src/gromacs/ewald/pme_gpu_types.h

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  35
  36 /*! \internal \file
  37  * \brief Defines the PME GPU data structures
  38  * (the GPU function parameters used both on host and device sides).
  39  *
  40  * \author Aleksei Iupinov <a.yupinov@gmail.com>
  41  * \ingroup module_ewald
  42  */
  43
  44 #ifndef GMX_EWALD_PME_GPU_TYPES_H
  45 #define GMX_EWALD_PME_GPU_TYPES_H
  46
  47 /*
  48  * In OpenCL, the structures must be laid out on the host and device exactly the same way.
  49  * If something is off, one might get an error CL_INVALID_ARG_SIZE if any structure's sizes don't
  50  * match. What's worse, structures might be of same size but members might be aligned differently,
  51  * resulting in wrong kernel results. The structures below are aligned manually.
  52  * The pattern is ordering the members of structs from smallest to largest sizeof
  53  * (arrays behave the same way as sequences of separate fields),
  54  * as described in "The Lost Art of C Structure Packing".
  55  *
  56  * However, if the need arises at some point, they can all be aligned forcefully:
  57  *
  58  * #define GMX_GPU_ALIGNED __attribute__ ((aligned(8)))
  59  * struct GMX_GPU_ALIGNED PmeGpuConstParams
  60  * struct GMX_GPU_ALIGNED PmeGpuGridParams
  61  * etc...
  62  *
  63  * One might also try __attribute__ ((packed)), but it doesn't work with DeviceBuffer,
  64  * as it appears to not be POD.
  65  */
  66
  67
  68 /*! \brief A workaround to hide DeviceBuffer template from OpenCL kernel compilation
  69  * - to turn it into a dummy of the same size as host implementation of device buffer.
  70  * As we only care about 64-bit, 8 bytes is fine.
  71  * TODO: what we should be doing is providing separate device-side views of the same structures -
  72  * then there would be no need for macro.
  73  */
  74 #ifndef __OPENCL_C_VERSION__
  75 #    include "gromacs/gpu_utils/devicebuffer.h"
  76 #    define HIDE_FROM_OPENCL_COMPILER(x) x
  77 static_assert(sizeof(DeviceBuffer<float>) == 8,
  78               "DeviceBuffer is defined as an 8 byte stub for OpenCL C");
  79 static_assert(sizeof(DeviceBuffer<int>) == 8,
  80               "DeviceBuffer is defined as an 8 byte stub for OpenCL C");
  81 #else
  82 #    define HIDE_FROM_OPENCL_COMPILER(x) char8
  83 #endif
  84
  85 /* What follows is all the PME GPU function arguments,
  86  * sorted into several device-side structures depending on the update rate.
  87  * This is GPU agnostic (float3 replaced by float[3], etc.).
  88  * The GPU-framework specifics (e.g. cudaTextureObject_t handles) are described
  89  * in the larger structure PmeGpuCudaKernelParams in the pme.cuh.
  90  */
  91
  92 /*! \internal \brief
  93  * A GPU data structure for storing the constant PME data.
  94  * This only has to be initialized once.
  95  */
  96 struct PmeGpuConstParams
  97 {
  98     /*! \brief Electrostatics coefficient = ONE_4PI_EPS0 / pme->epsilon_r */
  99     float elFactor;
 100     /*! \brief Virial and energy GPU array. Size is c_virialAndEnergyCount (7) floats.
 101      * The element order is virxx, viryy, virzz, virxy, virxz, viryz, energy. */
 102     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_virialAndEnergy;
 103 };
 104
 105 /*! \internal \brief
 106  * A GPU data structure for storing the PME data related to the grid sizes and cut-off.
 107  * This only has to be updated at every DD step.
