The purpose of Exclusive Access is to read, calculate and modify a cache line atomically. The built-in Atomic Transactions can do some basic calculations at ICN or SN, but if more complex operations are necessary, Exclusive Access is needed.
CHI specification rules that during an Exclusive Transaction to a snoopable region, when the addressed location is updated by other Logical Processor(LP), or is targeted by an Exclusive Store from another LP that is permitted to proceed, this Exclusive Transaction must fail.
So whats the difference between these two conditions? One Exclusive Access being interrupted by another Exclusive Access should fail the former one, essentially because the addressed location is updated by the latter one and the transaction is not atomic any longer. Isn\'t this one special case of the first condition that the targeted memory is updated? |
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