Fix GPU X buffer ops with empty domain

The early return that ensured no kernel gets launched with empty domain
got dropped with recent refactoring. This change adds back the
conditional and fixes assertion errors triggered with empty domains.

Change-Id: I508fdc2179877080dec512695e96310b52698b81

diff --git a/src/gromacs/nbnxm/cuda/nbnxm_cuda.cu b/src/gromacs/nbnxm/cuda/nbnxm_cuda.cu
index a273193b0237f71c6465f68441343c3f3a3283b9..0d250f464756e733123882007064ea84a5eefc5d 100644 (file)
--- a/src/gromacs/nbnxm/cuda/nbnxm_cuda.cu
+++ b/src/gromacs/nbnxm/cuda/nbnxm_cuda.cu
@@ -761,9 +761,8 @@ void nbnxn_gpu_copy_x_to_gpu(const Nbnxm::Grid               &grid,
 
     cudaStream_t               stream  = nb->stream[interactionLoc];
 
-    // FIXME: need to either let the local stream get to the
-    // insertNonlocalGpuDependency call or call it separately here
-    if (nCopyAtoms == 0) // empty domain
+    // empty domain avoid launching zero-byte copy
+    if (nCopyAtoms == 0)
     {
         if (interactionLoc == Nbnxm::InteractionLocality::Local)
         {
@@ -816,35 +815,38 @@ void nbnxn_gpu_x_to_nbat_x(const Nbnxm::Grid               &grid,
     // TODO: This will only work with CUDA
     GMX_ASSERT(coordinatesDevice,  "Need a valid device pointer");
 
-    /* launch kernel on GPU */
-
-    KernelLaunchConfig config;
-    config.blockSize[0]     = c_bufOpsThreadsPerBlock;
-    config.blockSize[1]     = 1;
-    config.blockSize[2]     = 1;
-    config.gridSize[0]      = (grid.numCellsColumnMax()*numAtomsPerCell + c_bufOpsThreadsPerBlock - 1)/c_bufOpsThreadsPerBlock;
-    config.gridSize[1]      = numColumns;
-    config.gridSize[2]      = 1;
-    GMX_ASSERT(config.gridSize[0] > 0, "Can not have empty grid, early return above avoids this");
-    config.sharedMemorySize = 0;
-    config.stream           = stream;
-
-    auto       kernelFn            = nbnxn_gpu_x_to_nbat_x_kernel;
-    float     *xqPtr               = &(adat->xq->x);
-    const int *d_atomIndices       = nb->atomIndices;
-    const int *d_cxy_na            = &nb->cxy_na[numColumnsMax*gridId];
-    const int *d_cxy_ind           = &nb->cxy_ind[numColumnsMax*gridId];
-    const auto kernelArgs          = prepareGpuKernelArguments(kernelFn, config,
-                                                               &numColumns,
-                                                               &xqPtr,
-                                                               &setFillerCoords,
-                                                               &coordinatesDevice,
-                                                               &d_atomIndices,
-                                                               &d_cxy_na,
-                                                               &d_cxy_ind,
-                                                               &cellOffset,
-                                                               &numAtomsPerCell);
-    launchGpuKernel(kernelFn, config, nullptr, "XbufferOps", kernelArgs);
+    int numAtoms = grid.srcAtomEnd() - grid.srcAtomBegin();
+    // avoid empty kernel launch, skip to inserting stream dependency
+    if (numAtoms != 0)
+    {
+        KernelLaunchConfig config;
+        config.blockSize[0]     = c_bufOpsThreadsPerBlock;
+        config.blockSize[1]     = 1;
+        config.blockSize[2]     = 1;
+        config.gridSize[0]      = (grid.numCellsColumnMax()*numAtomsPerCell + c_bufOpsThreadsPerBlock - 1)/c_bufOpsThreadsPerBlock;
+        config.gridSize[1]      = numColumns;
+        config.gridSize[2]      = 1;
+        GMX_ASSERT(config.gridSize[0] > 0, "Can not have empty grid, early return above avoids this");
+        config.sharedMemorySize = 0;
+        config.stream           = stream;
+
+        auto       kernelFn       = nbnxn_gpu_x_to_nbat_x_kernel;
+        float     *xqPtr          = &(adat->xq->x);
+        const int *d_atomIndices  = nb->atomIndices;
+        const int *d_cxy_na       = &nb->cxy_na[numColumnsMax*gridId];
+        const int *d_cxy_ind      = &nb->cxy_ind[numColumnsMax*gridId];
+        const auto kernelArgs     = prepareGpuKernelArguments(kernelFn, config,
+                                                              &numColumns,
+                                                              &xqPtr,
+                                                              &setFillerCoords,
+                                                              &coordinatesDevice,
+                                                              &d_atomIndices,
+                                                              &d_cxy_na,
+                                                              &d_cxy_ind,
+                                                              &cellOffset,
+                                                              &numAtomsPerCell);
+        launchGpuKernel(kernelFn, config, nullptr, "XbufferOps", kernelArgs);
+    }
 
     nbnxnInsertNonlocalGpuDependency(nb, interactionLoc);
 }