Publications

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Scope and Objectives: Kokkos Support provides cyber resources and conducts training events for current and prospective Kokkos users; In person training events are organized in various venues providing both generic Kokkos tutorials with lectures and exercises, as well as hands-on work on users applications.

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Sparse matrix-matrix multiplication is a key kernel that has applications in several domains such as scientific computing and graph analysis. Several algorithms have been studied in the past for this foundational kernel. In this paper, we develop parallel algorithms for sparse matrix-matrix multiplication with a focus on performance portability across different high performance computing architectures. The performance of these algorithms depend on the data structures used in them. We compare different types of accumulators in these algorithms and demonstrate the performance difference between these data structures. Furthermore, we develop a meta-algorithm, KKSPGEMM, to choose the right algorithm and data structure based on the characteristics of the problem. We show performance comparisons on three architectures and demonstrate the need for the community to develop two phase sparse matrix-matrix multiplication implementations for efficient reuse of the data structures involved.

This report documents the completion of milestone STPRO4-4 Kokkos back-ends research, collaborations, development, optimization, and documentation. The Kokkos team updated its existing backend to support the software stack and hardware of DOE's Sierra, Summit and Astra machines. They also collaborated with ECP PathForward vendors on developing backends for possible exa-scale architectures. Furthermore, the team ramped up its engagement with the ISO/C++ committee to accelerate the adoption of features important for the HPC community into the C++ standard.

This report documents the completion of milestone STPRO4-4 Kokkos back-ends research, collaborations, development, optimization, and documentation. The Kokkos team updated its existing backend to support the software stack and hardware of DOE's Sierra, Summit and Astra machines. They also collaborated with ECP PathForward vendors on developing backends for possible exa-scale architectures. Furthermore, the team ramped up its engagement with the ISO/C++ committee to accelerate the adoption of features important for the HPC community into the C++ standard.

This report documents the completion of milestone STPRO4-5 Kokkos interoperability with general SIMD types to force vectorization on ATS-1. The Kokkos team worked with application developers to enable the utilization of SIMD intrinsics, which allowed up to 3.7x improvement of the affected kernels on ATS-1 in a proxy application. SIMD types are now deployed in the production code base.

This report documents the completion of milestone STPRO4-6 Kokkos Support for ASC applications and libraries. The team provided consultation and support for numerous ASC code projects including Sandias SPARC, EMPIRE, Aria, GEMMA, Alexa, Trilinos, LAMMPS and nimbleSM. Over the year more than 350 Kokkos github issues were resolved, with over 220 requiring fixes and enhancements to the code base. Resolving these requests, with many of them issued by ASC code teams, provided applications with the necessary capabilities in Kokkos to be successful.

This report documents the completion of milestone STPRO4-7 Kokkos R&D: Remote Memory Spaces for One-Sided Halo-Exchange. The goal of this milestone was to develop and deploy an initial capability to support PGAS like communication models integrated into Kokkos via Remote Memory Spaces. The team developed semantic requirements for Remote Memory Spaces and implemented a prototype library leveraging four different communication libraries: libQUO, SHMEM, MPI-OneSided and NVSHMEM. In conjunction with ADCD02-COPA the Remote Memory Space capability was used in ExaMiniMD — a Molecular Dynamics Proxy Application — to explore the current state of the technology and its usability. The obtained results demonstrate that usability is very good, allowing a significant simplification communication routines, but performance is still lacking.

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This report documents the completion of milestone STPM12-4 Kokkos Training Bootcamp. The goal of this milestone was to hold a combined tutorial and hackathon bootcamp event for the Kokkos community and prospective users. The Kokkos Bootcamp event was held on-site at Oak Ridge National Lab from July 24 — July 27, 2018. There were over 40 registered participants from 12 institutions, including 7 Kokkos project staff from SNL, LANL, and ORNL. The event consisted of a roughly a two-day tutorial session including hands exercises, followed by 1.5 days of intensive porting work on codes that the participants brought explore, port, and optimize the use of Kokkos with the help of Kokkos project experts.

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