forked from ccf-ai-infra/GPUCodeForces
Merge pull request 'finish GumbelCDF #82' (#701) from hli28146/GPUCodeForces:h82 into main
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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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cpp_source = """
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#include <torch/extension.h>
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torch::Tensor gumbel_cdf_cuda_forward(const torch::Tensor& input);
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"""
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cuda_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 BLOCK_SIZE 256
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struct __align__(16) Float4 {
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float x, y, z, w;
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};
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// Gumbel CDF: exp(-exp(-x))
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__device__ __forceinline__ float compute_gumbel_cdf(float x) {
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// Clamp to prevent exp(-x) overflow for large negative x
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float neg_x = fminf(-x, 80.0f);
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float inner_exp = __expf(neg_x);
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return __expf(-inner_exp);
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}
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__global__ void gumbel_cdf_kernel(
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float* __restrict__ output,
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const float* __restrict__ input,
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const int n)
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{
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const int idx = blockIdx.x * blockDim.x + threadIdx.x;
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const int vec_n = n / 4;
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int i = idx;
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const int stride = blockDim.x * gridDim.x;
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for (; i < vec_n; i += stride) {
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Float4 in_vec = reinterpret_cast<const Float4*>(input)[i];
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Float4 out_vec;
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out_vec.x = compute_gumbel_cdf(in_vec.x);
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out_vec.y = compute_gumbel_cdf(in_vec.y);
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out_vec.z = compute_gumbel_cdf(in_vec.z);
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out_vec.w = compute_gumbel_cdf(in_vec.w);
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reinterpret_cast<Float4*>(output)[i] = out_vec;
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}
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int start_scalar = vec_n * 4;
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int global_tid = blockIdx.x * blockDim.x + threadIdx.x;
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int total_threads = gridDim.x * gridDim.x;
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int current_idx = start_scalar + global_tid;
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while (current_idx < n) {
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output[current_idx] = compute_gumbel_cdf(input[current_idx]);
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current_idx += total_threads;
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}
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}
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torch::Tensor gumbel_cdf_cuda_forward(const torch::Tensor& input) {
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TORCH_CHECK(input.is_cuda(), "Input must be a CUDA tensor");
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TORCH_CHECK(input.is_contiguous(), "Input must be contiguous");
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const int n = input.numel();
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auto output = torch::empty_like(input);
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const int vec_n = n / 4;
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const int grid_size = (vec_n + BLOCK_SIZE - 1) / BLOCK_SIZE;
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int final_grid = (grid_size < 1) ? 1 : grid_size;
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if (final_grid > 65535) final_grid = 65535;
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gumbel_cdf_kernel<<<final_grid, BLOCK_SIZE>>>(
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output.data_ptr<float>(),
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input.data_ptr<float>(),
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n
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);
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return output;
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}
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"""
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gumbel_cdf_op_module = load_inline(
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name='gumbel_cdf_op',
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cpp_sources=cpp_source,
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cuda_sources=cuda_source,
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functions=['gumbel_cdf_cuda_forward'],
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verbose=False,
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extra_cuda_cflags=['-O3', '--use_fast_math']
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)
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class ModelNew(nn.Module):
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def __init__(self):
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super(ModelNew, self).__init__()
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self.op = gumbel_cdf_op_module
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def forward(self, input_tensor: torch.Tensor) -> torch.Tensor:
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return self.op.gumbel_cdf_cuda_forward(input_tensor.contiguous())
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import torch
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import torch.nn as nn
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BATCH_SIZE = 4096
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HIDDEN_DIM = 4096
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SHAPE = (BATCH_SIZE, HIDDEN_DIM)
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class GumbelCDF(nn.Module):
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"""
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Gumbel Cumulative Distribution Function (CDF).
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f(x) = exp(-exp(-x))
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"""
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def __init__(self, clamp_val=80.0):
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super(GumbelCDF, self).__init__()
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self.clamp_val = clamp_val
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def forward(self, x: torch.Tensor) -> torch.Tensor:
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neg_x = torch.clamp(-x, max=self.clamp_val)
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inner_exp = torch.exp(neg_x)
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return torch.exp(-inner_exp)
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class Model(nn.Module):
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def __init__(self):
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super(Model, self).__init__()
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self.act = GumbelCDF()
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def forward(self, x):
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return self.act(x)
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def get_inputs():
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# 覆盖正负区间
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input_tensor = torch.randn(SHAPE, dtype=torch.float32) * 20.0
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return [input_tensor.contiguous()]
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def get_init_inputs():
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return []
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Write a custom CUDA kernel to optimize the `Gumbel CDF` as an activation function.
