REDUCING THE READ-MISS PENALTY FOR FLAT COMA PROTOCOLS

In flat cache-only memory architectures (COMA), an attraction-memory m iss must first interrogate a directory before a copy of the requested data can be located, which often involves three network traversals, By keeping track of the identity of a potential holder of the copy-calle d a hint-one network traversal can be saved which reduces the read pen alty, We have evaluated the reduction of the read-miss penalty provide d by hints using detailed architectural simulations and four benchmark applications. The results show that a previously proposed protocol us ing hints can actually make the read-miss penalty larger because when the hint is not correct, an extra network traversal is needed. This ha s motivated us to study a new protocol, using hints, that simultaneous ly sends a request to the potential holder and to the directory, This protocol reduces the read-miss penalty for all applications but the pr otocol complexity does not seem to justify the performance improvement .