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39 * \brief Implements PME GPU spline calculation and charge spreading in CUDA.
40 * TODO: consider always pre-sorting particles (as in DD case).
42 * \author Aleksei Iupinov <a.yupinov@gmail.com>
49 #include "gromacs/gpu_utils/cuda_kernel_utils.cuh"
50 #include "gromacs/gpu_utils/typecasts.cuh"
53 #include "pme_gpu_calculate_splines.cuh"
57 * Charge spreading onto the grid.
58 * This corresponds to the CPU function spread_coefficients_bsplines_thread().
59 * Optional second stage of the spline_and_spread_kernel.
61 * \tparam[in] order PME interpolation order.
62 * \tparam[in] wrapX Whether the grid overlap in dimension X should be wrapped.
63 * \tparam[in] wrapY Whether the grid overlap in dimension Y should be wrapped.
64 * \tparam[in] useOrderThreads Whether we should use order threads per atom (order*order used if false).
66 * \param[in] kernelParams Input PME CUDA data in constant memory.
67 * \param[in] atomCharge Atom charge/coefficient of atom processed by thread.
68 * \param[in] sm_gridlineIndices Atom gridline indices in the shared memory.
69 * \param[in] sm_theta Atom spline values in the shared memory.
71 template<const int order, const bool wrapX, const bool wrapY, const bool useOrderThreads>
72 __device__ __forceinline__ void spread_charges(const PmeGpuCudaKernelParams kernelParams,
73 const float* atomCharge,
74 const int* __restrict__ sm_gridlineIndices,
75 const float* __restrict__ sm_theta)
77 /* Global memory pointer to the output grid */
78 float* __restrict__ gm_grid = kernelParams.grid.d_realGrid;
81 const int atomsPerWarp = useOrderThreads ? c_pmeSpreadGatherAtomsPerWarp4ThPerAtom
82 : c_pmeSpreadGatherAtomsPerWarp;
84 const int nx = kernelParams.grid.realGridSize[XX];
85 const int ny = kernelParams.grid.realGridSize[YY];
86 const int nz = kernelParams.grid.realGridSize[ZZ];
87 const int pny = kernelParams.grid.realGridSizePadded[YY];
88 const int pnz = kernelParams.grid.realGridSizePadded[ZZ];
90 const int offx = 0, offy = 0, offz = 0; // unused for now
92 const int atomIndexLocal = threadIdx.z;
94 const int chargeCheck = pme_gpu_check_atom_charge(*atomCharge);
97 // Spline Z coordinates
98 const int ithz = threadIdx.x;
100 const int ixBase = sm_gridlineIndices[atomIndexLocal * DIM + XX] - offx;
101 const int iyBase = sm_gridlineIndices[atomIndexLocal * DIM + YY] - offy;
102 int iz = sm_gridlineIndices[atomIndexLocal * DIM + ZZ] - offz + ithz;
107 /* Atom index w.r.t. warp - alternating 0 1 0 1 .. */
108 const int atomWarpIndex = atomIndexLocal % atomsPerWarp;
109 /* Warp index w.r.t. block - could probably be obtained easier? */
110 const int warpIndex = atomIndexLocal / atomsPerWarp;
112 const int splineIndexBase = getSplineParamIndexBase<order, atomsPerWarp>(warpIndex, atomWarpIndex);
113 const int splineIndexZ = getSplineParamIndex<order, atomsPerWarp>(splineIndexBase, ZZ, ithz);
114 const float thetaZ = sm_theta[splineIndexZ];
116 /* loop not used if order*order threads per atom */
117 const int ithyMin = useOrderThreads ? 0 : threadIdx.y;
118 const int ithyMax = useOrderThreads ? order : threadIdx.y + 1;
119 for (int ithy = ithyMin; ithy < ithyMax; ithy++)
121 int iy = iyBase + ithy;
122 if (wrapY & (iy >= ny))
127 const int splineIndexY = getSplineParamIndex<order, atomsPerWarp>(splineIndexBase, YY, ithy);
128 float thetaY = sm_theta[splineIndexY];
129 const float Val = thetaZ * thetaY * (*atomCharge);
130 assert(isfinite(Val));
131 const int offset = iy * pnz + iz;
134 for (int ithx = 0; (ithx < order); ithx++)
136 int ix = ixBase + ithx;
137 if (wrapX & (ix >= nx))
141 const int gridIndexGlobal = ix * pny * pnz + offset;
142 const int splineIndexX =
143 getSplineParamIndex<order, atomsPerWarp>(splineIndexBase, XX, ithx);
144 const float thetaX = sm_theta[splineIndexX];
145 assert(isfinite(thetaX));
146 assert(isfinite(gm_grid[gridIndexGlobal]));
147 atomicAdd(gm_grid + gridIndexGlobal, thetaX * Val);
154 * A spline computation and charge spreading kernel function.
156 * Two tuning parameters can be used for additional performance. For small systems and for debugging
157 * writeGlobal should be used removing the need to recalculate the theta values in the gather kernel.
158 * Similarly for useOrderThreads large systems order threads per atom gives higher performance than order*order threads
160 * \tparam[in] order PME interpolation order.
161 * \tparam[in] computeSplines A boolean which tells if the spline parameter and
162 * gridline indices' computation should be performed.
163 * \tparam[in] spreadCharges A boolean which tells if the charge spreading should be performed.
164 * \tparam[in] wrapX A boolean which tells if the grid overlap in dimension X should be wrapped.
165 * \tparam[in] wrapY A boolean which tells if the grid overlap in dimension Y should be wrapped.