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Formula: f(x) = exp(-exp(-x))
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Problem Analysis:
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1. Computationally Intensive: This operation involves a double exponential, which is arithmetically heavy for an element-wise activation.
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2. Memory Bottleneck: A standard PyTorch implementation `torch.exp(-torch.exp(-x))` chains three separate kernels, creating two intermediate tensors and high memory traffic.
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3. Numerical Stability: The inner `exp(-x)` can overflow if `x` is a large negative number.
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Optimization Strategy: Fused Element-wise Kernel with Vectorization
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1. One-Thread-per-Element: Map each element to a CUDA thread.
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2. Vectorized Loads (float4): Use `float4` to process 128 bits per memory transaction.
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3. Fused Stable Math:
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- For each element `x`, first compute `inner_val = -x`.
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- Clamp `inner_val` to a safe upper bound (e.g., 80.0) to prevent `exp` overflow.
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- Compute `exp1 = __expf(clamped_inner_val)`.
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- Compute `result = __expf(-exp1)`.
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- All steps are fused in registers.
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4. One-Pass: Fuse all logic into a single read-compute-write kernel.
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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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```python
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import torch
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import torch.nn as nn
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BATCH_SIZE = 4096
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HIDDEN_DIM = 4096
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SHAPE = (BATCH_SIZE, HIDDEN_DIM)
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class GumbelCDF(nn.Module):
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"""
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Gumbel Cumulative Distribution Function (CDF).
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f(x) = exp(-exp(-x))
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"""
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def __init__(self, clamp_val=80.0):
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super(GumbelCDF, self).__init__()
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self.clamp_val = clamp_val
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def forward(self, x: torch.Tensor) -> torch.Tensor:
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neg_x = torch.clamp(-x, max=self.clamp_val)
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inner_exp = torch.exp(neg_x)
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return torch.exp(-inner_exp)
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class Model(nn.Module):
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def __init__(self):
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super(Model, self).__init__()
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self.act = GumbelCDF()
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def forward(self, x):
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return self.act(x)
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def get_inputs():
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# 覆盖正负区间
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input_tensor = torch.randn(SHAPE, dtype=torch.float32) * 20.0
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return [input_tensor.contiguous()]
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def get_init_inputs():
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return []
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###########################################################
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# 性能和精度验证程序
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###########################################################
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import torch
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import torch.nn as nn
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import time
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from GumbelCDF_torch import Model,get_inputs,get_init_inputs
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from GumbelCDF_cuda import ModelNew
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def run_benchmark():
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# 检查 CUDA 是否可用
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if not torch.cuda.is_available():
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print("CUDA 不可用，请确保您有可用的 NVIDIA GPU 并已正确安装 PyTorch CUDA 版本。")
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return
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else:
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device = torch.device("cuda")
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# 初始化模型
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init_inputs = get_init_inputs()
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init_inputs = [
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x.cuda(device=device) if isinstance(x, torch.Tensor) else x for x in init_inputs
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]
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inputs = get_inputs()
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inputs = [
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x.cuda(device=device) if isinstance(x, torch.Tensor) else x for x in inputs
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]
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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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output_torch = torch_model( *inputs)
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output_cuda = cuda_model(*inputs)
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precision_flag = torch.allclose(output_torch, output_cuda,rtol=1e-03)
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if precision_flag:
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print("✅ 精度对齐：两个模型的输出结果非常接近。")
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else:
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print("❌ 精度不一致！")
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print("\n-------------------- 性能加速比测试 --------------------")
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num_iterations = 100
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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 torch.relu 平均执行时间: {torch_time:.6f} 秒")
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print(f"自定义 CUDA 内核 平均执行时间: {cuda_time:.6f} 秒")
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speedup = 0
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if cuda_time > 0:
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speedup = torch_time / cuda_time
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print(f"加速比 (Speedup): {speedup:.2f}x")
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else:
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print("CUDA 内核执行时间为0，无法计算加速比。")
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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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