On-demand Connection Management for OpenSHMEM and OpenSHMEM+MPI

Partitioned Global Address Space (PGAS) programming models like Open SHMEM and hybrid models like Open SHMEM+MPI can deliver high performance and improved programmability. However, current implementations of Open SHMEM assume a fully-connected process model which affects their performance and scalability. We address this critical issue by designing on-demand connection management support for Open SHMEM which significantly improves the startup performance and reduces the resource usage. We further enhance the Open SHMEM startup performance by utilizing non-blocking out-of-band communication APIs. We evaluate our designs using a set of micro benchmarks and applications and observe 30 times reduction in Open SHMEM initialization time and 8.3 times improvement in execution time of a Hello World application at 8,192 processes. In particular, when sufficient work can be overlapped, we show that use of non-blocking out-of-band communication APIs allow for a constant initialization cost of Open SHMEM jobs at different core counts. We also obtain up to 90% reduction in number of network endpoints and up to 35% improvement in application execution time with NAS Parallel Benchmarks.