Transient Congestion Avoidance in Software Distributed Shared Memory Systems

OpenMP applications executed on top of software distributed shared memory (SDSM) systems show peaks in network traffic. In these scenarios, synchronization points are used to maintain memory consistency and improve performance, and network traffic is highly increased due to data being exchanged between different nodes in the system. This behaviour generates network congestion which may limit or degrade applications performance. In this paper we present a technique to avoid these peaks by sending data producing the congestion earlier in time. Our proposal is to introduce virtual synchronization points between the real ones, and use them to automatically distribute the network traffic. This technique is evaluated with a synthetic benchmark, and with the classes A and B of two OpenMP codes from the NAS benchmarks (BT and CG), on top of NanosDSM, a page-based DSM implementing sequential consistency. The results show a 16% performance improvement on average over the traditional methods.