multilinguality_megatron/megatron/fused_kernels/scaled_softmax.cpp

/* Copyright (c) 2022, NVIDIA CORPORATION. All rights reserved. */

#include <cuda_fp16.h>
#include <torch/extension.h>
#include <vector>

namespace multihead_attn {
namespace fused_softmax {
namespace scaled_softmax {

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

  return fwd_cuda(input, scale_factor);
}

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

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

  AT_ASSERTM((output_grads.scalar_type() == at::ScalarType::Half) ||
	     (output_grads.scalar_type() == at::ScalarType::BFloat16), 
      "Only fp16 and bf16 are supported");
  AT_ASSERTM((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 scaled_softmax
} // end namespace fused_softmax
} // end namespace multihead_attn

PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
  m.def("forward", 
        &multihead_attn::fused_softmax::scaled_softmax::fwd, 
	"Self Multihead Attention scaled, softmax -- Forward.");
  m.def("backward", 
        &multihead_attn::fused_softmax::scaled_softmax::bwd,
	"Self Multihead Attention scaled, softmax -- Backward.");
}