cumsum_kernel.cu

// Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// 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 "paddle/phi/kernels/cumsum_kernel.h"

#include <thrust/device_ptr.h>
#include <thrust/device_vector.h>
#include <thrust/reverse.h>
#include <thrust/scan.h>
#ifdef __NVCC__
#include <cub/cub.cuh>
#endif
#ifdef __HIPCC__
#include <hipcub/hipcub.hpp>
namespace cub = hipcub;
#endif

#include "paddle/phi/backends/gpu/gpu_context.h"
#include "paddle/phi/core/hostdevice.h"
#include "paddle/phi/core/kernel_registry.h"

namespace phi {

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];
  }
}

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;
    }

    BlockReverse<T, 1024>(
        matrix_data, reverse_data, src_offset, dst_offset, valid_item);
  }
}

template <typename T>
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;
  }
};

// No bank-conflict transpose
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;
    }
  }

  __syncthreads();

  x = blockIdx.y * TILE_DIM + threadIdx.x;  // transpose block offset
  y = blockIdx.x * TILE_DIM + threadIdx.y;

  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];
    }
  }
}

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;
    }

    int offset = bx * scan_size + block_offset + by * (inner_size * scan_size);

    T thread_keys[ITEMS_PER_THREAD];
    BlockLoadT(temp_storage.load)
        .Load(d_in + offset, thread_keys, valid_item, 0);

    __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);
  }
}

template <typename T, typename Context>
void CumsumKernel(const Context& dev_ctx,
                  const DenseTensor& x,
                  int axis,
                  bool flatten,
                  bool exclusive,
                  bool reverse,
                  DenseTensor* out) {
  auto out_dims = out->dims();
  auto size = x.numel();

  PADDLE_ENFORCE_EQ(
      axis < out_dims.size() && axis >= (0 - out_dims.size()),
      true,
      phi::errors::OutOfRange(
          "Attr(axis) is out of range, It's expected "
          "to be in range of [-%d, %d]. But received Attr(axis) = %d.",
          out_dims.size(),
          out_dims.size() - 1,
          axis));
  if (axis < 0) {
    axis += out_dims.size();
  }

  T* out_data = dev_ctx.template Alloc<T>(out);
  const T* in_data = x.data<T>();

  // Use thrust for parallel acceleration when the input size is equal to the
  // length of the ‘axis’ dimension.
  if (size == out_dims[axis]) {
#ifdef __HIPCC__
    const auto& policy = thrust::hip::par.on(dev_ctx.stream());
#else
    const auto& policy = thrust::cuda::par.on(dev_ctx.stream());
#endif
    if (reverse) {
      thrust::reverse_iterator<thrust::device_ptr<const T>> reversed_in(
          thrust::device_pointer_cast(in_data) + size);
      thrust::reverse_iterator<thrust::device_ptr<T>> reversed_out(
          thrust::device_pointer_cast(out_data) + size);
      if (exclusive) {
        thrust::exclusive_scan(
            policy, reversed_in, reversed_in + size, reversed_out);
      } else {
        thrust::inclusive_scan(
            policy, reversed_in, reversed_in + size, reversed_out);
      }
    } else {
      if (exclusive) {
        thrust::exclusive_scan(policy, in_data, in_data + size, out_data);
      } else {
        thrust::inclusive_scan(policy, in_data, in_data + size, out_data);
      }
    }
    return;
  }

  size_t height = 1;
  size_t width = 1;
  for (size_t i = 0; i <= axis; i++) {
    height *= out_dims[i];
  }

  for (size_t i = axis + 1; i < out_dims.size(); 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);
  out->Resize(out_dims);
  auto* tmp_data = out->data<T>();

  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 {
      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 {
    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);
  }
}

}  // namespace phi

PD_REGISTER_KERNEL(cumsum,
                   GPU,
                   ALL_LAYOUT,
                   phi::CumsumKernel,
                   float,
                   double,
                   int16_t,
                   int,
                   int64_t) {}