1# libCEED: the CEED API Library 2 3[](https://travis-ci.org/CEED/libCEED) 4[](https://codecov.io/gh/CEED/libCEED/) 5[](https://opensource.org/licenses/BSD-2-Clause) 6[](https://codedocs.xyz/CEED/libCEED/) 7 8## Code for Efficient Extensible Discretization 9 10This repository contains an initial low-level API library for the efficient 11high-order discretization methods developed by the ECP co-design [Center for 12Efficient Exascale Discretizations (CEED)](http://ceed.exascaleproject.org). 13While our focus is on high-order finite elements, the approach is mostly 14algebraic and thus applicable to other discretizations in factored form, as 15explained in the API documentation portion of the [Doxygen documentation](https://codedocs.xyz/CEED/libCEED/md_doc_libCEEDapi.html). 16 17One of the challenges with high-order methods is that a global sparse matrix is 18no longer a good representation of a high-order linear operator, both with 19respect to the FLOPs needed for its evaluation, as well as the memory transfer 20needed for a matvec. Thus, high-order methods require a new "format" that still 21represents a linear (or more generally non-linear) operator, but not through a 22sparse matrix. 23 24The goal of libCEED is to propose such a format, as well as supporting 25implementations and data structures, that enable efficient operator evaluation 26on a variety of computational device types (CPUs, GPUs, etc.). This new operator 27description is based on algebraically [factored form](https://codedocs.xyz/CEED/libCEED/md_doc_libCEEDapi.html), 28which is easy to incorporate in a wide variety of applications, without significant 29refactoring of their own discretization infrastructure. 30 31The repository is part of the [CEED software suite][ceed-soft], a collection of 32software benchmarks, miniapps, libraries and APIs for efficient exascale 33discretizations based on high-order finite element and spectral element methods. 34See http://github.com/ceed for more information and source code availability. 35 36The CEED research is supported by the [Exascale Computing Project][ecp] 37(17-SC-20-SC), a collaborative effort of two U.S. Department of Energy 38organizations (Office of Science and the National Nuclear Security 39Administration) responsible for the planning and preparation of a [capable 40exascale ecosystem](https://exascaleproject.org/what-is-exascale), including 41software, applications, hardware, advanced system engineering and early testbed 42platforms, in support of the nation’s exascale computing imperative. 43 44For more details on the CEED API see http://ceed.exascaleproject.org/ceed-code/. 45 46## Building 47 48The CEED library, `libceed`, is a C99 library with no external dependencies. It 49can be built using 50 51 make 52 53or, with optimization flags 54 55 make OPT='-O3 -march=skylake-avx512 -ffp-contract=fast' 56 57These optimization flags are used by all languages (C, C++, Fortran) and this 58makefile variable can also be set for testing and examples (below). 59 60The library attempts to automatically detect support for the AVX 61instruction set using gcc-style compiler options for the host. 62Support may need to be manually specified via 63 64 make AVX=1 65 66or 67 68 make AVX=0 69 70if your compiler does not support gcc-style options, if you are cross 71compiling, etc. 72 73## Testing 74 75The test suite produces [TAP](https://testanything.org) output and is run by: 76 77 make test 78 79or, using the `prove` tool distributed with Perl (recommended) 80 81 make prove 82 83## Backends 84 85There are multiple supported backends, which can be selected at runtime in the examples: 86 87| CEED resource | Backend | 88| :----------------------- | :------------------------------------------------ | 89| `/cpu/self/ref/serial` | Serial reference implementation | 90| `/cpu/self/ref/blocked` | Blocked refrence implementation | 91| `/cpu/self/tmpl` | Backend template, delegates to `/cpu/self/ref/blocked` | 92| `/cpu/self/ref/memcheck` | Memcheck backend, undefined value checks | 93| `/cpu/self/avx/serial` | Serial AVX implementation | 94| `/cpu/self/avx/blocked` | Blocked AVX implementation | 95| `/cpu/self/xsmm/serial` | Serial LIBXSMM implementation | 96| `/cpu/self/xsmm/blocked` | Blocked LIBXSMM implementation | 97| `/cpu/occa` | Serial OCCA kernels | 98| `/gpu/occa` | CUDA OCCA kernels | 99| `/omp/occa` | OpenMP OCCA kernels | 100| `/ocl/occa` | OpenCL OCCA kernels | 101| `/gpu/cuda/ref` | Reference pure CUDA kernels | 102| `/gpu/cuda/reg` | Pure CUDA kernels using one thread per element | 103| `/gpu/cuda/shared | Optimized pure CUDA kernels using shared memory | 104| `/gpu/magma` | CUDA MAGMA kernels | 105 106 107The `/cpu/self/*/serial` backends process one element at a time and are intended for meshes 108with a smaller number of high order elements. The `/cpu/self/*/blocked` backends process 109blocked batches of eight interlaced elements and are intended for meshes with higher numbers 110of elements. 111 112The `/cpu/self/ref/*` backends are written in pure C and provide basic functionality. 113 114The `/cpu/self/avx/*` backends rely upon AVX instructions to provide vectorized CPU performance. 