MVAPICH2-X (Unified MPI+PGAS Communication Runtime over OpenFabrics/Gen2 for Exascale Systems)
Message Passing Interface (MPI) has been the most popular programming model for developing parallel scientific applications. Partitioned Global Address Space (PGAS) programming models are an attractive alternative for designing applications with irregular communication patterns. They improve programmability by providing a shared memory abstraction while exposing locality control required for performance. It is widely believed that hybrid programming model (MPI+X, where X is a PGAS model) is optimal for many scientific computing problems, especially for exascale computing.
MVAPICH2-X provides a unified high-performance runtime that supports both MPI and PGAS programming models on InfiniBand clusters. It enables developers to port parts of large MPI applications that are suited for PGAS programming model. This minimizes the development overheads that have been a huge deterrent in porting MPI applications to use PGAS models. The unified runtime also delivers superior performance compared to using separate MPI and PGAS libraries by optimizing use of network and memory resources.
MVAPICH2-X supports Unified Parallel C (UPC) and OpenSHMEM as PGAS models. It can be used to run pure MPI, MPI+OpenMP, pure UPC, pure OpenSHMEM as well as hybrid MPI(+OpenMP) + PGAS applications. MVAPICH2-X derives from the popular MVAPICH2 library and inherits many of its features for performance and scalability of MPI communication. It takes advantage of the RDMA features offered by the InfiniBand interconnect to support UPC/OpenSHMEM data transfer and atomic operations. It also provides a high-performance shared memory channel for multi-core InfiniBand clusters.
The MPI implementation of MVAPICH2-X is based on MVAPICH2, which supports all MPI-3 features. The UPC implementation is UPC Language Specification v1.2 standard compliant and is based on Berkeley UPC v2.18.0. OpenSHMEM implementation is OpenSHMEM v1.0 standard compliant and is based on OpenSHMEM Reference Implementation v1.0f. The current release supports communication using InfiniBand Transport (inter-node) and Shared Memory (intra-node). The overall architecture of MVAPICH2-X is shown in the figure below.