Analysis of composite synchronization

Composite synchronization is a new algorithm that combines localized asynchronous coordination, with a global synchronization window. It was developed to simultaneously address the vulnerability of local synchronization to high model connectivity, and the vulnerability that a global window approach has to a very small minimal channel delay. Under composite synchronization, every channel is classified as being either synchronous or asynchronous; the behavior of the algorithm is then determined by the assignment. In an earlier work we proposed the algorithm, and showed that the channel assignment which minimizes the sum of all synchronization overhead, on an architecture with uniform memory access costs, has a threshold structure. The current paper extends that work, showing how speedup depends upon model topology, and that the assignment which maximizes speedup on a multi-cost memory system likewise has a threshold structure, but need not be exactly the same policy as that which minimizes total overhead.