From b818429ae7ecadde20136c7340bc6dc1497ebc0b Mon Sep 17 00:00:00 2001
From: wangchaochaohu <wangchao66@baidu.com>
Date: Sat, 28 Nov 2020 22:58:19 +0800
Subject: [PATCH] optimize cumsum OP (#29193)

---
 paddle/fluid/operators/cumsum_op.cu | 449 ++++++++++++----------------
 1 file changed, 196 insertions(+), 253 deletions(-)

diff --git a/paddle/fluid/operators/cumsum_op.cu b/paddle/fluid/operators/cumsum_op.cu
index 85cbf444a5..4bf839f748 100644
--- a/paddle/fluid/operators/cumsum_op.cu
+++ b/paddle/fluid/operators/cumsum_op.cu
@@ -14,8 +14,10 @@ limitations under the License. */
 
 #include <thrust/device_ptr.h>
 #include <thrust/device_vector.h>
+#include <thrust/gather.h>
 #include <thrust/reverse.h>
 #include <thrust/scan.h>
+#include "cub/cub.cuh"
 #include "paddle/fluid/operators/cum_op.h"
 #include "paddle/fluid/platform/gpu_launch_config.h"
 
@@ -25,223 +27,157 @@ using LoDTensor = paddle::framework::LoDTensor;
 namespace paddle {
 namespace operators {
 
-template <typename T>
-__global__ void OuterScan(const T* in, T* out, int inner_dim_size,
-                          int outer_dim_size, int scan_dim_size, bool exclusive,
-                          bool reverse) {
-  int id = blockIdx.y * blockDim.x + threadIdx.x;
-
-  for (int outer_index = blockIdx.x; outer_index < outer_dim_size;
-       outer_index += gridDim.x) {
-    for (int inner_index = blockIdx.y * blockDim.x + threadIdx.x;
-         inner_index < inner_dim_size; inner_index += gridDim.y * blockDim.x) {
-      int scan_index_init = 0;
-      int forward_direction = 1;
-      int src_index =
-          outer_index * scan_dim_size * inner_dim_size + inner_index;
-      int dst_index =
-          outer_index * scan_dim_size * inner_dim_size + inner_index;
-      if (reverse) {
-        src_index = src_index + (scan_dim_size - 1) * inner_dim_size;
-        dst_index = dst_index + (scan_dim_size - 1) * inner_dim_size;
-        forward_direction = -1;
-      }
-      if (exclusive) {
-        scan_index_init = 1;
-        out[dst_index] = 0;
-        dst_index = dst_index + (forward_direction * inner_dim_size);
-      }
-      T acc = 0;
-
-      for (int scan_index = scan_index_init; scan_index < scan_dim_size;
-           ++scan_index) {
-        acc = in[src_index] + acc;
-        out[dst_index] = acc;
-        src_index += (forward_direction * inner_dim_size);
-        dst_index += (forward_direction * inner_dim_size);
-      }
-    }
+template <typename T, int BLOCK_SIZE>
+__device__ void BlockReverse(const T* idata, T* odata, int src_base,
+                             int dst_base, int valid_item) {
+  __shared__ T sh_mem[BLOCK_SIZE];
+  int tx = threadIdx.x;
+
+  int offset = tx;
+  int in_index = src_base + offset;
+  if (offset >= valid_item) {
+    sh_mem[offset] = 0;
+  } else {
+    int sh_mem_index = BLOCK_SIZE - offset - 1;
+    T data = idata[in_index];
+    sh_mem[sh_mem_index] = data;
+  }
+
+  __syncthreads();
+  int out_index = dst_base - offset;
+  if (offset < valid_item) {
+    int sh_mem_index = BLOCK_SIZE - offset - 1;
+    odata[out_index] = sh_mem[sh_mem_index];
   }
 }
 
