A study of the efficiency of shared attraction memories in cluster-based COMA multiprocessors

The performance of a COMA multiprocessor greatly depends on the efficiency of the large node caches, the attraction memories. When more than one processor share an attraction memory its behavior is changed. From experiments with program-driven simulation we have found that clustering may improve the performance of the attraction memory significantly. Traffic is reduced, and the miss rates are lower for shared attraction memories. However clustering may introduce contention for the attraction memory that may ruin any potential performance gain from increased attraction memory hit rate. Provided enough local bandwidth, application execution can remain efficient at higher memory pressure in clustered systems than in systems with single processor nodes. Ar very high memory pressure some applications change behavior and start suffering from clustering. This is caused by conflict misses due to the relatively lower associativity of the shared attraction memory.