From befd6d53383b160cac492a92f9358fd59f0861c7 Mon Sep 17 00:00:00 2001
From: Zhang Ting <zhangting_2017@163.com>
Date: Thu, 3 Dec 2020 17:34:21 +0800
Subject: [PATCH] improve elementwise_add_grad perf (#29277)

* improve performance of elementwise_sum_grad
---
 .../elementwise/elementwise_add_op.cu         | 309 +++++++++++++++++-
 .../elementwise/elementwise_add_op.h          |  60 ++--
 2 files changed, 332 insertions(+), 37 deletions(-)

diff --git a/paddle/fluid/operators/elementwise/elementwise_add_op.cu b/paddle/fluid/operators/elementwise/elementwise_add_op.cu
index 8de6416065d..e460a96cbfc 100644
--- a/paddle/fluid/operators/elementwise/elementwise_add_op.cu
+++ b/paddle/fluid/operators/elementwise/elementwise_add_op.cu
@@ -11,12 +11,16 @@ distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License. */
+#include <algorithm>
+#include <functional>
 #include "paddle/fluid/operators/elementwise/elementwise_add_op.h"
 #include "paddle/fluid/operators/elementwise/elementwise_op_function.cu.h"
 #include "paddle/fluid/platform/complex128.h"
 #include "paddle/fluid/platform/complex64.h"
 #include "paddle/fluid/platform/float16.h"
 
+#define WARPSIZE 32
+
 namespace ops = paddle::operators;
 namespace plat = paddle::platform;
 
@@ -74,11 +78,10 @@ static __global__ void SimpleElemwiseAddGradCUDAKernel(const T* dout,
 template <typename DeviceContext, typename T>
 typename std::enable_if<
     std::is_same<DeviceContext, plat::CUDADeviceContext>::value>::type
-elementwise_add_grad(const framework::ExecutionContext& ctx,
-                     const framework::Tensor* x, const framework::Tensor* y,
-                     const framework::Tensor* out,
-                     const framework::Tensor* dout, framework::Tensor* dx,
-                     framework::Tensor* dy) {
+ElementwiseAddGrad(const framework::ExecutionContext& ctx,
+                   const framework::Tensor* x, const framework::Tensor* y,
+                   const framework::Tensor* out, const framework::Tensor* dout,
+                   framework::Tensor* dx, framework::Tensor* dy) {
   dim3 block_size = dim3(PADDLE_CUDA_THREAD_SIZE, 1);
   auto size = x->numel();
   dim3 grid_size =
@@ -90,6 +93,302 @@ elementwise_add_grad(const framework::ExecutionContext& ctx,
       dy->mutable_data<T>(ctx.GetPlace()));
 }
 
