This repository contains an initial low-level API library for the efficient high-order discretization methods developed by the ECP co-design Center for Efficient Exascale Discretizations (CEED). While our focus is on high-order finite elements, the approach is mostly algebraic and thus applicable to other discretizations in factored form, as explained in the API documentation portion of the Doxygen documentation.
One of the challenges with high-order methods is that a global sparse matrix is no longer a good representation of a high-order linear operator, both with respect to the FLOPs needed for its evaluation, as well as the memory transfer needed for a matvec. Thus, high-order methods require a new "format" that still represents a linear (or more generally non-linear) operator, but not through a sparse matrix.
The goal of libCEED is to propose such a format, as well as supporting implementations and data structures, that enable efficient operator evaluation on a variety of computational device types (CPUs, GPUs, etc.). This new operator description is based on algebraically factored form, which is easy to incorporate in a wide variety of applications, without significant refactoring of their own discretization infrastructure.
The repository is part of the CEED software suite, a collection of software benchmarks, miniapps, libraries and APIs for efficient exascale discretizations based on high-order finite element and spectral element methods. See http://github.com/ceed for more information and source code availability.
The CEED research is supported by the Exascale Computing Project (17-SC-20-SC), a collaborative effort of two U.S. Department of Energy organizations (Office of Science and the National Nuclear Security Administration) responsible for the planning and preparation of a capable exascale ecosystem, including software, applications, hardware, advanced system engineering and early testbed platforms, in support of the nation’s exascale computing imperative.
For more details on the CEED API see http://ceed.exascaleproject.org/ceed-code/.
The CEED library, libceed, is a C99 library with no external dependencies. It
can be built using
make
or, with optimization flags
make OPT='-O3 -march=skylake-avx512 -ffp-contract=fast'
These optimization flags are used by all languages (C, C++, Fortran) and this makefile variable can also be set for testing and examples (below).
The test suite produces TAP output and is run by:
make test
or, using the prove tool distributed with Perl (recommended)
make prove
libCEED comes with several examples of its usage, ranging from standalone C
codes in the /examples/ceed directory to examples based on external packages,
such as MFEM, PETSc and Nek5000.
To build the examples, set the MFEM_DIR, PETSC_DIR and NEK5K_DIR variables
and run:
# libCEED examples on CPU and GPU
cd examples/ceed
make
./ex1 -ceed /cpu/self
./ex1 -ceed /gpu/occa
cd ../..
# MFEM+libCEED examples on CPU and GPU
cd examples/mfem
make
./bp1 -ceed /cpu/self -no-vis
./bp1 -ceed /gpu/occa -no-vis
cd ../..
# PETSc+libCEED examples on CPU and GPU
cd examples/petsc
make
./bp1 -ceed /cpu/self
./bp1 -ceed /gpu/occa
cd ../..
# Nek+libCEED examples on CPU and GPU
cd examples/nek5000
./make-nek-examples.sh
./run-nek-example.sh -ceed /cpu/self -b 3
./run-nek-example.sh -ceed /gpu/occa -b 3
cd ../..The above code assumes a GPU-capable machine enabled in the OCCA
backend. Depending on the available backends, other Ceed resource specifiers can
be provided with the -ceed option, for example:
CEED resource (-ceed) |
Backend |
|---|---|
/cpu/self/blocked |
Serial blocked implementation |
/cpu/self/ref |
Serial reference implementation |
/cpu/self/tmpl |
Backend template, dispatches to /cpu/self/blocked |
/cpu/occa |
Serial OCCA kernels |
/gpu/occa |
CUDA OCCA kernels |
/omp/occa |
OpenMP OCCA kernels |
/ocl/occa |
OpenCL OCCA kernels |
/gpu/magma |
CUDA MAGMA kernels |
To install libCEED, run
make install prefix=/usr/local
or (e.g., if creating packages),
make install prefix=/usr DESTDIR=/packaging/path
Note that along with the library, libCEED installs kernel sources, e.g. OCCA
kernels are installed in $prefix/lib/okl. This allows the OCCA backend to
build specialized kernels at run-time. In a normal setting, the kernel sources
will be found automatically (relative to the library file libceed.so).
However, if that fails (e.g. if libceed.so is moved), one can copy (cache) the
kernel sources inside the user OCCA directory, ~/.occa using
$(OCCA_DIR)/bin/occa cache ceed $(CEED_DIR)/lib/okl/*.okl
This will allow OCCA to find the sources regardless of the location of the CEED
library. One may occasionally need to clear the OCCA cache, which can be accomplished
by removing the ~/.occa directory or by calling $(OCCA_DIR)/bin/occa clear -a.
In addition to library and header, libCEED provides a pkg-config
file that can be used to easily compile and link. For example, if
$prefix is a standard location or you set the environment variable
PKG_CONFIG_PATH,
cc `pkg-config --cflags --libs ceed` -o myapp myapp.c
will build myapp with libCEED. This can be used with the source or
installed directories. Most build systems have support for pkg-config.
You can reach the libCEED team by emailing [email protected] or by leaving a comment in the issue tracker.
The following copyright applies to each file in the CEED software suite, unless otherwise stated in the file:
Copyright (c) 2017, Lawrence Livermore National Security, LLC. Produced at the Lawrence Livermore National Laboratory. LLNL-CODE-734707. All Rights reserved.
See files LICENSE and NOTICE for details.