An Effective Synchronization Network for Hot-Spot Accesses

In large multiprocessor systems, fast synchronization is crucial for high performance. However, synchronization traffic tends to create “hot-spots” in shared memory and cause network congestion. Multistage shuffle-exchange networks have been proposed and built to handle synchronization traffic. Software combining schemes have also been proposed to relieve network congestion caused by hot-spots. However, multistage combining networks could be very expensive and software combining could be very slow. In this paper, we propose a single-stage combining network to handle synchronization traffic, which is separated from the regular memory traffic. A single-stage combining network has several advantages: 1992 it is attractive from an implementation perspective because only one stage is needed(instead of log N stages); (2) Only one network is needed to handle both forward and returning requests; (3) combined requests are distributed evenly through the network—the wait buffer size is reduced; and (4) fast-finishing algorithms [30] can be used to shorten the network delay. Because of all these advantages, we show that a single-stage combining network gives good performance at a lower cost than a multistage combining network.