Kokkos

Kokkos

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 Serial and OpenMP (threads) for CPU execution spaces ("backends") and CUDA, HIP, SYCL, and OpenMPTarget for GPU execution spaces. By convention, Kokkos only allows one GPU backend at a time.

Kokkos Documentation

• Kokkos-core Wiki
• Kokkos github

Kokkos on Polaris

The prebuilt Kokkos on polaris includes 3 backends: Serial and OpenMP for CPU execution and CUDA for GPU execution. To use it, run

module use /soft/modulefiles
module swap PrgEnv-nvhpc PrgEnv-gnu
module swap gcc/12.2.0 gcc/11.2.0
module load cudatoolkit-standalone/11.8.0
module load kokkos

(Since the SlingShot 11 upgrade, you must use PrgEnv-gnu and the gcc and cudatoolkit version changes indicated, at least until some subsequent Polaris sytem updates have been completed.)

This sets the following environment variables, some of which are used by cmake:

• KOKKOS_HOME - path to the lib64/, include/ files installed
• LIBRARY_PATH - prepends $KOKKOS_HOME/lib64 to this variable used by cmake
• CPATH - prepends $KOKKOS_HOME/include to this variable used by cmake
• LD_LIBRARY_PATH - prepends $KOKKOS_HOME/lib64 to this variable

Building a Kokkos Application Using cmake

Add these lines to CMakeLists.txt:

find_package(Kokkos REQUIRED)
target_link_libraries(myTarget Kokkos::kokkoscore)

Here is a simple example CMakeLists.txt to compile an example program:

cmake_minimum_required(VERSION 3.22)
project(buildExample)
find_package(Kokkos REQUIRED)

set(buildExample_SOURCE_DIR ".")

set(top_SRCS
  ${buildExample_SOURCE_DIR}/example1.cpp)

set(SOURCE_FILES ${top_SRCS})

add_executable(example1_sycl_aot ${SOURCE_FILES})
target_link_libraries(example1_sycl_aot Kokkos::kokkoscore)
target_include_directories(example1_sycl_aot PUBLIC ${buildExample_SOURCE_DIR})

Configure and build it like this:

mkdir build
cd build
cmake -DCMAKE_CXX_COMPILER=CC -DCMAKE_C_COMPILER=cc ..
make

Building a Kokkos Application Using make

Here's an example Makefile:

# KOKKOS_HOME set via:
#   module load kokkos

# You can look at the first lines of $KOKKOS_HOME/KokkosConfigCommon.cmake to
# see the flags used in cmake configuration of the kokkos library build. The
# default Kokkos module on Polaris was built with PrgEnv-nvhpc and includes
# Serial, OpenMP (threads) and CUDA backends. So you should have that
# environment module loaded and include compiler flags for cuda and openmp:

# Cray MPI wrapper for C++ and C compilers:
CXX=CC
CC=cc

CPPFLAGS=-cuda -fopenmp
LDFLAGS=

LDFLAGS=$(CPPFLAGS) $(LDFLAGS)
LDLIBS=-L$(KOKKOS_HOME)/lib64 -lkokkoscore -lkokkossimd -lpthread

SRCS=example1.cpp
OBJS=$(subst .cpp,.o,$(SRCS))

all: example1_polaris

example1_polaris: $(OBJS)
        $(CXX) $(LDFLAGS) -o example1_polaris $(OBJS) $(LDLIBS)

example1.o: example1.cpp

clean:
        rm -f $(OBJS)

distclean: clean
        rm -f example1_polaris

Configuring Your Own Kokkos Build on Polaris

Here are recommended environment settings and configuration to build your own kokkos libraries on Polaris:

Environment

To match what was done in the centrally-built kokkos associated with the modules discussed above, use the programming environment PrgEnv-gnu, and use the Cray wrapper CC as the C++ compiler. You'll also need to back up from the default gcc compiler version and make a few other module adjustments to work correctly on Polaris following the SlingShot 11 upgrade (and prior to some planned system upgrades that will make some of this environment tweaking unnecessary):

module load cmake
module swap PrgEnv-nvhpc PrgEnv-gnu
module swap gcc/12.2.0 gcc/11.2.0
module load cudatoolkit-standalone/11.8.0

CMake Configuration

This example builds three backends: OpenMP, Serial, and Cuda.

git clone [email protected]:kokkos/kokkos.git
cd kokkos
mkdir build
cd build

cmake\
 -DCMAKE_BUILD_TYPE=RelWithDebInfo\
 -DCMAKE_INSTALL_PREFIX="./install"\
 -DCMAKE_CXX_COMPILER=CC\
 -DKokkos_ENABLE_OPENMP=ON\
 -DKokkos_ENABLE_SERIAL=ON\
 -DKokkos_ARCH_ZEN3=ON\
 -DKokkos_ARCH_AMPERE80=ON\
 -DKokkos_ENABLE_CUDA=ON\
 -DKokkos_ENABLE_AGGRESSIVE_VECTORIZATION=ON\
 -DKokkos_ENABLE_TESTS=OFF\
 -DBUILD_TESTING=OFF\
 -DKokkos_ENABLE_CUDA_LAMBDA=ON\
 -DKokkos_ENABLE_IMPL_DESUL_ATOMICS=OFF\
 -DCMAKE_CXX_STANDARD=17\
 -DCMAKE_EXE_LINKER_FLAGS=-no-gcc-rpath\
 ..

make -j16 -l16 install

(The -no-gcc-rpath linker flag is to work around a bug in the post-SlingShot11 compiler environment on Polaris.)