-// inclusive scan
-template <typename T, int num_threads_x, int num_threads_y>
-__global__ void InnerMostDimInclusiveScan(const T* in, T* out,
-                                          int inner_dim_size,
-                                          int outer_dim_size, int scan_dim_size,
-                                          bool reverse) {
-  __shared__ T share_data[num_threads_y][num_threads_x * 2];
-  T* share_row = share_data[threadIdx.y];
-  int forward_direction = 1;
-  if (reverse) forward_direction = -1;
-
-  for (int block_row = blockIdx.x * blockDim.y; block_row < outer_dim_size;
-       block_row += blockDim.y * gridDim.x) {
-    int row = block_row + threadIdx.y;
-    T acc = 0;
-    const T* row_src = in + row * scan_dim_size;
-    T* row_dst = out + row * scan_dim_size;
-    int block_col = 0;
-    bool loop_condition = (block_col < scan_dim_size);
-    if (reverse) {
-      loop_condition = (block_col >= 0);
-      block_col = scan_dim_size - 1;
+template <typename T>
+__global__ void MatrixRowReverse(const T* matrix_data, T* reverse_data,
+                                 int reverse_size, int outer_size,
+                                 int inner_size) {
+  int bx = blockIdx.x;
+  int by = blockIdx.y;
+  int item_per_block = 1024;
+
+  for (int block_offset = 0; block_offset < reverse_size;
+       block_offset += item_per_block) {
+    int valid_item = (reverse_size - block_offset > item_per_block)
+                         ? item_per_block
+                         : reverse_size - block_offset;
+    int src_offset =
+        bx * reverse_size + block_offset + by * (inner_size * reverse_size);
+    int dst_offset = bx * reverse_size + by * (inner_size * reverse_size) +
+                     reverse_size - 1 - block_offset;
+    if (reverse_size < item_per_block) {
+      valid_item = reverse_size;
     }
-    while (loop_condition) {
-      // Load data into share memory(two value per thread)
-      int col1 = block_col + threadIdx.x * forward_direction;
-      int col2 = block_col + (num_threads_x + threadIdx.x) * forward_direction;
-      if (row < outer_dim_size) {
-        if (col1 < scan_dim_size && col1 >= 0) {
-          share_row[threadIdx.x] = row_src[col1];
-        } else {
-          share_row[threadIdx.x] = 0;
-        }
 
-        if (col2 < scan_dim_size && col2 >= 0) {
-          share_row[num_threads_x + threadIdx.x] = row_src[col2];
-        } else {
-          share_row[num_threads_x + threadIdx.x] = 0;
-        }
-
-        // Add the previous block acc to the result
-        if (threadIdx.x == 0) {
-          share_row[0] = share_row[0] + acc;
-        }
-      }
-      __syncthreads();
-
-      // Up-Sweep
-      for (unsigned s = num_threads_x, d = 1; s >= 1; s >>= 1, d <<= 1) {
-        if (row < outer_dim_size && threadIdx.x < s) {
-          unsigned offset = (2 * threadIdx.x + 1) * d - 1;
-          share_row[offset + d] = share_row[offset] + share_row[offset + d];
-        }
-        __syncthreads();
-      }
-      // Down-Sweep
-      for (unsigned s = 2, d = blockDim.x / 2; d >= 1; s <<= 1, d >>= 1) {
-        if (row < outer_dim_size && threadIdx.x < s - 1) {
-          unsigned offset = 2 * (threadIdx.x + 1) * d - 1;
-          share_row[offset + d] = share_row[offset] + share_row[offset + d];
-        }
-        __syncthreads();
-      }
-
-      // Write to the output
-      if (row < outer_dim_size) {
-        if (col1 < scan_dim_size && col1 >= 0)
-          row_dst[col1] = share_row[threadIdx.x];
-        if (col2 < scan_dim_size && col2 >= 0)
-          row_dst[col2] = share_row[num_threads_x + threadIdx.x];
-      }
-      acc = share_row[2 * num_threads_x - 1];
-      __syncthreads();
-      block_col += 2 * num_threads_x * forward_direction;
-      if (reverse)
-        loop_condition = (block_col >= 0);
-      else
-        loop_condition = (block_col < scan_dim_size);
-    }
+    BlockReverse<T, 1024>(matrix_data, reverse_data, src_offset, dst_offset,
+                          valid_item);
   }
 }
 
