Experimenting with low-overhead OpenMP runtime on IBM Blue Gene/Q

As newer supercomputers continue to increase the number of threads, there is growing pressure on applications to exploit more of the available parallelism in their codes, including coarse-, medium-, and fine-grain parallelism. OpenMP (TM) is one of the dominant shared-memory programming models and is well suited for exploiting medium- and fine-grain parallelism. OpenMP research has focused on application tuning, compiler optimizations, programming-model extensions, and porting to distributed-memory platforms; however, we have found that current algorithms used to implement basic OpenMP constructs have significant overheads and scale poorly. In this paper, we explore low-overhead, scalable algorithms for creating parallel regions and demonstrate reductions in overhead of up to a factor of 5 on an IBM Blue Gene (R)/Q node.