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 Aurora

The prebuilt Kokkos on Aurora includes 3 backends: Serial and OpenMP for CPU execution and SYCL for GPU execution (with ahead-of-time (AOT) compilation, not just-in-time (JIT) compilation). To use it, run

module load kokkos

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

• KOKKOS_ROOT - path to the lib64/, include/ files installed
• LIBRARY_PATH - prepends $KOKKOS_ROOT/lib64 to this variable used by cmake
• CPATH - prepends $KOKKOS_ROOT/include to this variable used by cmake
• LD_LIBRARY_PATH - prepends $KOKKOS_ROOT/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_ROOT set via:
#   module load kokkos
# 
# You can look at the first lines of
# $KOKKOS_ROOT/lib64/cmake/Kokkos/KokkosConfigCommon.cmake to see the flags
# used in cmake configuration of the kokkos library build. The default Kokkos
# module on Aurora was built with the default oneAPI module and includes
# Serial, OpenMP (threads) and SYCL backends. So you should have that
# environment module loaded and include compiler flags for sycl and openmp:

# Aurora MPICH wrapper for C++ and C compilers:
CXX="mpic++ -cxx=icpx"
CC="mpicc -cc=icx"

SYCL_AOT_CPPFLAGS=-fsycl -fsycl-targets=spir64_gen -fno-sycl-id-queries-fit-in-int -fsycl-dead-args-optimization -fsycl-unnamed-lambda -std=c++17
SYCL_AOT_LDFLAGS=-Xsycl-target-backend "-device pvc"

CPPFLAGS=-g -O2 -fiopenmp -I $(KOKKOS_ROOT)/include $(SYCL_AOT_CPPFLAGS) -Wno-deprecated-declarations -Wno-tautological-constant-compare -Wno-unknown-attributes -ffp-model=precise

LDFLAGS=$(CPPFLAGS) $(SYCL_AOT_LDFLAGS)
LDLIBS=-L$(KOKKOS_ROOT)/lib64 -lkokkoscore -lkokkossimd -lkokkoscontainers -lpthread

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

all: example1_aurora

example1_aurora: $(OBJS)
        $(CXX) $(LDFLAGS) -o example1_aurora $(OBJS) $(LDLIBS)

example1.o: example1.cpp

clean:
        rm -f $(OBJS)

distclean: clean
        rm -f example1_aurora

Configuring Your Own Kokkos Build on Aurora

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

Environment

To match what was done in the centrally-built kokkos associated with the modules discussed above, use the same oneAPI version as indicated in module help kokkos and use the Aurora MPICH wrapper mpic++ -cxx=icpx as the C++ compiler (or just use icpx if you're not using MPI). To build Kokkos, you'll need cmake.

CMake Configuration

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

git clone git@github.com:kokkos/kokkos.git
cd kokkos
mkdir build
cd build

cmake\
    -DCMAKE_BUILD_TYPE=RelWithDebInfo\
    -DCMAKE_CXX_COMPILER=icpx\
    -DCMAKE_CXX_EXTENSIONS=OFF\
    -DCMAKE_CXX_STANDARD=17\
    -DKokkos_ENABLE_TESTS=OFF\
    -DKokkos_ENABLE_SERIAL=ON\
    -DKokkos_ENABLE_OPENMP=ON\
    -DKokkos_ENABLE_SYCL=ON\
    -DKokkos_ARCH_INTEL_GEN=ON\
    -DKokkos_ENABLE_SYCL_RELOCATABLE_DEVICE_CODE=OFF\
    -DKokkos_ENABLE_IMPL_SYCL_DEVICE_GLOBAL_SUPPORTED=OFF\
    -DBUILD_SHARED_LIBS=ON\
    -DKokkos_ENABLE_DEPRECATED_CODE_3=ON\
    -DKokkos_ENABLE_DEBUG=OFF\
    -DKokkos_ENABLE_EXAMPLES=OFF\
    -DCMAKE_CXX_FLAGS="-Wno-deprecated-declarations -Wno-tautological-constant-compare -ffp-model=precise -Xsycl-target-backend \"-device pvc\""\
    -DCMAKE_EXE_LINKER_FLAGS="-ffp-model=precise -fsycl-max-parallel-link-jobs=20 -fno-sycl-rdc"\
    -DCMAKE_VERBOSE_MAKEFILE=OFF\
    -DCMAKE_INSTALL_PREFIX=/path/to/your/install/directory\
    ..

make -j16 -l16 install