+inline static bool UseReduceFirstAxisRank1(const framework::DDim& dout_dims,
+                                           const framework::DDim& x_dims,
+                                           const framework::DDim& y_dims,
+                                           const int axis) {
+  int start_axis =
+      (axis == -1 ? std::abs(x_dims.size() - y_dims.size()) : axis);
+
+  if (y_dims[y_dims.size() - 1] == 1) {
+    return false;
+  }
+
+  if (y_dims.size() > 1) {
+    for (int i = 0; i < y_dims.size() - 1; ++i) {
+      if (y_dims[i] != 1) {
+        return false;
+      }
+    }
+    return true;
+  } else if (start_axis == x_dims.size() - 1) {
+    return true;
+  }
+  return false;
+}
+
+inline static bool UseReduceFirstAxisRank2(const framework::DDim& dout_dims,
+                                           const framework::DDim& x_dims,
+                                           const framework::DDim& y_dims,
+                                           const int axis) {
+  int start_axis =
+      (axis == -1 ? std::abs(x_dims.size() - y_dims.size()) : axis);
+
+  if (y_dims.size() < 2 ||
+      x_dims[x_dims.size() - 2] != y_dims[y_dims.size() - 2] ||
+      x_dims[x_dims.size() - 1] != y_dims[y_dims.size() - 1]) {
+    return false;
+  }
+
+  if (start_axis == x_dims.size() - 2) {
+    return true;
+  } else if (start_axis == 0) {
+    for (int i = 0; i < y_dims.size() - 2; ++i) {
+      if (y_dims[i] != 1) {
+        return false;
+      }
+    }
+    return true;
+  }
+  return false;
+}
+
+inline static bool UseReduceSecondAxisRank2(const framework::DDim& dout_dims,
+                                            const framework::DDim& x_dims,
+                                            const framework::DDim& y_dims,
+                                            const int axis, int* start,
+                                            int* end) {
+  if (x_dims.size() != y_dims.size() || y_dims.size() < 3) {
+    return false;
+  }
+
+  auto y_dims_vec = framework::vectorize(y_dims);
+  auto start_iter = std::find(y_dims_vec.begin(), y_dims_vec.end(), 1);
+  auto end_iter = std::find(y_dims_vec.rbegin(), y_dims_vec.rend(), 1);
+  if (start_iter == y_dims_vec.end() || start_iter == y_dims_vec.end() - 1) {
+    return false;
+  } else {
+    *start = std::distance(y_dims_vec.begin(), start_iter);
+    *end = y_dims_vec.size() - 1 - std::distance(y_dims_vec.rbegin(), end_iter);
+    for (int i = *start; i <= *end; ++i) {
+      if (y_dims[i] != 1) {
+        return false;
+      }
+    }
+    return true;
+  }
+}
+
+template <typename T, typename OP>
+__global__ __launch_bounds__(1024) void ReduceFirstAixsKernel(
+    const T* in, T* out, const int64_t num_rows, const int64_t num_cols, OP op,
+    T init) {
+  int row = blockIdx.y * blockDim.y + threadIdx.y;
+  int col = blockIdx.x * blockDim.x + threadIdx.x;
+
+  T sum = init;
+  if (row < num_rows && col < num_cols) sum = in[row * num_cols + col];
+
+  __shared__ __align__(
+      alignof(T)) char partial_sums_raw[WARPSIZE * (WARPSIZE + 1) * sizeof(T)];
+  T* partial_sums = reinterpret_cast<T*>(partial_sums_raw);
+
+  row += gridDim.y * blockDim.y;
+
+  if (col < num_cols) {
+    for (; row < num_rows; row += gridDim.y * blockDim.y) {
+      sum = op(sum, in[row * num_cols + col]);
+    }
+  }
+
+  partial_sums[threadIdx.x * (WARPSIZE + 1) + threadIdx.y] = sum;
+
+  __syncthreads();
+
+  if (threadIdx.y == 0 && col < num_cols) {
+    T s = partial_sums[threadIdx.x * (WARPSIZE + 1)];
+
+    const int numRowsThisBlock = min(static_cast<int64_t>(blockDim.y),
+                                     num_rows - blockIdx.y * blockDim.y);
+
+    for (int row = 1; row < numRowsThisBlock; ++row) {
+      T t = partial_sums[threadIdx.x * (WARPSIZE + 1) + row];
+      s = op(s, t);
+    }
+
+    out[col * gridDim.y + blockIdx.y] = s;
+  }
+}
+
+template <typename DeviceContext, typename T>
+static void ElemwiseYGradRank1CUDA(const framework::ExecutionContext& ctx,
+                                   const framework::Tensor& dout,
+                                   const int rows, const int cols,
+                                   framework::Tensor* dx,
+                                   framework::Tensor* dy) {
+  dim3 block_dim(WARPSIZE, std::min(rows, 1024 / WARPSIZE));
+  dim3 grid_dim((cols + (WARPSIZE - 1)) / WARPSIZE, 1, 1);
+
+  if (dx) {
+    dx->mutable_data<T>(ctx.GetPlace());
+    framework::TensorCopy(
+        dout, ctx.GetPlace(),
+        ctx.template device_context<platform::DeviceContext>(), dx);
+  }
+  if (dy) {
+    dy->mutable_data<T>(ctx.GetPlace());
+    const T* dout_data = dout.data<T>();
+    T* dy_data = dy->data<T>();
+    auto stream = ctx.template device_context<DeviceContext>().stream();
+    ReduceFirstAixsKernel<<<grid_dim, block_dim, 0, stream>>>(
+        dout_data, dy_data, rows, cols, AddFunctor<T>(), static_cast<T>(0));
+  }
+}
+
+template <typename T, typename OP>
+__global__ __launch_bounds__(1024) void ReduceFirstOrSecondAxisKernel(
+    const T* in, T* out, const int num_planes, const int num_rows,
+    const int num_cols, OP op, T init) {
+  const int gid = threadIdx.x + blockIdx.x * blockDim.x;
+  const int elems_per_plane = num_rows * num_cols;
+
+  const int plane = gid / num_cols;
+  const int col = gid % num_cols;
+
+  if (plane >= num_planes) return;
+
+  if (num_rows == 1) {
+    out[plane * elems_per_plane + col] = in[plane * elems_per_plane + col];
+    return;
+  }
+
+  T sum = op(in[plane * elems_per_plane + col],
+             in[plane * elems_per_plane + num_cols + col]);
+  for (int row = 2; row < num_rows; ++row) {
+    sum = op(sum, in[plane * elems_per_plane + row * num_cols + col]);
+  }
+
+  out[plane * num_cols + col] = sum;
+}
+
+template <typename DeviceContext, typename T>
+static void ElemwiseYGradRank2CUDA(const framework::ExecutionContext& ctx,