-// exclusive block scan and store block sum for large scan
 template <typename T>
-__global__ void InnerMostDimExclusiveScan(const T* in, T* out, T* sum_data,
-                                          int inner_dim_size,
-                                          int outer_dim_size, int scan_dim_size,
-                                          int two_power, bool reverse) {
-  // https://stackoverflow.com/questions/27570552/templated-cuda-kernel-with-dynamic-shared-memory
-  extern __shared__ __align__(sizeof(T)) unsigned char raw_tmp[];
-  T* share_tmp = reinterpret_cast<T*>(raw_tmp);
-  int thread_id = threadIdx.x;
-  int block_id = blockIdx.x;
-  int block_scan_size = blockDim.x * 2;
-  int remain = scan_dim_size % (2 * blockDim.x);
-  if (block_id == gridDim.x - 1 && remain != 0) block_scan_size = remain;
-  int col1 = thread_id;
-  int col2 = thread_id + (block_scan_size) / 2;
-  int index1 = blockIdx.y * (scan_dim_size) + block_id * blockDim.x * 2 + col1;
-  int index2 = blockIdx.y * (scan_dim_size) + block_id * blockDim.x * 2 + col2;
-  if (reverse) {
-    index1 = blockIdx.y * (scan_dim_size) + scan_dim_size - 1 -
-             (block_id * blockDim.x * 2 + col1);
-    index2 = blockIdx.y * (scan_dim_size) + scan_dim_size - 1 -
-             (block_id * blockDim.x * 2 + col2);
-  }
-  int sum_index = blockIdx.y * gridDim.x + block_id;
-  if (thread_id < block_scan_size) {
-    share_tmp[col1 + (col1 >> 5)] = in[index1];
-    share_tmp[col2 + (col2 >> 5)] = in[index2];
-  } else {
-    share_tmp[col1 + (col1 >> 5)] = 0;
-    share_tmp[col2 + (col2 >> 5)] = 0;
+struct BlockPrefixCallbackOp {
+  // Running prefix
+  T running_total;
+  // Constructor
+  __device__ BlockPrefixCallbackOp(T running_total)
+      : running_total(running_total) {}
+  // Callback operator to be entered by the first warp of threads in the block.
+  // Thread-0 is responsible for returning a value for seeding the block-wide
+  // scan.
+  __device__ T operator()(T block_aggregate) {
+    T old_prefix = running_total;
+    running_total = old_prefix + block_aggregate;
+    return old_prefix;
   }
+};
 
-  // Up-Sweep
-  int offset = 1;
-  for (int d = (two_power / 2); d > 0; d >>= 1) {
-    __syncthreads();
-    if (thread_id < d) {
-      int tmp_index1 = offset * (2 * thread_id + 1) - 1;
-      int tmp_index2 = offset * (2 * thread_id + 2) - 1;
-      tmp_index1 = tmp_index1 + (tmp_index1 >> 5);
-      tmp_index2 = tmp_index2 + (tmp_index2 >> 5);
-
-      share_tmp[tmp_index2] += share_tmp[tmp_index1];
+// No bank-conflict transpose
+// Same as transposeCoalesced except the first tile dimension is padded
+// to avoid shared memory bank conflicts.
+template <typename T, int TILE_DIM, int BLOCK_ROWS>
+__global__ void MatrixTranspose(T* odata, const T* idata, size_t height,
+                                size_t width) {
+  __shared__ T tile[TILE_DIM][TILE_DIM + 1];
+
+  int x = blockIdx.x * TILE_DIM + threadIdx.x;
+  int y = blockIdx.y * TILE_DIM + threadIdx.y;
+  for (int j = 0; j < TILE_DIM; j += BLOCK_ROWS) {
+    if (x < width && (y + j) < height) {
+      tile[threadIdx.y + j][threadIdx.x] = idata[(y + j) * width + x];
+    } else {
+      tile[threadIdx.y + j][threadIdx.x] = 0;
     }
-    offset *= 2;
   }
+
   __syncthreads();
 