115 116The `/cpu/self/xsmm/*` backends rely upon the [LIBXSMM](http://github.com/hfp/libxsmm) package 117to provide vectorized CPU performance. The LIBXSMM backend does not use BLAS or MKL; however, 118if LIBXSMM was linked to MKL, this can be specified with the compilation flag `MKL=1`. 119 120The `/cpu/self/ref/memcheck` backend relies upon the [Valgrind](http://valgrind.org/) Memcheck tool 121to help verify that user QFunctions have no undefined values. To use, run your code with 122Valgrind and the Memcheck backend, e.g. `valgrind ./build/ex1 -ceed /cpu/self/ref/memcheck`. 123 124The `/*/occa` backends rely upon the [OCCA](http://github.com/libocca/occa) package to provide 125cross platform performance. 126 127The `/gpu/cuda/*` backends provide GPU performance strictly using CUDA. 128 129The `/gpu/magma` backend relies upon the [MAGMA](https://bitbucket.org/icl/magma) package. 130 131## Examples 132 133libCEED comes with several examples of its usage, ranging from standalone C 134codes in the `/examples/ceed` directory to examples based on external packages, 135such as MFEM, PETSc, and Nek5000. Nek5000 v18.0 or greater is required. 136 137To build the examples, set the `MFEM_DIR`, `PETSC_DIR` and `NEK5K_DIR` variables 138and run: 139 140```console 141# libCEED examples on CPU and GPU 142cd examples/ceed 143make 144./ex1 -ceed /cpu/self 145./ex1 -ceed /gpu/occa 146cd ../.. 147 148# MFEM+libCEED examples on CPU and GPU 149cd examples/mfem 150make 151./bp1 -ceed /cpu/self -no-vis 152./bp1 -ceed /gpu/occa -no-vis 153cd ../.. 154 155# PETSc+libCEED examples on CPU and GPU 156cd examples/petsc 157make 158./bp1 -ceed /cpu/self 159./bp1 -ceed /gpu/occa 160cd ../.. 161 162cd navier-stokes 163make 164./navierstokes -ceed /cpu/self 165./navierstokes -ceed /gpu/occa 166cd ../.. 167 168# Nek+libCEED examples on CPU and GPU 169cd examples/nek5000 170./make-nek-examples.sh 171./run-nek-example.sh -ceed /cpu/self -b 3 172./run-nek-example.sh -ceed /gpu/occa -b 3 173cd ../.. 174``` 175 176The above code assumes a GPU-capable machine with the OCCA backend 177enabled. Depending on the available backends, other Ceed resource specifiers can 178be provided with the `-ceed` option. 179 180## Benchmarks 181 182A sequence of benchmarks for all enabled backends can be run using 183 184```console 185make benchmarks 186``` 187 188The results from the benchmarks are stored inside the `benchmarks/` directory 189and they can be viewed using the commands (requires python with matplotlib): 190 191```console 192cd benchmarks 193python postprocess-plot.py petsc-bp1-*-output.txt 194python postprocess-plot.py petsc-bp3-*-output.txt 195``` 196 197Using the `benchmarks` target runs a comprehensive set of benchmarks which may 198take some time to run. Subsets of the benchmarks can be run using targets such 199as `make bench-petsc-bp1`, or `make bench-petsc-bp3`. 200 201For more details about the benchmarks, see 202[`benchmarks/README.md`](benchmarks/README.md) 203 204 205## Install 206 207To install libCEED, run 208 209 make install prefix=/usr/local 210 211or (e.g., if creating packages), 212 213 make install prefix=/usr DESTDIR=/packaging/path 214 215Note that along with the library, libCEED installs kernel sources, e.g. OCCA 216kernels are installed in `$prefix/lib/okl`. This allows the OCCA backend to 217build specialized kernels at run-time. In a normal setting, the kernel sources 218will be found automatically (relative to the library file `libceed.so`). 219However, if that fails (e.g. if `libceed.so` is moved), one can copy (cache) the 220kernel sources inside the user OCCA directory, `~/.occa` using 221 222 $(OCCA_DIR)/bin/occa cache ceed $(CEED_DIR)/lib/okl/*.okl 223 224This will allow OCCA to find the sources regardless of the location of the CEED 225library. One may occasionally need to clear the OCCA cache, which can be accomplished 226by removing the `~/.occa` directory or by calling `$(OCCA_DIR)/bin/occa clear -a`. 227 228### pkg-config 229 230In addition to library and header, libCEED provides a [pkg-config][pkg-config1] 231file that can be used to easily compile and link. [For example][pkg-config2], if 232`$prefix` is a standard location or you set the environment variable 233`PKG_CONFIG_PATH`, 234 235 cc `pkg-config --cflags --libs ceed` -o myapp myapp.c 236 237will build `myapp` with libCEED. This can be used with the source or 238installed directories. Most build systems have support for pkg-config. 239 240## Contact 241 242You can reach the libCEED team by emailing [ceed-users@llnl.gov](mailto:ceed-users@llnl.gov) 243or by leaving a comment in the [issue tracker](https://github.com/CEED/libCEED/issues). 244 245## Copyright 246 247The following copyright applies to each file in the CEED software suite, unless 248otherwise stated in the file: 249 250> Copyright (c) 2017, Lawrence Livermore National Security, LLC. Produced at the 251> Lawrence Livermore National Laboratory. LLNL-CODE-734707. All Rights reserved. 252 253See files LICENSE and NOTICE for details. 254 255[ceed-soft]: http://ceed.exascaleproject.org/software/ 256[ecp]: https://exascaleproject.org/exascale-computing-project 257[pkg-config1]: https://en.wikipedia.org/wiki/Pkg-config 258[pkg-config2]: https://people.freedesktop.org/~dbn/pkg-config-guide.html#faq 259
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