ggml/src/ggml-vulkan/vulkan-shaders/flash_attn.comp

#version 450

#extension GL_EXT_control_flow_attributes : enable
#extension GL_EXT_shader_16bit_storage : require

#extension GL_EXT_shader_explicit_arithmetic_types_float16 : require
#extension GL_EXT_shader_explicit_arithmetic_types_int32 : require

#extension GL_KHR_shader_subgroup_shuffle : enable

#include "types.comp"
#include "flash_attn_base.comp"

const uint32_t D_per_thread = D / D_split;

const uint32_t cols_per_iter = WorkGroupSize / D_split;
const uint32_t cols_per_thread = Bc / cols_per_iter;


layout (binding = 0) readonly buffer Q {float data_q[];};
layout (binding = 0) readonly buffer QV4 {vec4 data_qv4[];};
layout (binding = 1) readonly buffer K {float16_t data_k[];};
layout (binding = 1) readonly buffer KV4 {f16vec4 data_kv4[];};
layout (binding = 2) readonly buffer V {float16_t data_v[];};
layout (binding = 2) readonly buffer VV4 {f16vec4 data_vv4[];};
layout (binding = 3) readonly buffer M {float16_t data_m[];};

// Store the output when doing grouped query attention.
// Rows index by Q's dimension 2, and the first N rows are valid.
D_TYPE perElemOpGqaStore(const in uint32_t r, const in uint32_t c, const in D_TYPE elem, const in uint32_t o_offset, const in uint32_t iq2, const in uint32_t N)
{
    uint32_t offset = (iq2 + r) * D + c;
    data_o[o_offset + offset] = D_TYPE(elem);
    return elem;
}

shared FLOAT_TYPE tmpsh[WorkGroupSize];
shared vec4 tmpshv4[WorkGroupSize];

shared float masksh[Bc][Br];
shared vec4 Qf[Br][D / 4];

void main() {
#ifdef NEEDS_INIT_IQ_SHMEM
    init_iq_shmem(gl_WorkGroupSize);
#endif

    init_indices();

    const uint32_t tid = gl_LocalInvocationIndex;
    const uint32_t d_tid = gl_LocalInvocationIndex % D_split;
    const uint32_t col_tid = gl_LocalInvocationIndex / D_split;

    uint32_t q_offset = (iq2*p.nb02+iq3*p.nb03) / 4;

    [[unroll]] for (uint32_t idx = 0; idx < Br * D / 4; idx += gl_WorkGroupSize.x) {
        uint32_t d = (idx + tid) % (D / 4);
        uint32_t r = (idx + tid) / (D / 4);
        if (r < Br && d < D / 4 &&
            i * Br + r < N) {
            Qf[r][d] = vec4(data_qv4[q_offset / 4 + (i * Br + r) * q_stride / 4 + d]) * p.scale;
        }
    }
    barrier();

    vec4 Of[Br][D_per_thread / 4];
    [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {
        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            Of[r][d] = vec4(0.0);
        }
    }

    float Lf[Br], Mf[Br];

    // Use -FLT_MAX/2 rather than -inf to reduce the possibility of NaNs, e.g. when computing Mold-M.
    const float NEG_FLT_MAX_OVER_2 = uintBitsToFloat(0xFEFFFFFF);

    [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
        Lf[r] = 0;
        Mf[r] = NEG_FLT_MAX_OVER_2;
    }

    float slope[Br];
    [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
        slope[r] = 1.0;
    }

    // ALiBi
    if (p.max_bias > 0.0f) {
        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            slope[r] = perElemOpComputeSlope(r, col_tid, ACC_TYPE(0), iq2);
        }
    }

#if BLOCK_SIZE > 1
    uint32_t k_offset = (ik2*p.nb12 + ik3*p.nb13) / BLOCK_BYTE_SIZE;
    uint32_t v_offset = (iv2*p.nb22 + iv3*p.nb23) / BLOCK_BYTE_SIZE;
#else
    uint32_t k_offset = (ik2*p.nb12 + ik3*p.nb13) / 2;
    uint32_t v_offset = (iv2*p.nb22 + iv3*p.nb23) / 2;
#endif

    [[dont_unroll]]
    for (uint32_t j = start_j; j < end_j; ++j) {

        float Sf[Br][cols_per_thread];
        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                Sf[r][c] = 0.0;
            }
        }


        [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
            [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {
#if BLOCK_SIZE > 1
                uint coord = (j * Bc + c * cols_per_iter + col_tid) * k_stride * BLOCK_SIZE + 4 * (d * D_split + d_tid);
                uint ib = coord / BLOCK_SIZE;
                uint iqs = (coord % BLOCK_SIZE);
                vec4 K_Tf = dequantize4(ib, iqs, k_offset, BINDING_IDX_K);
#else
                vec4 K_Tf = vec4(data_kv4[k_offset / 4 + (j * Bc + c * cols_per_iter + col_tid) * k_stride / 4 + d * D_split + d_tid]);
#endif
                [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
                    Sf[r][c] += dot(Qf[r][d * D_split + d_tid], K_Tf);
                }
            }
        }

        [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
            // Compute sum across the D_split
            [[unroll]] for (uint s = D_split / 2; s > 0; s >>= 1) {
                [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
                    Sf[r][c] += subgroupShuffleXor(Sf[r][c], s);
                }
            }
        }

        if (p.logit_softcap != 0.0f) {
            [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
                [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                    Sf[r][c] = p.logit_softcap * tanh(Sf[r][c]);
                }
            }
        }

        if (p.mask != 0) {

            [[unroll]] for (uint32_t idx = 0; idx < Bc * Br; idx += gl_WorkGroupSize.x) {
                uint32_t c = (idx + tid) % Bc;
                uint32_t r = (idx + tid) / Bc;
                if (idx + tid < Bc * Br) {
                    masksh[c][r] = float(data_m[(i * Br + r) * m_stride + (j * Bc + c)]);
                }
            }
            barrier();

