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
.