-  if (thread_id == 0) {
-    int tmp_index = (two_power - 1) + ((two_power - 1) >> 5);
-    sum_data[sum_index] = share_tmp[tmp_index];
-    share_tmp[tmp_index] = 0;
-  }
+  x = blockIdx.y * TILE_DIM + threadIdx.x;  // transpose block offset
+  y = blockIdx.x * TILE_DIM + threadIdx.y;
 
-  // Down Sweep
-  for (int d = 1; d < two_power; d *= 2) {
-    offset >>= 1;
-    __syncthreads();
-    if (thread_id < d) {
-      int tmp_index1 = offset * (2 * thread_id + 1) - 1;
-      int tmp_index2 = offset * (2 * thread_id + 2) - 1;
-      tmp_index1 = tmp_index1 + (tmp_index1 >> 5);
-      tmp_index2 = tmp_index2 + (tmp_index2 >> 5);
-
-      T tmp = share_tmp[tmp_index1];
-      share_tmp[tmp_index1] = share_tmp[tmp_index2];
-      share_tmp[tmp_index2] += tmp;
+  for (int j = 0; j < TILE_DIM; j += BLOCK_ROWS) {
+    if (x < height && (y + j) < width) {
+      odata[(y + j) * height + x] = tile[threadIdx.x][threadIdx.y + j];
     }
   }
+}
 
-  __syncthreads();
+template <typename T, int BLOCK_THREADS, int ITEMS_PER_THREAD>
+__global__ void BlockScanKernel(T* d_out, const T* d_in, int inner_size,
+                                int outer_size, int scan_size, bool exclusive) {
+  // Specialize BlockLoad, BlockStore, and BlockRadixSort collective types
+  typedef cub::BlockLoad<T, BLOCK_THREADS, ITEMS_PER_THREAD,
+                         cub::BLOCK_LOAD_TRANSPOSE>
+      BlockLoadT;
+  typedef cub::BlockStore<T, BLOCK_THREADS, ITEMS_PER_THREAD,
+                          cub::BLOCK_STORE_TRANSPOSE>
+      BlockStoreT;
+  typedef cub::BlockScan<T, BLOCK_THREADS> BlockScanT;
+  // Allocate type-safe, repurposable shared memory for collectives
+  __shared__ union {
+    typename BlockLoadT::TempStorage load;
+    typename BlockStoreT::TempStorage store;
+    typename BlockScanT::TempStorage scan;
+  } temp_storage;
+
+  int bx = blockIdx.x;
+  int by = blockIdx.y;
+
+  BlockPrefixCallbackOp<T> prefix_op(0);
+  T block_aggregate = static_cast<T>(0);
+
+  // Obtain this block's segment of consecutive keys (blocked across threads)
+  int item_per_block = BLOCK_THREADS * ITEMS_PER_THREAD;
+  for (int block_offset = 0; block_offset < scan_size;
+       block_offset += BLOCK_THREADS * ITEMS_PER_THREAD) {
+    int valid_item = (scan_size - block_offset > item_per_block)
+                         ? item_per_block
+                         : (scan_size - block_offset);
+    if (scan_size < item_per_block) {
+      valid_item = scan_size;
+    }
 
-  if (col1 < block_scan_size) out[index1] = share_tmp[col1 + (col1 >> 5)];
-  if (col2 < block_scan_size) out[index2] = share_tmp[col2 + (col2 >> 5)];
-}
+    int offset = bx * scan_size + block_offset + by * (inner_size * scan_size);
 