+                                   const framework::Tensor& dout,
+                                   const int planes, const int rows,
+                                   const int cols, framework::Tensor* dx,
+                                   framework::Tensor* dy) {
+  int num_threads = 128;
+  int num_blocks = (rows + num_threads - 1) / num_threads;
+
+  if (planes != 1) {
+    num_blocks = (planes * cols + num_threads - 1) / num_threads;
+  }
+
+  if (dx) {
+    dx->mutable_data<T>(ctx.GetPlace());
+    framework::TensorCopy(
+        dout, ctx.GetPlace(),
+        ctx.template device_context<platform::DeviceContext>(), dx);
+  }
+  if (dy) {
+    dy->mutable_data<T>(ctx.GetPlace());
+    const T* dout_data = dout.data<T>();
+    T* dy_data = dy->data<T>();
+    auto stream = ctx.template device_context<DeviceContext>().stream();
+    ReduceFirstOrSecondAxisKernel<<<num_blocks, num_threads, 0, stream>>>(
+        dout_data, dy_data, planes, rows, cols, AddFunctor<T>(),
+        static_cast<T>(0));
+  }
+}
+
+template <typename DeviceContext, typename T>
+static bool ElemwiseGradUseReduce(const framework::ExecutionContext& ctx,
+                                  const int axis, const framework::DDim x_dims,
+                                  const framework::DDim y_dims,
+                                  const framework::Tensor& dout,
+                                  framework::Tensor* dx,
+                                  framework::Tensor* dy) {
+  int start = 0;
+  int end = 0;
+  auto x_dims_vec = framework::vectorize(x_dims);
+  if (UseReduceFirstAxisRank1(dout.dims(), x_dims, y_dims, axis)) {
+    int rows = std::accumulate(x_dims_vec.begin(), x_dims_vec.end() - 1, 1,
+                               std::multiplies<int>());
+    int cols = dx->dims()[dx->dims().size() - 1];
+    if (cols > 512 && cols < 4096) {
+      ElemwiseYGradRank1CUDA<DeviceContext, T>(ctx, dout, rows, cols, dx, dy);
+      return true;
+    }
+  }
+
+  if (UseReduceFirstAxisRank2(dout.dims(), x_dims, y_dims, axis)) {
+    int rows = std::accumulate(x_dims_vec.begin(), x_dims_vec.end() - 2, 1,
+                               std::multiplies<int>());
+    int cols =
+        dx->dims()[dx->dims().size() - 1] * dx->dims()[dx->dims().size() - 2];
+    if (cols > 4096) {
+      ElemwiseYGradRank2CUDA<DeviceContext, T>(ctx, dout, 1, rows, cols, dx,
+                                               dy);
+      return true;
+    }
+  }
+
+  if (UseReduceSecondAxisRank2(dout.dims(), x_dims, y_dims, axis, &start,
+                               &end)) {
+    int planes = std::accumulate(x_dims_vec.begin(), x_dims_vec.begin() + start,
+                                 1, std::multiplies<int>());
+    int rows = std::accumulate(x_dims_vec.begin() + start,
+                               x_dims_vec.begin() + end + 1, 1,
+                               std::multiplies<int>());
+    int cols = std::accumulate(x_dims_vec.begin() + end + 1, x_dims_vec.end(),
+                               1, std::multiplies<int>());
+    if (rows / (planes * cols) < 16) {
+      ElemwiseYGradRank2CUDA<DeviceContext, T>(ctx, dout, planes, rows, cols,
+                                               dx, dy);
+      return true;
+    }
+  }
+
+  return false;
+}
+
+template <typename T>
+class ElementwiseAddGradKernel<platform::CUDADeviceContext, T>
+    : public ElemwiseGradKernel<T> {
+ public:
+  void Compute(const framework::ExecutionContext& ctx) const override {
+    ElemwiseGradKernel<T>::Compute(ctx);
+
+    using Tensor = framework::Tensor;
+
+    auto* x = ctx.Input<Tensor>("X");
+    auto* y = ctx.Input<Tensor>("Y");
+    auto* dout = ctx.Input<Tensor>(framework::GradVarName("Out"));
+    auto* dx = ctx.Output<Tensor>(framework::GradVarName("X"));
+    auto* dy = ctx.Output<Tensor>(framework::GradVarName("Y"));
+    // skip out
+    auto* out = dout;
+    int axis = ctx.Attr<int>("axis");
+
+    // Special case when dy is not needed and dx doesn't reduce
+    if (dx != nullptr && dy == nullptr && dx->dims() == dout->dims()) {
+      VLOG(4) << "Special case when dy is not needed and dx doesn't "
+                 "reduce";
+      framework::TensorCopy(
+          *dout, ctx.GetPlace(),
+          ctx.template device_context<platform::DeviceContext>(), dx);
+    } else if (dx == nullptr && dy != nullptr && dy->dims() == dout->dims()) {
+      VLOG(4) << "Special case when dx is not needed and dy doesn't "
+                 "reduce";
+      framework::TensorCopy(
+          *dout, ctx.GetPlace(),
+          ctx.template device_context<platform::DeviceContext>(), dy);
+    } else if (dx && dy && (dx->dims() == dy->dims())) {
+      ElementwiseAddGrad<platform::CUDADeviceContext, T>(ctx, x, y, out, dout,
+                                                         dx, dy);
+    } else if (dx && dx->dims() == dout->dims() &&
+               ElemwiseGradUseReduce<platform::CUDADeviceContext, T>(
+                   ctx, axis, x->dims(), y->dims(), *dout, dx, dy)) {
+    } else if (dy && dy->dims() == dout->dims() &&
+               ElemwiseGradUseReduce<platform::CUDADeviceContext, T>(
+                   ctx, axis, x->dims(), y->dims(), *dout, dy, dx)) {
+    } else {
+      DefaultElementwiseAddGrad<platform::CUDADeviceContext, T>(ctx, x, y, out,
+                                                                dout, dx, dy);
+    }
+  }
+};
+
 }  // namespace operators
 }  // namespace paddle
 REGISTER_OP_CUDA_KERNEL(
diff --git a/paddle/fluid/operators/elementwise/elementwise_add_op.h b/paddle/fluid/operators/elementwise/elementwise_add_op.h
index acda31e0f23..23223fc06d3 100644
--- a/paddle/fluid/operators/elementwise/elementwise_add_op.h
+++ b/paddle/fluid/operators/elementwise/elementwise_add_op.h
@@ -22,9 +22,10 @@ namespace paddle {
 namespace operators {
 
