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Kokkos Core implements a programming model in C++ for writing performance portable applications targeting all major HPC platforms. For that purpose it provides abstractions for both parallel execution of code and data management. Kokkos is designed to target complex node architectures with N-level memory hierarchies and multiple types of execution resources. It currently can use OpenMP, Pthreads and CUDA as backend programming models. Kokkos Core is part of the Kokkos C++ Performance Portability Programming EcoSystem, which also provides math kernels (https://github.com/kokkos/kokkos-kernels), as well as profiling and debugging tools (https://github.com/kokkos/kokkos-tools). # Learning about Kokkos A programming guide can be found on the Wiki, the API reference is under development. For questions find us on Slack: https://kokkosteam.slack.com or open a github issue. For non-public questions send an email to crtrott(at)sandia.gov A separate repository with extensive tutorial material can be found under https://github.com/kokkos/kokkos-tutorials. Furthermore, the 'example/tutorial' directory provides step by step tutorial examples which explain many of the features of Kokkos. They work with simple Makefiles. To build with g++ and OpenMP simply type 'make' in the 'example/tutorial' directory. This will build all examples in the subfolders. To change the build options refer to the Programming Guide in the compilation section. To learn more about Kokkos consider watching one of our presentations: * GTC 2015: - http://on-demand.gputechconf.com/gtc/2015/video/S5166.html - http://on-demand.gputechconf.com/gtc/2015/presentation/S5166-H-Carter-Edwards.pdf # Contributing to Kokkos We are open and try to encourage contributions from external developers. To do so please first open an issue describing the contribution and then issue a pull request against the develop branch. For larger features it may be good to get guidance from the core development team first through the github issue. Note that Kokkos Core is licensed under standard 3-clause BSD terms of use. Which means contributing to Kokkos allows anyone else to use your contributions not just for public purposes but also for closed source commercial projects. For specifics see the LICENSE file contained in the repository or distribution. # Requirements ### Primary tested compilers on X86 are: * GCC 4.8.4 * GCC 4.9.3 * GCC 5.1.0 * GCC 5.5.0 * GCC 6.1.0 * GCC 7.2.0 * GCC 7.3.0 * GCC 8.1.0 * Intel 15.0.2 * Intel 16.0.1 * Intel 17.0.1 * Intel 17.4.196 * Intel 18.2.128 * Clang 3.6.1 * Clang 3.7.1 * Clang 3.8.1 * Clang 3.9.0 * Clang 4.0.0 * Clang 6.0.0 for CUDA (CUDA Toolkit 9.0) * Clang 7.0.0 for CUDA (CUDA Toolkit 9.1) * PGI 18.7 * NVCC 7.5 for CUDA (with gcc 4.8.4) * NVCC 8.0.44 for CUDA (with gcc 5.3.0) * NVCC 9.1 for CUDA (with gcc 6.1.0) ### Primary tested compilers on Power 8 are: * GCC 6.4.0 (OpenMP,Serial) * GCC 7.2.0 (OpenMP,Serial) * IBM XL 16.1.0 (OpenMP, Serial) * NVCC 9.2.88 for CUDA (with gcc 7.2.0 and XL 16.1.0) ### Primary tested compilers on Intel KNL are: * Intel 16.4.258 (with gcc 4.7.2) * Intel 17.2.174 (with gcc 4.9.3) * Intel 18.2.199 (with gcc 4.9.3) ### Primary tested compilers on ARM (Cavium ThunderX2) * GCC 7.2.0 * ARM/Clang 18.4.0 ### Other compilers working: * X86: - Cygwin 2.1.0 64bit with gcc 4.9.3 - GCC 8.1.0 (not warning free) ### Known non-working combinations: * Power8: - Pthreads backend * ARM - Pthreads backend Primary tested compiler are passing in release mode with warnings as errors. They also are tested with a comprehensive set of backend combinations (i.e. OpenMP, Pthreads, Serial, OpenMP+Serial, ...). We are using the following set of flags: GCC: -Wall -Wshadow -pedantic -Werror -Wsign-compare -Wtype-limits -Wignored-qualifiers -Wempty-body -Wclobbered -Wuninitialized Intel: -Wall -Wshadow -pedantic -Werror -Wsign-compare -Wtype-limits -Wuninitialized Clang: -Wall -Wshadow -pedantic -Werror -Wsign-compare -Wtype-limits -Wuninitialized NVCC: -Wall -Wshadow -pedantic -Werror -Wsign-compare -Wtype-limits -Wuninitialized Other compilers are tested occasionally, in particular when pushing from develop to master branch, without -Werror and only for a select set of backends. # Running Unit Tests To run the unit tests create a build directory and run the following commands KOKKOS_PATH/generate_makefile.bash make build-test make test Run KOKKOS_PATH/generate_makefile.bash --help for more detailed options such as changing the device type for which to build. # Installing the library To install Kokkos as a library create a build directory and run the following KOKKOS_PATH/generate_makefile.bash --prefix=INSTALL_PATH make kokkoslib make install KOKKOS_PATH/generate_makefile.bash --help for more detailed options such as changing the device type for which to build. Note that in many cases it is preferable to build Kokkos inline with an application. The main reason is that you may otherwise need many different configurations of Kokkos installed depending on the required compile time features an application needs. For example there is only one default execution space, which means you need different installations to have OpenMP or Pthreads as the default space. Also for the CUDA backend there are certain choices, such as allowing relocatable device code, which must be made at installation time. Building Kokkos inline uses largely the same process as compiling an application against an installed Kokkos library. See for example benchmarks/bytes_and_flops/Makefile which can be used with an installed library and for an inline build. ### CMake Kokkos supports being build as part of a CMake applications. An example can be found in example/cmake_build. # Kokkos and CUDA UVM Kokkos does support UVM as a specific memory space called CudaUVMSpace. Allocations made with that space are accessible from host and device. You can tell Kokkos to use that as the default space for Cuda allocations. In either case UVM comes with a number of restrictions: (i) You can't access allocations on the host while a kernel is potentially running. This will lead to segfaults. To avoid that you either need to call Kokkos::Cuda::fence() (or just Kokkos::fence()), after kernels, or you can set the environment variable CUDA_LAUNCH_BLOCKING=1. Furthermore in multi socket multi GPU machines without NVLINK, UVM defaults to using zero copy allocations for technical reasons related to using multiple GPUs from the same process. If an executable doesn't do that (e.g. each MPI rank of an application uses a single GPU [can be the same GPU for multiple MPI ranks]) you can set CUDA_MANAGED_FORCE_DEVICE_ALLOC=1. This will enforce proper UVM allocations, but can lead to errors if more than a single GPU is used by a single process. # Citing Kokkos If you publish work which mentions Kokkos, please cite the following paper: @article{CarterEdwards20143202, title = "Kokkos: Enabling manycore performance portability through polymorphic memory access patterns ", journal = "Journal of Parallel and Distributed Computing ", volume = "74", number = "12", pages = "3202 - 3216", year = "2014", note = "Domain-Specific Languages and High-Level Frameworks for High-Performance Computing ", issn = "0743-7315", doi = "https://doi.org/10.1016/j.jpdc.2014.07.003", url = "http://www.sciencedirect.com/science/article/pii/S0743731514001257", author = "H. Carter Edwards and Christian R. Trott and Daniel Sunderland" }