llama.cpp/ggml/src/ggml-vulkan/vulkan-shaders/rms_norm_back.comp

#version 450

#include "generic_head.comp"
#include "types.comp"

#extension GL_EXT_control_flow_attributes : enable
#define BLOCK_SIZE 512

layout(local_size_x = BLOCK_SIZE, local_size_y = 1, local_size_z = 1) in;

layout (binding = 0) readonly buffer G {A_TYPE data_a[];};
layout (binding = 1) readonly buffer X {B_TYPE data_b[];};
layout (binding = 2) writeonly buffer D {D_TYPE data_d[];};

shared FLOAT_TYPE sum_xx[BLOCK_SIZE];
shared FLOAT_TYPE sum_xg[BLOCK_SIZE];

void main() {
    const uint row = gl_WorkGroupID.z * 262144 + gl_WorkGroupID.y * 512 + gl_WorkGroupID.x;
    const uint tid = gl_LocalInvocationID.x;

    // Compute derivative of x[i]/norm(x) = g[i]/norm(x) - x[i] dot(x,g)/KX / norm(x)^1.5

    // partial sums for thread in warp
    sum_xx[tid] = FLOAT_TYPE(0.0f);
    sum_xg[tid] = FLOAT_TYPE(0.0f);

    [[unroll]] for (uint col = tid; col < p.KX; col += BLOCK_SIZE) {
        const FLOAT_TYPE gi = FLOAT_TYPE(data_a[row*p.KX + col]);
        const FLOAT_TYPE xi = FLOAT_TYPE(data_b[row*p.KX + col]);
        sum_xx[tid] += xi * xi;
        sum_xg[tid] += xi * gi;
    }

    // sum up partial sums and write back result
    barrier();
    [[unroll]] for (int s = BLOCK_SIZE / 2; s > 0; s >>= 1) {
        if (tid < s) {
            sum_xx[tid] += sum_xx[tid + s];
            sum_xg[tid] += sum_xg[tid + s];
        }
        barrier();
    }

    const FLOAT_TYPE eps = FLOAT_TYPE(p.param1);
    const FLOAT_TYPE mean = sum_xx[0] / FLOAT_TYPE(p.KX);
    const FLOAT_TYPE scale_g = inversesqrt(mean + eps);
    const FLOAT_TYPE scale_x = -scale_g * sum_xg[0] / (sum_xx[0] + FLOAT_TYPE(p.KX) * eps);

    [[unroll]] for (uint col = tid; col < p.KX; col += BLOCK_SIZE) {
        data_d[row*p.KX + col] = D_TYPE(
            scale_g * FLOAT_TYPE(data_a[row*p.KX + col]) +
            scale_x * FLOAT_TYPE(data_b[row*p.KX + col]));
    }
}