-// for large scan_dim_size array we need to add for correct result
-template <typename T>
-__global__ void AddBlockScan(T* result, T* sum, int size, int scan_dim_size,
-                             int sum_size, bool reverse) {
-  int idx = threadIdx.x + blockDim.x * (blockIdx.x + blockIdx.y * gridDim.x);
-  int block_id_start = blockIdx.y * sum_size;
-  int block_id_end = blockIdx.x + blockIdx.y * sum_size;
-  int block_id = blockIdx.x;
-  int thread_id = threadIdx.x;
-
-  int col = block_id * blockDim.x + thread_id + size;
-  int index = blockIdx.y * (scan_dim_size) + col;
-  if (reverse) {
-    index = blockIdx.y * (scan_dim_size) + scan_dim_size - 1 - col;
-  }
+    T thread_keys[ITEMS_PER_THREAD];
+    BlockLoadT(temp_storage.load)
+        .Load(d_in + offset, thread_keys, valid_item, 0);
 
-  if (col >= scan_dim_size || col < 0) return;
-  for (int i = block_id_start; i <= block_id_end; i++) {
-    result[index] += sum[i];
+    __syncthreads();
+    if (exclusive) {
+      T init_value = static_cast<T>(0);
+      BlockScanT(temp_storage.scan)
+          .ExclusiveScan(thread_keys, thread_keys, cub::Sum(), prefix_op);
+    } else {
+      BlockScanT(temp_storage.scan)
+          .InclusiveScan(thread_keys, thread_keys, cub::Sum(), prefix_op);
+    }
+    __syncthreads();
+
+    BlockStoreT(temp_storage.store)
+        .Store(d_out + offset, thread_keys, valid_item);
   }
 }
 
@@ -298,72 +234,79 @@ class CumCUDAKernel : public framework::OpKernel<T> {
       return;
     }
 
-    const int& scan_dim_size = out_dims[axis];
-    bool optimize_condition = (axis == (out_dims.size() - 1)) ? true : false;
-    int outer_dim_size = 1;
-    int inner_dim_size = 1;
-    // treat all dim index < axis as outer_dim_size
-    for (size_t i = 0; i < axis; i++) {
-      outer_dim_size *= out_dims[i];
+    size_t height = 1;
+    size_t width = 1;
+    for (size_t i = 0; i <= axis; i++) {
+      height *= out_dims[i];
     }
-    // treat all dim index > axis as innner_dim_size
+
     for (size_t i = axis + 1; i < out_dims.size(); i++) {
-      inner_dim_size *= out_dims[i];
+      width *= out_dims[i];
     }
+    int scan_size = out_dims[axis];
+    bool transpose = (axis != out_dims.size() - 1);
 
