src/gromacs/ewald/pme_gpu_utils.h

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  35 #ifndef GMX_EWALD_PME_GPU_UTILS_H
  36 #define GMX_EWALD_PME_GPU_UTILS_H
  37
  38 /*! \internal \file
  39  * \brief This file defines small PME GPU inline host/device functions.
  40  * Note that OpenCL device-side functions can't use C++ features, so they are
  41  * located in a similar file pme_gpu_utils.clh.
  42  * Be sure to keep the logic in sync in both files when changing it!
  43  *
  44  * \author Aleksei Iupinov <a.yupinov@gmail.com>
  45  * \ingroup module_ewald
  46  */
  47
  48 #include "config.h"
  49
  50 #include <cassert>
  51
  52 #include "pme_gpu_constants.h"
  53
  54 //! A macro for inline GPU functions.
  55 #if GMX_GPU == GMX_GPU_CUDA
  56 #    define INLINE_EVERYWHERE __host__ __device__ __forceinline__
  57 #else
  58 #    define INLINE_EVERYWHERE inline
  59 #endif
  60
  61 /*! \internal \brief
  62  * Gets a base of the unique index to an element in a spline parameter buffer (theta/dtheta),
  63  * which is laid out for GPU spread/gather kernels. The base only corresponds to the atom index within the execution block.
  64  * Feed the result into getSplineParamIndex() to get a full index.
  65  * TODO: it's likely that both parameters can be just replaced with a single atom index, as they are derived from it.
  66  * Do that, verifying that the generated code is not bloated, and/or revise the spline indexing scheme.
  67  * Removing warp dependency would also be nice (and would probably coincide with removing c_pmeSpreadGatherAtomsPerWarp).
  68  *
  69  * \tparam order               PME order
  70  * \tparam atomsPerWarp        Number of atoms processed by a warp
  71  * \param[in] warpIndex        Warp index wrt the block.
  72  * \param[in] atomWarpIndex    Atom index wrt the warp (from 0 to atomsPerWarp - 1).
  73  *
  74  * \returns Index into theta or dtheta array using GPU layout.
  75  */
  76 template<int order, int atomsPerWarp>
  77 int INLINE_EVERYWHERE getSplineParamIndexBase(int warpIndex, int atomWarpIndex)
  78 {
  79     assert((atomWarpIndex >= 0) && (atomWarpIndex < atomsPerWarp));
  80     const int dimIndex    = 0;
  81     const int splineIndex = 0;
  82     // The zeroes are here to preserve the full index formula for reference
  83     return (((splineIndex + order * warpIndex) * DIM + dimIndex) * atomsPerWarp + atomWarpIndex);
  84 }
  85
  86 /*! \internal \brief
  87  * Gets a unique index to an element in a spline parameter buffer (theta/dtheta),
  88  * which is laid out for GPU spread/gather kernels. The index is wrt to the execution block,
  89  * in range(0, atomsPerBlock * order * DIM).
  90  * This function consumes result of getSplineParamIndexBase() and adjusts it for \p dimIndex and \p splineIndex.
  91  *
  92  * \tparam order               PME order
  93  * \tparam atomsPerWarp        Number of atoms processed by a warp
  94  * \param[in] paramIndexBase   Must be result of getSplineParamIndexBase().
  95  * \param[in] dimIndex         Dimension index (from 0 to 2)
  96  * \param[in] splineIndex      Spline contribution index (from 0 to \p order - 1)
  97  *
  98  * \returns Index into theta or dtheta array using GPU layout.
  99  */
 100 template<int order, int atomsPerWarp>
 101 int INLINE_EVERYWHERE getSplineParamIndex(int paramIndexBase, int dimIndex, int splineIndex)
 102 {
 103     assert((dimIndex >= XX) && (dimIndex < DIM));
 104     assert((splineIndex >= 0) && (splineIndex < order));
 105     return (paramIndexBase + (splineIndex * DIM + dimIndex) * atomsPerWarp);
 106 }
 107
 108 #if GMX_GPU == GMX_GPU_CUDA
 109 // CUDA device code helpers below
 110
 111 /*! \internal \brief
 112  * An inline CUDA function for checking the global atom data indices against the atom data array sizes.
 113  *
 114  * \param[in] atomDataIndex        The atom data index.
 115  * \param[in] nAtomData            The atom data array element count.
 116  * \returns                        Non-0 if index is within bounds (or PME data padding is enabled), 0 otherwise.
 117  *
 118  * This is called from the spline_and_spread and gather PME kernels.
 119  * The goal is to isolate the global range checks, and allow avoiding them with c_usePadding enabled.
 120  */
 121 int __device__ __forceinline__ pme_gpu_check_atom_data_index(const int atomDataIndex, const int nAtomData)
 122 {
 123     return c_usePadding ? 1 : (atomDataIndex < nAtomData);
 124 }
 125
 126 /*! \internal \brief
 127  * An inline CUDA function for skipping the zero-charge atoms.
 128  *
 129  * \returns                        Non-0 if atom should be processed, 0 otherwise.
 130  * \param[in] coefficient          The atom charge.
 131  *
 132  * This is called from the spline_and_spread and gather PME kernels.
 133  */
 134 int __device__ __forceinline__ pme_gpu_check_atom_charge(const float coefficient)
 135 {
 136     assert(isfinite(coefficient));
 137     return c_skipNeutralAtoms ? (coefficient != 0.0f) : 1;
 138 }
 139
 140 #endif
 141
 142 #endif