candle-flash-attn-v1/kernels/fmha.h

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#pragma once

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

#include "fmha_utils.h"


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

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

struct Qkv_params {
    // The QKV matrices.
    void *__restrict__ q_ptr;
    void *__restrict__ k_ptr;
    void *__restrict__ v_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 q_row_stride_in_elts;
    uint32_t k_row_stride_in_elts;
    uint32_t v_row_stride_in_elts;
    uint32_t q_head_stride_in_elts;
    uint32_t k_head_stride_in_elts;
    uint32_t v_head_stride_in_elts;

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

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

struct FMHA_fprop_params : public Qkv_params {

    // 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_row_stride_in_elts;
    uint32_t o_head_stride_in_elts;
    uint32_t o_tmp_row_stride_in_elts;
    uint32_t o_tmp_head_stride_in_elts;

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

    // The pointer to the S matrix.
    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 dimensions.
    int b, seqlen_q, seqlen_k, d;

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

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

    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;
    float scale_bmm1_rp_dropout;

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

    // Random state.
//    at::PhiloxCudaState philox_args;
    // Pointer to the RNG seed (idx 0) and offset (idx 1).
//    uint64_t * rng_state;

    bool is_bf16;
    bool is_causal;

    int num_splits; // How many SMs per attention matrix.
};

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

template<typename Kernel_params>
struct Launch_params{
    size_t elts_per_thread;

    int multi_processor_count;

    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_fwd_hdim32(Launch_params<FMHA_fprop_params> &launch_params);
void run_fmha_fwd_hdim64(Launch_params<FMHA_fprop_params> &launch_params);
void run_fmha_fwd_hdim128(Launch_params<FMHA_fprop_params> &launch_params);