optimization of max_pool3d grad (#45934)

paddle/phi/kernels/funcs/pooling.cu

@@ -2319,7 +2319,8 @@ __global__ void KernelMaxPool3DWithIdx(const int ncd,
 }
 
 template <typename T1, typename T2>
-__global__ void KernelMaxPool3DWithIdxGrad(const int nthreads,
+__global__ void KernelMaxPool3DWithIdxGrad(
+    const int ncd,
     const T1* output_grad,
     const T2* mask,
     const int channels,
@@ -2339,67 +2340,31 @@ __global__ void KernelMaxPool3DWithIdxGrad(const int nthreads,
     const int padding_height,
     const int padding_width,
     bool adaptive,
-                                           T1* input_grad) {
-  for (int index = blockIdx.x * blockDim.x + threadIdx.x; index < nthreads;
-       index += blockDim.x * gridDim.x) {
-    int w_offset = index % input_width;
-    int h_offset = (index / input_width) % input_height;
-    int d_offset = (index / input_width / input_height) % input_depth;
-    int c_offset =
-        (index / input_width / input_height / input_depth) % channels;
-    int batch_idx = index / input_width / input_height / input_depth / channels;
-
-    int pdstart, pdend;
-    int phstart, phend;
-    int pwstart, pwend;
-    if (adaptive) {
-      pdstart = d_offset * output_depth / input_depth;
-      pdend =
-          min((d_offset + 1) * output_depth / input_depth + 1, output_depth);
-      phstart = h_offset * output_height / input_height;
-      phend =
-          min((h_offset + 1) * output_height / input_height + 1, output_height);
-      pwstart = w_offset * output_width / input_width;
-      pwend =
-          min((w_offset + 1) * output_width / input_width + 1, output_width);
-    } else {
-      pdstart =
-          (d_offset + padding_depth < ksize_depth)
-              ? 0
-              : (d_offset + padding_depth - ksize_depth) / stride_depth + 1;
-      phstart =
-          (h_offset + padding_height < ksize_height)
-              ? 0
-              : (h_offset + padding_height - ksize_height) / stride_height + 1;
-      pwstart =
-          (w_offset + padding_width < ksize_width)
-              ? 0
-              : (w_offset + padding_width - ksize_width) / stride_width + 1;
-      pdend = min((d_offset + padding_depth) / stride_depth + 1, output_depth);
-      phend =
-          min((h_offset + padding_height) / stride_height + 1, output_height);
-      pwend = min((w_offset + padding_width) / stride_width + 1, output_width);
-    }
+    T1* input_grad,
+    FastDivModForPooling3D divmods_output) {
+  int w_offset, h_offset, d_offset, nc_offset;
 
-    T1 input_grad_data = 0;
-    int input_current_feature_map_idx =
-        (d_offset * input_height + h_offset) * input_width + w_offset;
-    int output_idx = (batch_idx * channels + c_offset) * output_depth *
-                     output_height * output_width;
-    mask += output_idx;
-    output_grad += output_idx;
+  w_offset = blockIdx.x * blockDim.x + threadIdx.x;
+  h_offset = blockIdx.y * blockDim.y + threadIdx.y;
 
-    for (int pd = pdstart; pd < pdend; ++pd) {
-      for (int ph = phstart; ph < phend; ++ph) {
-        for (int pw = pwstart; pw < pwend; ++pw) {
-          if (mask[(pd * output_height + ph) * output_width + pw] ==
-              input_current_feature_map_idx)
-            input_grad_data +=
-                output_grad[(pd * output_height + ph) * output_width + pw];
-        }
+  if (w_offset < output_width && h_offset < output_height) {
+    for (int index_z = blockIdx.z * blockDim.z + threadIdx.z; index_z < ncd;
+         index_z += gridDim.z * blockDim.z) {
+      auto output_depth_divmod = divmods_output.depth.Divmod(index_z);
+      d_offset = output_depth_divmod.val[1];
+      nc_offset = output_depth_divmod.val[0];
+      int output_index =
+          nc_offset * output_depth * output_height * output_width +
+          d_offset * output_height * output_width + h_offset * output_width +
+          w_offset;
+      int max_index = mask[output_index];
+      if (max_index != -1) {
+        paddle::platform::CudaAtomicAdd(
+            &input_grad[nc_offset * input_depth * input_height * input_width +
+                        max_index],
+            output_grad[output_index]);
       }
     }
-    input_grad[index] = input_grad_data;
   }
 }
 
@@ -2523,14 +2488,25 @@ class MaxPool3dWithIndexGradFunctor<phi::GPUContext, T1, T2> {
     const T2* mask_data = mask.data<T2>();
     T1* input_grad_data = context.template Alloc<T1>(input_grad);
 
-    int nthreads =
-        batch_size * input_channels * input_depth * input_height * input_width;
-    int blocks = (nthreads + 1024 - 1) / 1024;
-    dim3 threads(1024, 1);
-    dim3 grid(blocks, 1);
+    int ncd = batch_size * input_channels * output_depth;
+
+    int thread_x = 32;
+    int thread_y = 8;
+    int thread_z = 1;
+    dim3 threads(thread_x, thread_y, thread_z);
+    std::array<int, 3> max_grid_dim = context.GetCUDAMaxGridDimSize();
+    int block_x = (output_width + threads.x - 1) / threads.x;
+    int block_y = (output_height + threads.y - 1) / threads.y;
+    int block_z = (ncd > max_grid_dim[2] * threads.z)
+                      ? max_grid_dim[2]
+                      : (ncd + threads.z - 1) / threads.z;
+    dim3 grid(block_x, block_y, block_z);
+
+    auto pool_divmods_output = FastDivModForPooling3D(
+        input_channels, output_width, output_height, output_depth);
 
     KernelMaxPool3DWithIdxGrad<T1, T2>
-        <<<grid, threads, 0, context.stream()>>>(nthreads,
+        <<<grid, threads, 0, context.stream()>>>(ncd,
                                                  output_grad_data,
                                                  mask_data,
                                                  input_channels,
@@ -2550,7 +2526,8 @@ class MaxPool3dWithIndexGradFunctor<phi::GPUContext, T1, T2> {
                                                  padding_height,
                                                  padding_width,
                                                  adaptive,
-                                                 input_grad_data);
+                                                 input_grad_data,
+                                                 pool_divmods_output);
   }
 };