apex/csrc/megatron/generic_scaled_masked_softmax.cpp

/* coding=utf-8
 * Copyright (c) 2022, NVIDIA CORPORATION.  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 <cuda_fp16.h>
#include <torch/extension.h>
#include <vector>

namespace multihead_attn
{
  namespace fused_softmax
  {
    namespace generic_scaled_masked_softmax
    {

      torch::Tensor fwd_cuda(
          torch::Tensor const &input,
          torch::Tensor const &mask,
          float scale_factor);

      torch::Tensor bwd_cuda(
          torch::Tensor const &output_grads,
          torch::Tensor const &softmax_results,
          float scale_factor);

      torch::Tensor fwd(
          torch::Tensor const &input,
          torch::Tensor const &mask,
          float scale_factor)
      {
        TORCH_CHECK(input.dim() == 4, "expected 4D tensor");
        TORCH_CHECK((input.scalar_type() == at::ScalarType::Half) ||
                       (input.scalar_type() == at::ScalarType::BFloat16),
                   "Only fp16 and bf16 are supported");
        TORCH_CHECK(mask.dim() == 4, "expected 4D tensor");

        return fwd_cuda(input, mask, scale_factor);
      }

      torch::Tensor bwd(
          torch::Tensor const &output_grads,
          torch::Tensor const &softmax_results,
          float scale_factor)
      {

        TORCH_CHECK(output_grads.dim() == 4, "expected 3D tensor");
        TORCH_CHECK(softmax_results.dim() == 4, "expected 3D tensor");

        TORCH_CHECK((output_grads.scalar_type() == at::ScalarType::Half) ||
                       (output_grads.scalar_type() == at::ScalarType::BFloat16),
                   "Only fp16 and bf16 are supported");
        TORCH_CHECK((softmax_results.scalar_type() == at::ScalarType::Half) ||
                       (softmax_results.scalar_type() == at::ScalarType::BFloat16),
                   "Only fp16 and bf16 are supported");

        return bwd_cuda(output_grads, softmax_results, scale_factor);
      }

    } // end namespace generic_scaled_masked_softmax
  }   // end namespace fused_softmax
} // end namespace multihead_attn

PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
  m.def("forward",
        &multihead_attn::fused_softmax::generic_scaled_masked_softmax::fwd,
	"Self Multihead Attention scaled, time masked softmax -- Forward.");

  m.def("backward",
        &multihead_attn::fused_softmax::generic_scaled_masked_softmax::bwd,
	"Self Multihead Attention scaled, time masked softmax -- Backward.");
}