Grid

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Data parallel C++ mathematical object library.

Please send all pull requests to the develop branch.

License: GPL v2.

Last update 2016/08/03.

Description

This library provides data parallel C++ container classes with internal memory layout that is transformed to map efficiently to SIMD architectures. CSHIFT facilities are provided, similar to HPF and cmfortran, and user control is given over the mapping of array indices to both MPI tasks and SIMD processing elements.

• Identically shaped arrays then be processed with perfect data parallelisation.
• Such identically shapped arrays are called conformable arrays.

The transformation is based on the observation that Cartesian array processing involves identical processing to be performed on different regions of the Cartesian array.

The library will both geometrically decompose into MPI tasks and across SIMD lanes. Local vector loops are parallelised with OpenMP pragmas.

Data parallel array operations can then be specified with a SINGLE data parallel paradigm, but optimally use MPI, OpenMP and SIMD parallelism under the hood. This is a significant simplification for most programmers.

The layout transformations are parametrised by the SIMD vector length. This adapts according to the architecture. Presently SSE4 (128 bit) AVX, AVX2 (256 bit) and IMCI and AVX512 (512 bit) targets are supported (ARM NEON and BG/Q QPX on the way).

These are presented as vRealF, vRealD, vComplexF, and vComplexD internal vector data types. These may be useful in themselves for other programmers. The corresponding scalar types are named RealF, RealD, ComplexF and ComplexD.

MPI, OpenMP, and SIMD parallelism are present in the library. Please see https://arxiv.org/abs/1512.03487 for more detail.

Installation

First, start by cloning the repository:

git clone https://github.com/paboyle/Grid.git

Then enter the cloned directory and set up the build system:

cd Grid
./bootstrap.sh

Now you can execute the configure script to generate makefiles (here from a build directory):

mkdir build; cd build
../configure --enable-precision=double --enable-simd=AVX --enable-comms=mpi-auto --prefix=<path>

where --enable-precision= set the default precision (single or double), --enable-simd= set the SIMD type (see possible values below), --enable- comms= set the protocol used for communications (none, mpi, mpi-auto or shmem), and <path> should be replaced by the prefix path where you want to install Grid. The mpi-auto communication option set configure to determine automatically how to link to MPI. Other options are available, use configure --help to display them. Like with any other program using GNU autotool, the CXX, CXXFLAGS, LDFLAGS, ... environment variables can be modified to customise the build.

Finally, you can build and install Grid:

make; make install

To minimise the build time, only the tests at the root of the tests directory are built by default. If you want to build tests in the sub-directory <subdir> you can execute:

make -C tests/<subdir> tests

Possible SIMD types

The following options can be use with the --enable-simd= option to target different SIMD instruction sets:

String	Description
GEN	generic portable vector code
SSE4	SSE 4.2 (128 bit)
AVX	AVX (256 bit)
AVXFMA4	AVX (256 bit) + FMA
AVX2	AVX 2 (256 bit)
AVX512	AVX 512 bit
AVX512MIC	AVX 512 bit for Intel MIC architecture
ICMI	Intel ICMI instructions (512 bit)

Alternatively, some CPU codenames can be directly used:

String	Description
KNC	Intel Knights Corner
KNL	Intel Knights Landing