 108  */
 109 struct PmeGpuGridParams
 110 {
 111     /*! \brief Ewald solving factor = (M_PI / pme->ewaldcoeff_q)^2 */
 112     float ewaldFactor;
 113
 114     /* Grid sizes */
 115     /*! \brief Real-space grid data dimensions. */
 116     int realGridSize[DIM];
 117     /*! \brief Real-space grid dimensions, only converted to floating point. */
 118     float realGridSizeFP[DIM];
 119     /*! \brief Real-space grid dimensions (padded). The padding as compared to realGridSize includes the (order - 1) overlap. */
 120     int realGridSizePadded[DIM]; /* Is major dimension of this ever used in kernels? */
 121     /*! \brief Fourier grid dimensions. This counts the complex numbers! */
 122     int complexGridSize[DIM];
 123     /*! \brief Fourier grid dimensions (padded). This counts the complex numbers! */
 124     int complexGridSizePadded[DIM];
 125
 126     /*! \brief Offsets for X/Y/Z components of d_splineModuli */
 127     int splineValuesOffset[DIM];
 128     /*! \brief Offsets for X/Y/Z components of d_fractShiftsTable and d_gridlineIndicesTable */
 129     int tablesOffsets[DIM];
 130
 131     /* Grid arrays */
 132     /*! \brief Real space grid. */
 133     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_realGrid;
 134     /*! \brief Complex grid - used in FFT/solve. If inplace cu/clFFT is used, then it is the same handle as realGrid. */
 135     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_fourierGrid;
 136
 137     /*! \brief Grid spline values as in pme->bsp_mod
 138      * (laid out sequentially (XXX....XYYY......YZZZ.....Z))
 139      */
 140     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_splineModuli;
 141     /*! \brief Fractional shifts lookup table as in pme->fshx/fshy/fshz, laid out sequentially (XXX....XYYY......YZZZ.....Z) */
 142     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_fractShiftsTable;
 143     /*! \brief Gridline indices lookup table
 144      * (modulo lookup table as in pme->nnx/nny/nnz, laid out sequentially (XXX....XYYY......YZZZ.....Z)) */
 145     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<int>) d_gridlineIndicesTable;
 146 };
 147
 148 /*! \internal \brief
 149  * A GPU data structure for storing the PME data of the atoms, local to this process' domain
 150  * partition. This only has to be updated every DD step.
 151  */
 152 struct PmeGpuAtomParams
 153 {
 154     /*! \brief Number of local atoms */
 155     int nAtoms;
 156     /*! \brief Global GPU memory array handle with input rvec atom coordinates.
 157      * The coordinates themselves change and need to be copied to the GPU for every PME computation,
 158      * but reallocation happens only at DD.
 159      */
 160     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<gmx::RVec>) d_coordinates;
 161     /*! \brief Global GPU memory array handle with input atom charges.
 162      * The charges only need to be reallocated and copied to the GPU at DD step.
 163      */
 164     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_coefficients;
 165     /*! \brief Global GPU memory array handle with input/output rvec atom forces.
 166      * The forces change and need to be copied from (and possibly to) the GPU for every PME
 167      * computation, but reallocation happens only at DD.
 168      */
 169     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_forces;
 170     /*! \brief Global GPU memory array handle with ivec atom gridline indices.
 171      * Computed on GPU in the spline calculation part.
 172      */
 173     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<int>) d_gridlineIndices;
 174     /* B-spline parameters are computed entirely on GPU for every PME computation, not copied.
 175      * Unless we want to try something like GPU spread + CPU gather?
 176      */
 177     /*! \brief Global GPU memory array handle with B-spline values */
 178     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_theta;
 179     /*! \brief Global GPU memory array handle with B-spline derivative values */
 180     HIDE_FROM_OPENCL_COMPILER(DeviceBuffer<float>) d_dtheta;
 181 };
 182
 183 /*! \internal \brief
 184  * A GPU data structure for storing the PME data which might change for each new PME computation.
 185  */
 186 struct PmeGpuDynamicParams
 187 {
 188     /* The box parameters. The box only changes size with pressure coupling enabled. */
 189     /*! \brief
 190      * Reciprocal (inverted unit cell) box.
 191      *
 192      * The box is transposed as compared to the CPU pme->recipbox.
 193      * Basically, spread uses matrix columns (while solve and gather use rows).
 194      * This storage format might be not the most optimal since the box is always triangular so there are zeroes.
 195      */
 196     float recipBox[DIM][DIM];
 197     /*! \brief The unit cell volume for solving. */
 198     float boxVolume;
 199 };
 200
 201 /*! \internal \brief
 202  * A single structure encompassing all the PME data used in GPU kernels on device.
 203  * To extend the list with platform-specific parameters, this can be inherited by the
 204  * GPU framework-specific structure.
 205  */
 206 struct PmeGpuKernelParamsBase
 207 {
 208     /*! \brief Constant data that is set once. */
 209     struct PmeGpuConstParams constants;
 210     /*! \brief Data dependent on the grid size/cutoff. */
 211     struct PmeGpuGridParams grid;
 212     /*! \brief Data dependent on the DD and local atoms. */
 213     struct PmeGpuAtomParams atoms;
 214     /*! \brief Data that possibly changes for every new PME computation.
 215      * This should be kept up-to-date by calling pme_gpu_prepare_computation(...)
 216      * before launching spreading.
 217      */
 218     struct PmeGpuDynamicParams current;
 219     /* These texture objects are only used in CUDA and are related to the grid size. */
 220     /*! \brief Texture object for accessing grid.d_fractShiftsTable */
 221     HIDE_FROM_OPENCL_COMPILER(DeviceTexture) fractShiftsTableTexture;
 222     /*! \brief Texture object for accessing grid.d_gridlineIndicesTable */
 223     HIDE_FROM_OPENCL_COMPILER(DeviceTexture) gridlineIndicesTableTexture;
 224 };
 225
 226 #endif