 template <typename DeviceContext, typename T>
-void default_elementwise_add(const framework::ExecutionContext &ctx,
-                             const framework::Tensor *x,
-                             const framework::Tensor *y, framework::Tensor *z) {
+void DefaultElementwiseAddGrad(const framework::ExecutionContext &ctx,
+                               const framework::Tensor *x,
+                               const framework::Tensor *y,
+                               framework::Tensor *z) {
   int axis = ctx.Attr<int>("axis");
   auto x_dims = x->dims();
   auto y_dims = y->dims();
@@ -57,7 +58,7 @@ class ElementwiseAddKernel : public framework::OpKernel<T> {
       SameDimsElemwiseAdd<DeviceContext, T> same_dims_add;
       same_dims_add(ctx, x, y, z);
     } else {
-      default_elementwise_add<DeviceContext, T>(ctx, x, y, z);
+      DefaultElementwiseAddGrad<DeviceContext, T>(ctx, x, y, z);
     }
   }
 };
@@ -68,13 +69,12 @@ struct IdentityGrad {
 };
 
 template <typename DeviceContext, typename T>
-void default_elementwise_add_grad(const framework::ExecutionContext &ctx,
-                                  const framework::Tensor *x,
-                                  const framework::Tensor *y,
-                                  const framework::Tensor *out,
-                                  const framework::Tensor *dout,
-                                  framework::Tensor *dx,
-                                  framework::Tensor *dy) {
+void DefaultElementwiseAddGrad(const framework::ExecutionContext &ctx,
+                               const framework::Tensor *x,
+                               const framework::Tensor *y,
+                               const framework::Tensor *out,
+                               const framework::Tensor *dout,
+                               framework::Tensor *dx, framework::Tensor *dy) {
   int axis = ctx.Attr<int>("axis");
 
