Date: 2026-07-30T21:14:11+00:00

Actual source code: pbjacobi_cuda.cu

      1: #include <petscdevice_cuda.h>
      2: #include <petsc/private/petsclegacycupmblas.h>
      3: #include <../src/ksp/pc/impls/pbjacobi/pbjacobi.h>

      5: #if PETSC_PKG_CUDA_VERSION_LT(11, 7, 0)
      6: __global__ static void MatMultBatched(PetscInt bs, PetscInt mbs, const PetscScalar *A, const PetscScalar *x, PetscScalar *y, PetscBool transpose)
      7: {
      8:   const PetscInt gridSize = gridDim.x * blockDim.x;
      9:   PetscInt       row      = blockIdx.x * blockDim.x + threadIdx.x;
     10:   const PetscInt bs2      = bs * bs;

     12:   /* One row per thread. The blocks are stored in column-major order */
     13:   for (; row < bs * mbs; row += gridSize) {
     14:     const PetscScalar *Ap, *xp;
     15:     PetscScalar       *yp;
     16:     PetscInt           i, j, k;

     18:     k  = row / bs;                               /* k-th block */
     19:     i  = row % bs;                               /* this thread deals with i-th row of the block */
     20:     Ap = &A[bs2 * k + i * (transpose ? bs : 1)]; /* Ap points to the first entry of i-th row */
     21:     xp = &x[bs * k];
     22:     yp = &y[bs * k];
     23:     /* multiply i-th row (column) with x */
     24:     yp[i] = 0.0;
     25:     for (j = 0; j < bs; j++) {
     26:       yp[i] += Ap[0] * xp[j];
     27:       Ap += (transpose ? 1 : bs); /* block is in column major order */
     28:     }
     29:   }
     30: }
     31: #endif

     33: static PetscErrorCode PCApplyOrTranspose_PBJacobi_CUDA(PC pc, Vec x, Vec y, cublasOperation_t op)
     34: {
     35:   const PetscScalar *xx;
     36:   PetscScalar       *yy;
     37:   cublasHandle_t     handle;
     38:   PC_PBJacobi       *jac = (PC_PBJacobi *)pc->data;
     39:   const PetscScalar *A   = (const PetscScalar *)jac->spptr;
     40:   const PetscInt     bs = jac->bs, mbs = jac->mbs;

     42:   PetscFunctionBegin;
     43:   PetscCall(VecCUDAGetArrayRead(x, &xx));
     44:   PetscCall(VecCUDAGetArrayWrite(y, &yy));
     45:   PetscCall(PetscCUBLASGetHandle(&handle));
     46:   PetscCallCUBLAS(cublasSetPointerMode(handle, CUBLAS_POINTER_MODE_HOST)); /* alpha, beta are on host */

     48: #if PETSC_PKG_CUDA_VERSION_GE(11, 7, 0)
     49:   /* y = alpha op(A) x + beta y */
     50:   const PetscScalar alpha = 1.0, beta = 0.0;
     51:   PetscCallCUBLAS(cublasXgemvStridedBatched(handle, op, bs, bs, &alpha, A, bs, bs * bs, xx, 1, bs, &beta, yy, 1, bs, mbs));
     52: #else
     53:   PetscInt gridSize = PetscMin((bs * mbs + 255) / 256, 2147483647); /* <= 2^31-1 */
     54:   MatMultBatched<<<gridSize, 256>>>(bs, mbs, A, xx, yy, op == CUBLAS_OP_T ? PETSC_TRUE : PETSC_FALSE);
     55:   PetscCallCUDA(cudaGetLastError());
     56: #endif
     57:   PetscCall(VecCUDARestoreArrayRead(x, &xx));
     58:   PetscCall(VecCUDARestoreArrayWrite(y, &yy));
     59:   PetscCall(PetscLogGpuFlops(bs * bs * mbs * 2));
     60:   PetscFunctionReturn(PETSC_SUCCESS);
     61: }

     63: static PetscErrorCode PCApply_PBJacobi_CUDA(PC pc, Vec x, Vec y)
     64: {
     65:   PetscFunctionBegin;
     66:   PetscCall(PCApplyOrTranspose_PBJacobi_CUDA(pc, x, y, CUBLAS_OP_N)); // No transpose
     67:   PetscFunctionReturn(PETSC_SUCCESS);
     68: }

     70: static PetscErrorCode PCApplyTranspose_PBJacobi_CUDA(PC pc, Vec x, Vec y)
     71: {
     72:   PetscFunctionBegin;
     73:   PetscCall(PCApplyOrTranspose_PBJacobi_CUDA(pc, x, y, CUBLAS_OP_T)); // Transpose
     74:   PetscFunctionReturn(PETSC_SUCCESS);
     75: }

     77: static PetscErrorCode PCDestroy_PBJacobi_CUDA(PC pc)
     78: {
     79:   PC_PBJacobi *jac = (PC_PBJacobi *)pc->data;

     81:   PetscFunctionBegin;
     82:   PetscCallCUDA(cudaFree(jac->spptr));
     83:   PetscCall(PCDestroy_PBJacobi(pc));
     84:   PetscFunctionReturn(PETSC_SUCCESS);
     85: }

     87: PETSC_INTERN PetscErrorCode PCSetUp_PBJacobi_CUDA(PC pc, Mat diagVB)
     88: {
     89:   PC_PBJacobi *jac = (PC_PBJacobi *)pc->data;
     90:   size_t       size;

     92:   PetscFunctionBegin;
     93:   PetscCall(PCSetUp_PBJacobi_Host(pc, diagVB)); /* Compute the inverse on host now. Might worth doing it on device directly */
     94:   size = sizeof(PetscScalar) * jac->bs * jac->bs * jac->mbs;

     96:   /* PBJacobi_CUDA is simple so that we use jac->spptr as if it is diag_d */
     97:   if (!jac->spptr) PetscCallCUDAVoid(cudaMalloc(&jac->spptr, size));
     98:   PetscCallCUDAVoid(cudaMemcpy(jac->spptr, jac->diag, size, cudaMemcpyHostToDevice));
     99:   PetscCall(PetscLogCpuToGpu(size));

    101:   pc->ops->apply          = PCApply_PBJacobi_CUDA;
    102:   pc->ops->applytranspose = PCApplyTranspose_PBJacobi_CUDA;
    103:   pc->ops->destroy        = PCDestroy_PBJacobi_CUDA;
    104:   PetscFunctionReturn(PETSC_SUCCESS);
    105: }