Memory references not cached at a cluster must be sent to the home. The home can satisfy the reference directly in all cases except when the data is dirty in a remote cluster. A reference is local to the home if the memory is allocated at that referring cluster. References that are not local to the home require two network hops and take 100 cycles. References requiring three hops, because the data is dirty in another cluster take 150 cycles.
Memory is allocated to clusters when first touched on a round robin basis.
Some application programs explicitly place data when such placement improves performance. All stack references are allocated locally. To exclude the effect of conflict misses from the performance characterizations, the caches that are simulated are fully associative caches with an LRU replacement policy. For this reason we do not want to include the effect of conflict misses that are due to limited associativity. We use an estimation procedure to account for the increase in hit times from the shared cache.