Write completion for SC?
Needn’t wait for inval to actually happen
- Just wait till it gets bus
Commit versus complete
- Don’t know when inval actually inserted in destination process’s local order, only that it’s before next xaction and in same order for all procs
- Local write hits become visible not before next bus transaction
- Same argument will extend to more complex systems
- What matters is not when written data gets on the bus (write back), but when subsequent reads are guaranteed to see it
Write atomicity: if a read returns value of a write W, W has already gone to bus and therefore completed if it needed to