Natively supporting true one-sided communication in MPI on multi-core systems with infiniband

As high-end computing systems continue to grow in scale, the performance that applications can achieve on such large scale systems depends heavily on their ability to avoid explicitly synchronized communication with other processes in the system. Accordingly, several modern and legacy parallel programming models (such as MPI, UPC, Global Arrays) have provided many programming constructs that enable implicit communication using one-sided communication operations. While MPI is the most widely used communication model for scientific computing, the usage of one-sided communication is restricted; this is mainly owing to the inefficiencies in current MPI implementations that internally rely on synchronization between processes even during one-sided communication, thus losing the potential of such constructs. In our previous work, we had utilized native one-sided communication primitives offered by high-speed networks such as InfiniBand (IB) to allow for true one-sided communication in MPI. In this paper, we extend this work to natively take advantage of one-sided atomic operations on cache-coherent multi-core/multi- processor architectures while still utilizing the benefitts of networks such as IB. Specifically, we present a sophisticated hybrid design that uses locks that migrate between IB hardware atomics and multi-core CPU atomics to take advantage of both. We demonstrate the capability of our proposed design with a wide range of experiments illustrating its benefits in performance as well as its potential to avoid explicit synchronization.