Contention elimination by replication of sequential sections in distributed shared memory programs

In shared memory programs contention often occurs at the transition between a sequential and a parallel section of the code. As all threads start exec uting the parallel section, they often access data just modified by the thr ead that executed the sequential section, causing a flurry of data requests to converge on that processor. We address this problem in a software distributed shared memory system by r eplicating the execution of the sequential sections on all processors. Comm unication during this replicated sequential execution is reduced by using m ulticast. We have implemented replicated sequential execution with multicast support in Open MP/NOW, a version of of OpenMP that runs on networks of workstation s. We do not rely on compile-time data analysis, and therefore we can handl e irregular and pointer-based applications. We show significant improvement for two pointer-based applications that suffer from severe contention with out replicated sequential execution.