   ElemwiseExplicitGradCompute<DeviceContext, T, IdentityGrad<T>,
@@ -87,11 +87,10 @@ template <typename DeviceContext, typename T>
 typename std::enable_if<
     std::is_floating_point<T>::value &&
     std::is_same<DeviceContext, platform::CPUDeviceContext>::value>::type
-elementwise_add_grad(const framework::ExecutionContext &ctx,
-                     const framework::Tensor *x, const framework::Tensor *y,
-                     const framework::Tensor *out,
-                     const framework::Tensor *dout, framework::Tensor *dx,
-                     framework::Tensor *dy) {
+ElementwiseAddGrad(const framework::ExecutionContext &ctx,
+                   const framework::Tensor *x, const framework::Tensor *y,
+                   const framework::Tensor *out, const framework::Tensor *dout,
+                   framework::Tensor *dx, framework::Tensor *dy) {
   auto blas = math::GetBlas<DeviceContext, T>(ctx);
   if (dx) {
     blas.VCOPY(dout->numel(), dout->data<T>(),
@@ -108,12 +107,11 @@ template <typename DeviceContext, typename T>
 typename std::enable_if<
     !std::is_floating_point<T>::value &&
     std::is_same<DeviceContext, platform::CPUDeviceContext>::value>::type
-elementwise_add_grad(const framework::ExecutionContext &ctx,
-                     const framework::Tensor *x, const framework::Tensor *y,
-                     const framework::Tensor *out,
-                     const framework::Tensor *dout, framework::Tensor *dx,
-                     framework::Tensor *dy) {
-  default_elementwise_add_grad<DeviceContext, T>(ctx, x, y, out, dout, dx, dy);
+ElementwiseAddGrad(const framework::ExecutionContext &ctx,
+                   const framework::Tensor *x, const framework::Tensor *y,
+                   const framework::Tensor *out, const framework::Tensor *dout,
+                   framework::Tensor *dx, framework::Tensor *dy) {
+  DefaultElementwiseAddGrad<DeviceContext, T>(ctx, x, y, out, dout, dx, dy);
 }
 
 #ifdef PADDLE_WITH_CUDA
@@ -121,11 +119,10 @@ elementwise_add_grad(const framework::ExecutionContext &ctx,
 template <typename DeviceContext, typename T>
 typename std::enable_if<
     std::is_same<DeviceContext, platform::CUDADeviceContext>::value>::type
-elementwise_add_grad(const framework::ExecutionContext &ctx,
-                     const framework::Tensor *x, const framework::Tensor *y,
-                     const framework::Tensor *out,
-                     const framework::Tensor *dout, framework::Tensor *dx,
-                     framework::Tensor *dy);
+ElementwiseAddGrad(const framework::ExecutionContext &ctx,
+                   const framework::Tensor *x, const framework::Tensor *y,
+                   const framework::Tensor *out, const framework::Tensor *dout,
+                   framework::Tensor *dx, framework::Tensor *dy);
 #endif
 
 template <typename DeviceContext, typename T>
@@ -158,10 +155,9 @@ class ElementwiseAddGradKernel : public ElemwiseGradKernel<T> {
           *dout, ctx.GetPlace(),
           ctx.template device_context<platform::DeviceContext>(), dy);
     } else if (dx != nullptr && dy != nullptr && (dx->dims() == dy->dims())) {
-      elementwise_add_grad<DeviceContext, T>(ctx, x, y, out, dout, dx, dy);
+      ElementwiseAddGrad<DeviceContext, T>(ctx, x, y, out, dout, dx, dy);
     } else {
-      default_elementwise_add_grad<DeviceContext, T>(ctx, x, y, out, dout, dx,
-                                                     dy);
+      DefaultElementwiseAddGrad<DeviceContext, T>(ctx, x, y, out, dout, dx, dy);
     }
   }
 };
@@ -186,8 +182,8 @@ class ElementwiseAddDoubleGradKernel : public framework::OpKernel<T> {
       GetDoubleGradSafeTensor<DeviceContext, T>(ctx, y, ddy, &ddy_safe);
 
       ddout->mutable_data<T>(ctx.GetPlace());
-      default_elementwise_add<DeviceContext, T>(ctx, &ddx_safe, &ddy_safe,
-                                                ddout);
+      DefaultElementwiseAddGrad<DeviceContext, T>(ctx, &ddx_safe, &ddy_safe,
+                                                  ddout);
     }
   }
 };
-- 
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