+    int tile_size = 32;
+    dim3 blocks(32, 8);
+    dim3 transpose_grids((width + tile_size - 1) / tile_size,
+                         (height + tile_size - 1) / tile_size);
     auto& dev_ctx = context.template device_context<DeviceContext>();
-    if (optimize_condition) {
-      auto nextPowerOfTwo = [](int x) -> int {
-        int ret = 1;
-        while (ret < x) ret = ret * 2;
-        return ret;
-      };
-      if (exclusive) {
-        int element_per_block = nextPowerOfTwo(scan_dim_size) / 2;
-        if (element_per_block > 512 || element_per_block < 32) {
-          element_per_block = 64;
-        }
-        int two_power = element_per_block * 2;
-        dim3 block(element_per_block);
-        dim3 grid(((scan_dim_size + 1) / 2 + block.x - 1) / block.x,
-                  outer_dim_size);
-        int offset_size = (element_per_block * 2) >> 5;
-        int share_mem_size = (element_per_block * 2 + offset_size) * sizeof(T);
-        Tensor scan_sum;
-        paddle::framework::DDim dims{
-            ((scan_dim_size + 1) / 2 + block.x - 1) / block.x, outer_dim_size};
-        scan_sum.Resize(dims);
-        T* sum_data = scan_sum.mutable_data<T>(context.GetPlace());
-        InnerMostDimExclusiveScan<
-            T><<<grid, block, share_mem_size, dev_ctx.stream()>>>(
-            in_data, out_data, sum_data, inner_dim_size, outer_dim_size,
-            scan_dim_size, two_power, reverse);
-        // for large scan array we need to do add for correct result
-        int element_size = element_per_block * 2;
-        if (scan_dim_size > element_size) {
-          dim3 sum_block(element_per_block * 2);
-          dim3 sum_grid((scan_dim_size - element_size + block.x - 1) / block.x,
-                        outer_dim_size);
-          int sum_size = ((scan_dim_size + 1) / 2 + block.x - 1) / block.x;
-          AddBlockScan<T><<<sum_grid, sum_block, 0, dev_ctx.stream()>>>(
-              out_data, sum_data, element_size, scan_dim_size, sum_size,
-              reverse);
-        }
-
+    Tensor tmp;
+    tmp.Resize(out_dims);
+    auto* tmp_data = tmp.mutable_data<T>(context.GetPlace());
+    T* next_in_data = out_data;
+    T* next_out_data = tmp_data;
+    if (transpose) {
+      MatrixTranspose<T, 32,
+                      8><<<transpose_grids, blocks, 0, dev_ctx.stream()>>>(
+          out_data, in_data, height, width);
+      next_in_data = out_data;
+      next_out_data = tmp_data;
+    }
+    auto swap_ptr = [](T*& ptr1, T*& ptr2) {
+      T* tmp = ptr2;
+      ptr2 = ptr1;
+      ptr1 = tmp;
+    };
+    int outer_size = height / scan_size;
+    int inner_size = width;
+    // Consider the size of shared memory, here block size is 128
+    dim3 scan_grid(outer_size, inner_size);
+    dim3 reverse_grid = scan_grid;
+    if (reverse) {
+      if (transpose) {
+        reverse_grid.x = scan_grid.y;
+        reverse_grid.y = scan_grid.x;
+        MatrixRowReverse<T><<<reverse_grid, 1024, 0, dev_ctx.stream()>>>(
+            next_in_data, next_out_data, scan_size, outer_size, inner_size);
+        if (!transpose) next_in_data = tmp_data;
+        swap_ptr(next_in_data, next_out_data);
       } else {
-        dim3 block(32, 16);
-        dim3 grid((outer_dim_size + block.y - 1) / block.y);
-        InnerMostDimInclusiveScan<T, 32,
-                                  16><<<grid, block, 0, dev_ctx.stream()>>>(
-            in_data, out_data, inner_dim_size, outer_dim_size, scan_dim_size,
-            reverse);
+        MatrixRowReverse<T><<<reverse_grid, 1024, 0, dev_ctx.stream()>>>(
+            in_data, out_data, scan_size, outer_size, inner_size);
       }
+    }
+    if (!transpose && !reverse) {
+      BlockScanKernel<T, 128, 4><<<scan_grid, 128, 0, dev_ctx.stream()>>>(
+          out_data, in_data, outer_size, inner_size, scan_size, exclusive);
+
     } else {
-      dim3 block(std::min(512, inner_dim_size));
-      dim3 grid(outer_dim_size, (inner_dim_size + block.x - 1) / block.x);
-      OuterScan<T><<<grid, block, 0, dev_ctx.stream()>>>(
-          in_data, out_data, inner_dim_size, outer_dim_size, scan_dim_size,
-          exclusive, reverse);
+      BlockScanKernel<T, 128, 4><<<scan_grid, 128, 0, dev_ctx.stream()>>>(
+          next_out_data, next_in_data, outer_size, inner_size, scan_size,
+          exclusive);
+    }
+    swap_ptr(next_in_data, next_out_data);
+    if (reverse) {
+      MatrixRowReverse<T><<<reverse_grid, 1024, 0, dev_ctx.stream()>>>(
+          next_in_data, next_out_data, scan_size, outer_size, inner_size);
+      swap_ptr(next_in_data, next_out_data);
+    }
+    if (transpose) {
+      transpose_grids.x = (height + tile_size - 1) / tile_size;
+      transpose_grids.y = (width + tile_size - 1) / tile_size;
+      MatrixTranspose<T, 32,
+                      8><<<transpose_grids, blocks, 0, dev_ctx.stream()>>>(
+          next_out_data, next_in_data, width, height);
     }
   }
 };
-- 
GitLab