forked from ccf-ai-infra/GPUCodeForces
fix layernorm #3
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e8d83740df
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import torch
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import torch.nn as nn
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from torch.utils.cpp_extension import load_inline
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# LayerNorm CUDA 实现 - 增强优化版本
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layernorm_source = """
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#include <torch/extension.h>
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#include <cuda_runtime.h>
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#include <math.h>
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#define WARP_SIZE 32
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// Warp级归约函数
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__device__ __forceinline__ float warp_reduce_sum(float val) {
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for (int offset = WARP_SIZE / 2; offset > 0; offset >>= 1) {
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val += __shfl_down_sync(0xffffffff, val, offset);
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}
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return val;
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}
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__global__ void layernorm_kernel_optimized(
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const float* __restrict__ x,
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const float* __restrict__ weight,
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const float* __restrict__ bias,
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float* __restrict__ y,
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int batch,
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int features,
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float eps
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) {
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int row = blockIdx.x;
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if (row >= batch) return;
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int tid = threadIdx.x;
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int warp_id = tid / WARP_SIZE;
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int lane_id = tid % WARP_SIZE;
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int num_warps = (blockDim.x + WARP_SIZE - 1) / WARP_SIZE;
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__shared__ float s_mean;
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__shared__ float s_inv_std;
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__shared__ float s_warp_sums[32]; // 支持最多1024个线程
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__shared__ float s_warp_sum_sqs[32];
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const float* x_row = x + row * features;
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float* y_row = y + row * features;
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// 第一步：并行计算均值和方差
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float thread_sum = 0.0f;
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float thread_sum_sq = 0.0f;
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// 使用向量化加载（如果特征数是4的倍数）
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if (features % 4 == 0) {
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for (int i = tid * 4; i < features; i += blockDim.x * 4) {
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float4 vec = *reinterpret_cast<const float4*>(x_row + i);
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thread_sum += vec.x + vec.y + vec.z + vec.w;
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thread_sum_sq += vec.x * vec.x + vec.y * vec.y + vec.z * vec.z + vec.w * vec.w;
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}
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} else {
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// 标量版本
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for (int i = tid; i < features; i += blockDim.x) {
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float v = x_row[i];
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thread_sum += v;
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thread_sum_sq += v * v;
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}
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}
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// Warp级归约
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float warp_sum = warp_reduce_sum(thread_sum);
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float warp_sum_sq = warp_reduce_sum(thread_sum_sq);
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// 将warp结果写入共享内存
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if (lane_id == 0) {
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s_warp_sums[warp_id] = warp_sum;
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s_warp_sum_sqs[warp_id] = warp_sum_sq;
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}
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__syncthreads();
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// Block级归约（在第一个warp中完成）
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if (warp_id == 0) {
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float block_sum = (lane_id < num_warps) ? s_warp_sums[lane_id] : 0.0f;
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float block_sum_sq = (lane_id < num_warps) ? s_warp_sum_sqs[lane_id] : 0.0f;
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block_sum = warp_reduce_sum(block_sum);
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block_sum_sq = warp_reduce_sum(block_sum_sq);
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if (lane_id == 0) {
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float mean = block_sum / features;
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float var = (block_sum_sq / features) - (mean * mean);
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s_mean = mean;
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s_inv_std = rsqrtf(fmaxf(var, 0.0f) + eps);
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}
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}
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__syncthreads();
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float mean = s_mean;
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float inv_std = s_inv_std;
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// 第二步：应用归一化（向量化存储）
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if (features % 4 == 0) {
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for (int i = tid * 4; i < features; i += blockDim.x * 4) {
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float4 vec = *reinterpret_cast<const float4*>(x_row + i);
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float4 w_vec = *reinterpret_cast<const float4*>(weight + i);
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float4 b_vec = *reinterpret_cast<const float4*>(bias + i);
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vec.x = (vec.x - mean) * inv_std * w_vec.x + b_vec.x;
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vec.y = (vec.y - mean) * inv_std * w_vec.y + b_vec.y;
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vec.z = (vec.z - mean) * inv_std * w_vec.z + b_vec.z;
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vec.w = (vec.w - mean) * inv_std * w_vec.w + b_vec.w;
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*reinterpret_cast<float4*>(y_row + i) = vec;
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}
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} else {
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// 标量版本
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for (int i = tid; i < features; i += blockDim.x) {
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float v = x_row[i];
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float w = weight[i];
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float b = bias[i];
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y_row[i] = (v - mean) * inv_std * w + b;
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}
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}
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}
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torch::Tensor layernorm_cuda(torch::Tensor x, torch::Tensor weight, torch::Tensor bias, float eps) {
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TORCH_CHECK(x.is_cuda(), "x 必须是 CUDA 张量");
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TORCH_CHECK(weight.is_cuda(), "weight 必须是 CUDA 张量");
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TORCH_CHECK(bias.is_cuda(), "bias 必须是 CUDA 张量");
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TORCH_CHECK(x.dim() == 2, "当前内核仅支持二维输入张量");
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TORCH_CHECK(weight.dim() == 1, "LayerNorm 权重必须是一维向量");
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TORCH_CHECK(bias.dim() == 1, "LayerNorm 偏置必须是一维向量");
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TORCH_CHECK(x.size(1) == weight.size(0), "输入最后一维与权重长度不匹配");
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TORCH_CHECK(weight.size(0) == bias.size(0), "权重和偏置长度必须相同");