166 * \tparam[in] writeGlobal A boolean which tells if the theta values and gridlines should be written to global memory.
167 * \tparam[in] useOrderThreads A boolean which tells if we should use order threads per atom (order*order used if false).
168 * \param[in] kernelParams Input PME CUDA data in constant memory.
170 template<const int order, const bool computeSplines, const bool spreadCharges, const bool wrapX, const bool wrapY, const bool writeGlobal, const bool useOrderThreads>
171 __launch_bounds__(c_spreadMaxThreadsPerBlock) CLANG_DISABLE_OPTIMIZATION_ATTRIBUTE __global__
172 void pme_spline_and_spread_kernel(const PmeGpuCudaKernelParams kernelParams)
174 const int atomsPerBlock =
175 useOrderThreads ? c_spreadMaxThreadsPerBlock / c_pmeSpreadGatherThreadsPerAtom4ThPerAtom
176 : c_spreadMaxThreadsPerBlock / c_pmeSpreadGatherThreadsPerAtom;
177 // Gridline indices, ivec
178 __shared__ int sm_gridlineIndices[atomsPerBlock * DIM];
180 __shared__ float sm_theta[atomsPerBlock * DIM * order];
183 const int atomsPerWarp = useOrderThreads ? c_pmeSpreadGatherAtomsPerWarp4ThPerAtom
184 : c_pmeSpreadGatherAtomsPerWarp;
189 const int blockIndex = blockIdx.y * gridDim.x + blockIdx.x;
190 const int atomIndexOffset = blockIndex * atomsPerBlock;
192 /* Thread index w.r.t. block */
193 const int threadLocalId =
194 (threadIdx.z * (blockDim.x * blockDim.y)) + (threadIdx.y * blockDim.x) + threadIdx.x;
195 /* Warp index w.r.t. block - could probably be obtained easier? */
196 const int warpIndex = threadLocalId / warp_size;
198 /* Atom index w.r.t. warp */
199 const int atomWarpIndex = threadIdx.z % atomsPerWarp;
200 /* Atom index w.r.t. block/shared memory */
201 const int atomIndexLocal = warpIndex * atomsPerWarp + atomWarpIndex;
202 /* Atom index w.r.t. global memory */
203 const int atomIndexGlobal = atomIndexOffset + atomIndexLocal;
205 /* Early return for fully empty blocks at the end
206 * (should only happen for billions of input atoms)
208 if (atomIndexOffset >= kernelParams.atoms.nAtoms)
212 /* Charges, required for both spline and spread */
213 if (c_useAtomDataPrefetch)
215 __shared__ float sm_coefficients[atomsPerBlock];
216 pme_gpu_stage_atom_data<float, atomsPerBlock, 1>(sm_coefficients, kernelParams.atoms.d_coefficients);
218 atomCharge = sm_coefficients[atomIndexLocal];
222 atomCharge = kernelParams.atoms.d_coefficients[atomIndexGlobal];
227 const float3* __restrict__ gm_coordinates = asFloat3(kernelParams.atoms.d_coordinates);
228 if (c_useAtomDataPrefetch)
231 __shared__ float3 sm_coordinates[atomsPerBlock];
233 /* Staging coordinates */
234 pme_gpu_stage_atom_data<float3, atomsPerBlock, 1>(sm_coordinates, gm_coordinates);
236 atomX = sm_coordinates[atomIndexLocal];
240 atomX = gm_coordinates[atomIndexGlobal];
242 calculate_splines<order, atomsPerBlock, atomsPerWarp, false, writeGlobal>(
243 kernelParams, atomIndexOffset, atomX, atomCharge, sm_theta, &dtheta, sm_gridlineIndices);
248 /* Staging the data for spread
249 * (the data is assumed to be in GPU global memory with proper layout already,
250 * as in after running the spline kernel)
252 /* Spline data - only thetas (dthetas will only be needed in gather) */
253 pme_gpu_stage_atom_data<float, atomsPerBlock, DIM * order>(sm_theta, kernelParams.atoms.d_theta);
254 /* Gridline indices */
255 pme_gpu_stage_atom_data<int, atomsPerBlock, DIM>(sm_gridlineIndices,
256 kernelParams.atoms.d_gridlineIndices);
264 spread_charges<order, wrapX, wrapY, useOrderThreads>(kernelParams, &atomCharge,
265 sm_gridlineIndices, sm_theta);
269 //! Kernel instantiations
270 template __global__ void pme_spline_and_spread_kernel<4, true, true, true, true, true, true>(const PmeGpuCudaKernelParams);
271 template __global__ void
272 pme_spline_and_spread_kernel<4, true, false, true, true, true, true>(const PmeGpuCudaKernelParams);
273 template __global__ void
274 pme_spline_and_spread_kernel<4, false, true, true, true, true, true>(const PmeGpuCudaKernelParams);
276 template __global__ void
277 pme_spline_and_spread_kernel<4, true, true, true, true, false, true>(const PmeGpuCudaKernelParams);
279 template __global__ void
280 pme_spline_and_spread_kernel<4, true, true, true, true, true, false>(const PmeGpuCudaKernelParams);
281 template __global__ void
282 pme_spline_and_spread_kernel<4, true, false, true, true, true, false>(const PmeGpuCudaKernelParams);
283 template __global__ void
284 pme_spline_and_spread_kernel<4, false, true, true, true, true, false>(const PmeGpuCudaKernelParams);
286 template __global__ void
287 pme_spline_and_spread_kernel<4, true, true, true, true, false, false>(const PmeGpuCudaKernelParams);