            [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
                    float mvf = masksh[c * cols_per_iter + col_tid][r];

                    Sf[r][c] += slope[r]*mvf;
                }
            }
            barrier();
        }

        float rowmaxf[Br], Pf[Br][cols_per_thread], rowsumf[Br], eMf[Br], Moldf[Br];
        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            rowmaxf[r] = Sf[r][0];
            [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                rowmaxf[r] = max(rowmaxf[r], Sf[r][c]);
            }
            Moldf[r] = Mf[r];

            // M = max(rowmax, Mold)
            // P = e^(S - M)
            // eM = e^(Mold - M)
            Mf[r] = max(rowmaxf[r], Moldf[r]);
            [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                Pf[r][c] = exp(Sf[r][c] - Mf[r]);
            }
            eMf[r] = exp(Moldf[r] - Mf[r]);

            // Compute sum across row of P
            rowsumf[r] = 0.0;
            [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                rowsumf[r] += Pf[r][c];
            }

            Lf[r] = eMf[r]*Lf[r] + rowsumf[r];
        }

        [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {
            [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
                Of[r][d] = eMf[r] * Of[r][d];
            }
        }

        [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
            [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {
#if BLOCK_SIZE > 1
                uint coord = (j * Bc + c * cols_per_iter + col_tid) * v_stride * BLOCK_SIZE + 4 * (d * D_split + d_tid);
                uint ib = coord / BLOCK_SIZE;
                uint iqs = (coord % BLOCK_SIZE);
                vec4 Vf = dequantize4(ib, iqs, v_offset, BINDING_IDX_V);
#else
                vec4 Vf = vec4(data_vv4[v_offset / 4 + (j * Bc + c * cols_per_iter + col_tid) * v_stride / 4 + d * D_split + d_tid]);
#endif
                [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
                    Of[r][d] += Pf[r][c] * Vf;
                }
            }
        }

        barrier();
    }

    // reduce across threads

    [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
        float rowmaxf, eMf;

        tmpsh[tid] = Mf[r];
        // Compute max across the row
        barrier();
        [[unroll]] for (int s = int(gl_WorkGroupSize.x) / 2; s >= D_split; s >>= 1) {
            if (tid < s) {
                tmpsh[tid] = max(tmpsh[tid], tmpsh[tid + s]);
            }
            barrier();
        }
        rowmaxf = tmpsh[d_tid];
        barrier();

        float Moldf = Mf[r];

        // M = max(rowmax, Mold)
        // eM = e^(Mold - M)
        Mf[r] = max(rowmaxf, Moldf);
        eMf = exp(Moldf - Mf[r]);

        Lf[r] = eMf*Lf[r];

        tmpsh[tid] = Lf[r];

        // Compute sum across the row
        barrier();
        [[unroll]] for (int s = int(gl_WorkGroupSize.x) / 2; s >= D_split; s >>= 1) {
            if (tid < s) {
                tmpsh[tid] = tmpsh[tid] + tmpsh[tid + s];
            }
            barrier();
        }
        Lf[r] = tmpsh[d_tid];
        barrier();

        [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {

            Of[r][d] = eMf * Of[r][d];
            tmpshv4[tid] = Of[r][d];

            barrier();
            [[unroll]] for (int s = int(gl_WorkGroupSize.x) / 2; s >= D_split; s >>= 1) {
                if (tid < s) {
                    Of[r][d] += tmpshv4[tid + s];
                    tmpshv4[tid] = Of[r][d];
                }
                barrier();
            }
            Of[r][d] = tmpshv4[d_tid];
            barrier();
        }
    }


    // If there is split_k, then the split_k resolve shader does the final
    // division by L. Store the intermediate O value and per-row m and L values.
    if (p.k_num > 1) {
        uint32_t o_offset = D * p.ne1 * split_k_index;

        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            if (r < N) {
                [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {
                    [[unroll]] for (uint32_t comp = 0; comp < 4; ++comp) {
                        perElemOpGqaStore(r, 4*(d * D_split + d_tid) + comp, Of[r][d][comp], o_offset, iq2, N);
                    }
                }
            }
        }

        o_offset = D * p.ne1 * p.k_num + p.ne1 * split_k_index * 2;
        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            if (r < N) {
                perElemOpStoreCol0(r, 0u, ACC_TYPE(Lf[r]), o_offset, iq2, N);
                perElemOpStoreCol0(r, 0u, ACC_TYPE(Mf[r]), o_offset + p.ne1, iq2, N);
            }
        }

        return;
    }

    float Lfrcp[Br];
    [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
        Lfrcp[r] = 1.0 / Lf[r];
    }

    [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {
        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            Of[r][d] *= Lfrcp[r];
        }
    }

    uint32_t o_offset = iq3*p.ne2*p.ne1;

    if (p.gqa_ratio > 1) {
        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            if (r < N) {
                [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {
                    [[unroll]] for (uint32_t comp = 0; comp < 4; ++comp) {
                        perElemOpGqaStore(r, 4*(d * D_split + d_tid) + comp, Of[r][d][comp], o_offset, iq2, N);
                    }
                }
            }
        }
    } else {
        [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
            if (i * Br + r < N) {
                [[unroll]] for (uint32_t d = 0; d < D_per_thread / 4; ++d) {
                    [[unroll]] for (uint32_t comp = 0; comp < 4; ++comp) {
                        data_o[o_offset + iq2 * D + (i * Br + r) * p.ne1 * D + 4*(d * D_split + d_tid) + comp] = D_TYPE(Of[r][d][comp]);
                    }
                }
            }
        }
    }
}