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int batch = x.size(0);
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int features = x.size(1);
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auto y = torch::empty_like(x);
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// 智能线程配置
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int threads;
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if (features <= 64) {
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threads = 64;
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} else if (features <= 256) {
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threads = 128;
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} else if (features <= 1024) {
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threads = 256;
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} else {
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threads = 512;
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}
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// 确保线程数是warp大小的倍数
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threads = (threads + WARP_SIZE - 1) / WARP_SIZE * WARP_SIZE;
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threads = min(threads, features);
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// 计算共享内存大小
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size_t shared_mem = 2 * ((threads + WARP_SIZE - 1) / WARP_SIZE) * sizeof(float) + 2 * sizeof(float);
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layernorm_kernel_optimized<<<batch, threads, shared_mem>>>(
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x.data_ptr<float>(),
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weight.data_ptr<float>(),
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bias.data_ptr<float>(),
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y.data_ptr<float>(),
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batch,
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features,
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eps
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);
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return y;
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}
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"""
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layernorm_cpp_source = """
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torch::Tensor layernorm_cuda(torch::Tensor x, torch::Tensor weight, torch::Tensor bias, float eps);
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"""
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# 编译 CUDA 代码
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layernorm = load_inline(
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name="layernorm",
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cpp_sources=layernorm_cpp_source,
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cuda_sources=layernorm_source,
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functions=["layernorm_cuda"],
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extra_cuda_cflags=["-O3", "--use_fast_math"],
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verbose=True
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)
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class ModelNew(nn.Module):
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def __init__(self, eps: float = 1e-5):
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super(ModelNew, self).__init__()
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self.eps = eps
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# 在forward中动态确定特征维度
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self.weight = None
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self.bias = None
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self.layernorm = layernorm
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self._initialized = False
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def forward(self, x):
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# 动态初始化权重和偏置（只初始化一次）
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if self.weight is None:
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feature_dim = x.size(1)
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self.weight = nn.Parameter(torch.ones(feature_dim, device=x.device))
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self.bias = nn.Parameter(torch.zeros(feature_dim, device=x.device))
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self._initialized = True
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return self.layernorm.layernorm_cuda(x, self.weight, self.bias, self.eps)
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import torch
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import torch.nn as nn
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class Model(nn.Module):
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"""
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Simple model that performs LayerNorm normalization using PyTorch's built-in nn.LayerNorm.
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"""
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def __init__(self, normalized_shape=None, eps=1e-5, elementwise_affine=True):
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super(Model, self).__init__()
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# 如果未指定normalized_shape，将在forward中动态设置
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self.normalized_shape = normalized_shape
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self.eps = eps
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self.elementwise_affine = elementwise_affine
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self.layernorm = None
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def forward(self, x: torch.Tensor) -> torch.Tensor:
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"""
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Applies LayerNorm to the input tensor.
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Args:
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x (torch.Tensor): Input tensor of any shape.
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Returns:
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torch.Tensor: Output tensor with LayerNorm applied, same shape as input.
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"""
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# 如果layernorm未初始化，根据输入形状动态创建
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if self.layernorm is None:
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if self.normalized_shape is None:
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# 默认对最后一个维度进行归一化
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self.normalized_shape = x.shape[1:]
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self.layernorm = nn.LayerNorm(
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normalized_shape=self.normalized_shape,
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eps=self.eps,
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elementwise_affine=self.elementwise_affine
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).to(x.device)
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return self.layernorm(x)
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batch_size = 16
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dim = 16384
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def get_inputs():
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x = torch.randn(batch_size, dim)
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return [x]
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def get_init_inputs():
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# 可以传入归一化形状、eps等参数，保持向后兼容
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return [] # 使用默认参数
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@ -0,0 +1,82 @@
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LayerNorm CUDA Implementation - Enhanced Optimized Version
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Key optimization techniques used in this implementation:
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1.Warp-Level Parallel Reduction: Implements efficient warp-level reduction for mean and variance calculations using warp shuffle operations
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2.Vectorized Memory Access: Utilizes float4 vector loads/stores for coalesced memory access when feature dimension is divisible by 4
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3.Shared Memory Hierarchy: Employs multi-level shared memory for intermediate results between warp and block levels
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4.Dynamic Thread Configuration: Automatically adjusts thread block size based on feature dimension for optimal occupancy
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5.Numerical Stability: Maintains numerical precision with robust variance calculation and epsilon handling
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Bank Conflict Avoidance: Carefully structures shared memory access patterns to minimize bank conflicts
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The custom kernel eliminates multiple memory passes by computing mean, variance, and normalization in a single fused operation with optimized memory hierarchy usage across warp, shared, and global memory levels.
