flash-attention/csrc/flash_attn/src/fmha.h

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#pragma once

#include <cuda.h>
#include <vector>

#ifdef OLD_GENERATOR_PATH
#include <ATen/CUDAGeneratorImpl.h>
#else
#include <ATen/cuda/CUDAGeneratorImpl.h>
#endif

#include <ATen/cuda/CUDAGraphsUtils.cuh>

#include <fmha_utils.h>


constexpr int TOTAL_DIM = 0;
constexpr int THREE_DIM = 1;
constexpr int H_DIM = 2;
constexpr int D_DIM = 3;

////////////////////////////////////////////////////////////////////////////////////////////////////

struct Qkv_params {
    // The QKV matrices.
    void * __restrict__ qkv_ptr;

    // The stride between rows of the Q, K and V matrices.
    // size_t qkv_stride_in_elts;
    // size_t qkv_stride_in_bytes;
    // TD [2022-04-16]: We're using 32-bit indexing to save registers.
    // The code probably won't work for arrays larger than 2GB.
    uint32_t qkv_stride_in_elts;
    uint32_t qkv_stride_in_bytes;

    // The number of heads.
    int h;
};

////////////////////////////////////////////////////////////////////////////////////////////////////

struct Fused_multihead_attention_fprop_params : public Qkv_params {

    // The dQKV matrices.
    void * __restrict__ dqkv_ptr;

    // Temporary for dKV.
    void * __restrict__ dkv_ptr;

    // The O matrix (output).
    void * __restrict__ o_ptr;

    // The stride between rows of O.
    // size_t o_stride_in_elts;
    // size_t o_stride_in_bytes;
    uint32_t o_stride_in_elts;
    uint32_t o_stride_in_bytes;

    // The pointer to the O_tmp matrix, which holds O intermediate value during
    // the loop;
    void *__restrict__ o_tmp_ptr;

    // The dO matrix .
    void * __restrict__ do_ptr;

    // The pointer to the S matrix, overwritten by the dP matrix (bwd).
    void * __restrict__ s_ptr;
    // The stride between rows of the S matrix.
    // int64_t s_stride_in_bytes;
    uint32_t s_stride_in_bytes;

    // The pointer to the softmax sum.
    void * __restrict__ softmax_lse_ptr;

    // The pointer to the softmax d sum.
    void * __restrict__ dsoftmax_sum;

    // The dimensions.
    int b, s, d;

    // The scaling factors for the kernel.
    float scale_bmm1f;
    uint32_t scale_bmm1, scale_softmax, scale_bmm2;

    // array of length b+1 holding starting offset of each sequence.
    int * __restrict__ cu_seqlens;

    int *__restrict__ blockmask;

    // The dropout probability (probability of keeping an activation).
    float p_dropout;
    uint32_t p_dropout_in_uint;
    uint16_t p_dropout_in_uint16_t;

    // Scale factor of 1 / (1 - p_dropout).
    float rp_dropout;

    // Scale factor of 1 / (1 - p_dropout), in half2.
    uint32_t scale_dropout;

    // Random state.
    at::PhiloxCudaState philox_args;

    bool is_causal;
};

////////////////////////////////////////////////////////////////////////////////////////////////////

template<typename Kernel_params> 
struct Launch_params{
    Launch_params(cudaDeviceProp * props_,
                  cudaStream_t stream_,
                  bool is_dropout_,
                  bool return_softmax_)
        : elts_per_thread(0)
        , props(props_)
        , stream(stream_)
        , is_dropout(is_dropout_)
        , return_softmax(return_softmax_) {
    }

    size_t elts_per_thread;

    cudaDeviceProp * props;

    cudaStream_t stream;

    bool is_dropout;
    bool return_softmax;

    Kernel_params params;
    int num_full_heads;
    int num_main_groups;
    int heads_last_wave;
    int main_steps;
    int rest_steps;
};

////////////////////////////////////////////////////////////////////////////////////////////////////

void run_fmha_fp16_sm80(Launch_params<Fused_multihead_attention_fprop_params> &launch_params, const bool configure);

void run_fmha_dgrad_fp16_sm80(const Fused_multihead_attention_fprop_params &params, cudaStream_t stream);

void run_fmha_block_fp16_sm80(Launch_params<Fused_multihead_attention_fprop_params> &launch_params, const bool configure);

void run_fmha_block_dgrad_fp16_sm80(const Fused_multihead_attention_fprop_params &params, cudaStream_t stream);