the default
- Every time the local processor accesses a cache line set its counter to some pre-defined threshold k
- On each received update decrease the counter by one
- When the counter reaches zero, the line is locally invalidated hoping that eventually the writer will switch to M state from Sm state when no sharers are left
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