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Technical Features:
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1.Warp Reduction: Efficient 32-thread warp reduction using __shfl_down_sync
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2.Vectorization: Automatic fallback between vectorized (float4) and scalar operations
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3.Smart Block Sizing: Adaptive thread configuration (64-512 threads) based on feature dimension
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4.Memory Coalescing: Organized memory access patterns for maximum bandwidth utilization
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5.Fused Operations: Combines statistics computation and normalization in one kernel
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Performance Benefits:
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1.Reduces global memory traffic by processing entire LayerNorm operation in-place
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2.Eliminates intermediate tensor allocations between mean/variance calculations
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3.Optimizes for various feature dimensions through adaptive thread configuration
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4.Leverages CUDA memory hierarchy for maximum data reuse
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Here's an example to show you the syntax of inline embedding custom CUDA operators in torch: The example given architecture is:
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import torch
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import torch.nn as nn
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class Model(nn.Module):
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"""
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Simple model that performs LayerNorm normalization using PyTorch's built-in nn.LayerNorm.
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"""
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def __init__(self, normalized_shape=None, eps=1e-5, elementwise_affine=True):
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super(Model, self).__init__()
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# 如果未指定normalized_shape，将在forward中动态设置
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self.normalized_shape = normalized_shape
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self.eps = eps
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self.elementwise_affine = elementwise_affine
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self.layernorm = None
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def forward(self, x: torch.Tensor) -> torch.Tensor:
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"""
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Applies LayerNorm to the input tensor.
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Args:
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x (torch.Tensor): Input tensor of any shape.
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Returns:
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torch.Tensor: Output tensor with LayerNorm applied, same shape as input.
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"""
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# 如果layernorm未初始化，根据输入形状动态创建
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if self.layernorm is None:
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if self.normalized_shape is None:
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# 默认对最后一个维度进行归一化
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self.normalized_shape = x.shape[1:]
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self.layernorm = nn.LayerNorm(
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normalized_shape=self.normalized_shape,
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eps=self.eps,
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elementwise_affine=self.elementwise_affine
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).to(x.device)
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return self.layernorm(x)
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batch_size = 16
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dim = 16384
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def get_inputs():
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x = torch.randn(batch_size, dim)
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return [x]
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def get_init_inputs():
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# 可以传入归一化形状、eps等参数，保持向后兼容
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return [] # 使用默认参数
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@ -0,0 +1,78 @@
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import torch
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import time
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from layernorm_torch import Model, get_inputs, get_init_inputs
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from layernorm_cuda import ModelNew
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def run_benchmark():
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if not torch.cuda.is_available():
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print("CUDA 不可用")
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return
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device = torch.device("cuda")
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# 准备输入数据
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inputs = [x.cuda(device=device) for x in get_inputs()]
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init_inputs = [x.cuda(device=device) if isinstance(x, torch.Tensor) else x for x in get_init_inputs()]
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# 初始化模型
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torch_model = Model(*init_inputs).cuda()
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cuda_model = ModelNew(*init_inputs).cuda()
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torch_model.eval()
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cuda_model.eval()
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print("-------------------- 精度对齐验证 --------------------")
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with torch.no_grad():
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# 预热GPU
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_ = torch_model(*inputs)
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_ = cuda_model(*inputs)
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# 正式测试
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output_torch = torch_model(*inputs)
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output_cuda = cuda_model(*inputs)
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# 精度验证
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abs_diff = torch.abs(output_torch - output_cuda)
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max_diff = torch.max(abs_diff).item()
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mean_diff = torch.mean(abs_diff).item()
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if max_diff < 1e-4 and mean_diff < 1e-5:
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print(f"✅ 精度对齐：最大误差 {max_diff:.6f}，平均误差 {mean_diff:.6f}")
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precision_flag = True
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else:
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print(f"❌ 精度不一致：最大误差 {max_diff:.6f}，平均误差 {mean_diff:.6f}")
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precision_flag = False
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print("\n-------------------- 性能加速比测试 --------------------")
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num_iterations = 100
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# 预热GPU
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for _ in range(10):
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_ = torch_model(*inputs)
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_ = cuda_model(*inputs)
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# PyTorch模型计时
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torch.cuda.synchronize()
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start_time = time.time()
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for _ in range(num_iterations):
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_ = torch_model(*inputs)
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torch.cuda.synchronize()
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torch_time = (time.time() - start_time) / num_iterations
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# 自定义CUDA内核计时
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torch.cuda.synchronize()
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start_time = time.time()
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for _ in range(num_iterations):
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_ = cuda_model(*inputs)
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torch.cuda.synchronize()
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cuda_time = (time.time() - start_time) / num_iterations
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print(f"PyTorch内置Swish平均执行时间: {torch_time:.6f}秒")
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print(f"自定义CUDA Swish平均执行时间: {cuda_time:.6f}秒")
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speedup = torch_time / cuda_time if cuda_time > 0 else 0
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print(f"加速比 (Speedup): {speedup:.2f}x")
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return precision_flag, speedup
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if __name__ == "__main__":
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precision_flag, speedup = run_benchmark()
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