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Exercise 1: First Kokkos Program

In this exercise, you will write and compile your first Kokkos program. The goal is to get familiar with the compiling process.

Step 1: Simple Kokkos program

In exercise, open the file main.cpp, initialize and finalize Kokkos. Do not forget to include the header.

Add a call to the Kokkos::print_configuration function to print the configuration of Kokkos.

Step 2: Compile the program with the serial backend

Open the CMakeLists.txt file and check its content. In all this tutorial, Kokkos is included to your build with the /cmake/SetUpKokkos.cmake script, either as an external dependency, or as an inlined dependency. In the former, Kokkos has already been compiled and installed, and its install path is given to CMake with Kokkos_ROOT option. In the later, Kokkos sources are either already present as a Git submodule, or they are downloaded by the script using CMake FetchContent; in either case Kokkos sources are located in /vendor/kokkos and compiled along with the project, which means that Kokkos options must be passed at configuration time. If the option CMAKE_DISABLE_FIND_PACKAGE_Kokkos is ON, then no installed instance of Kokkos will be used, and only the inline build of Kokkos will take place. Conversely, if the option CMAKE_REQUIRE_FIND_PACKAGE_Kokkos is ON, then only an installed instance of Kokkos will be used.

Compile your program using the serial backend. You can use the following commands:

cd exercise
cmake -B build_serial
cmake --build build_serial

This would use build Kokkos along with your code. If you have already installed Kokkos in exercise 0, then you can use the following commands instead:

cd exercise
cmake -B build_serial \
    -DKokkos_ROOT=path/to/kokkos/serial/install
cmake --build build_serial

Run the program and check the output:

build_serial/exe01

Step 3: Compile the program with the OpenMP backend

Recompile your program using the OpenMP backend. You can use the following commands:

cmake -B build_openmp \
    -DKokkos_ENABLE_OPENMP=ON
cmake --build build_openmp

If you have already installed Kokkos in exercise 0, then you can use the following commands instead:

cd exercise
cmake -B build_openmp \
    -DKokkos_ROOT=path/to/kokkos/openmp/install
cmake --build build_openmp

Run the program and check the output:

build_openmp/exe01

For instance if you are on Linux and are using GCC, you should get something like this:

  Kokkos Version: 4.5.1
Compiler:
  KOKKOS_COMPILER_GNU: 1140
Architecture:
  CPU architecture: none
  Default Device: OpenMP
  GPU architecture: none
  platform: 64bit
Atomics:
Vectorization:
  KOKKOS_ENABLE_PRAGMA_IVDEP: no
  KOKKOS_ENABLE_PRAGMA_LOOPCOUNT: no
  KOKKOS_ENABLE_PRAGMA_UNROLL: no
  KOKKOS_ENABLE_PRAGMA_VECTOR: no
Memory:
Options:
  KOKKOS_ENABLE_ASM: yes
  KOKKOS_ENABLE_CXX17: yes
  KOKKOS_ENABLE_CXX20: no
  KOKKOS_ENABLE_CXX23: no
  KOKKOS_ENABLE_CXX26: no
  KOKKOS_ENABLE_DEBUG_BOUNDS_CHECK: no
  KOKKOS_ENABLE_HWLOC: no
  KOKKOS_ENABLE_LIBDL: yes
Host Parallel Execution Space:
  KOKKOS_ENABLE_OPENMP: yes

OpenMP Runtime Configuration:
Kokkos::OpenMP thread_pool_topology[ 1 x 20 x 1 ]

If you have an Apple computer and you are using the Clang compiler, you should get something like this instead:

  Kokkos Version: 4.4.0
Compiler:
  KOKKOS_COMPILER_APPLECC: 6000
Architecture:
  CPU architecture: none
  Default Device: N6Kokkos6OpenMPE
  GPU architecture: none
  platform: 64bit
Atomics:
Vectorization:
  KOKKOS_ENABLE_PRAGMA_IVDEP: no
  KOKKOS_ENABLE_PRAGMA_LOOPCOUNT: no
  KOKKOS_ENABLE_PRAGMA_UNROLL: no
  KOKKOS_ENABLE_PRAGMA_VECTOR: no
Memory:
Options:
  KOKKOS_ENABLE_ASM: no
  KOKKOS_ENABLE_CXX17: yes
  KOKKOS_ENABLE_CXX20: no
  KOKKOS_ENABLE_CXX23: no
  KOKKOS_ENABLE_CXX26: no
  KOKKOS_ENABLE_DEBUG_BOUNDS_CHECK: no
  KOKKOS_ENABLE_HWLOC: no
  KOKKOS_ENABLE_LIBDL: yes
Host Parallel Execution Space:
  KOKKOS_ENABLE_OPENMP: yes

OpenMP Runtime Configuration:
Kokkos::OpenMP thread_pool_topology[ 1 x 10 x 1 ]

Step 4: Compile the program with a Cuda/HIP/SYCL backend

Recompile your program now using the Cuda backend, by instance. You can use the following commands:

cd exercise
cmake -B build_cuda \
    -DKokkos_ENABLE_CUDA=ON \
    -DKokkos_ARCH_<ARCH>=ON
cmake --build build_cuda

Specify the architecture flag that applies.

If you have already installed Kokkos in exercise 0, then you can use the following commands instead:

cd exercise
cmake -B build_cuda \
    -DKokkos_ROOT=path/to/kokkos/cuda/install
cmake --build build_cuda

Run the program and check the output:

build_cuda/exe01

For instance if you are on Linux and are using GCC, you should get something like this on a computer with an A500 GPU:

  Kokkos Version: 4.5.1
Compiler:
  KOKKOS_COMPILER_GNU: 1140
  KOKKOS_COMPILER_NVCC: 1220
Architecture:
  CPU architecture: none
  Default Device: Cuda
  GPU architecture: AMPERE86
  platform: 64bit
Atomics:
Vectorization:
  KOKKOS_ENABLE_PRAGMA_IVDEP: no
  KOKKOS_ENABLE_PRAGMA_LOOPCOUNT: no
  KOKKOS_ENABLE_PRAGMA_UNROLL: no
  KOKKOS_ENABLE_PRAGMA_VECTOR: no
Memory:
Options:
  KOKKOS_ENABLE_ASM: yes
  KOKKOS_ENABLE_CXX17: yes
  KOKKOS_ENABLE_CXX20: no
  KOKKOS_ENABLE_CXX23: no
  KOKKOS_ENABLE_CXX26: no
  KOKKOS_ENABLE_DEBUG_BOUNDS_CHECK: no
  KOKKOS_ENABLE_HWLOC: no
  KOKKOS_ENABLE_LIBDL: yes
Host Serial Execution Space:
  KOKKOS_ENABLE_SERIAL: yes

Serial Runtime Configuration:
Device Execution Space:
  KOKKOS_ENABLE_CUDA: yes
Cuda Options:
  KOKKOS_ENABLE_CUDA_RELOCATABLE_DEVICE_CODE: no
  KOKKOS_ENABLE_CUDA_UVM: no
  KOKKOS_ENABLE_IMPL_CUDA_MALLOC_ASYNC: no

Cuda Runtime Configuration:
macro  KOKKOS_ENABLE_CUDA      : defined
macro  CUDA_VERSION          = 12020 = version 12.2
Kokkos::Cuda[ 0 ] NVIDIA RTX A500 Laptop GPU capability 8.6, Total Global Memory: 3.813 GiB, Shared Memory per Block: 48 KiB : Selected