并行计算CUDA DEMO

本文介绍了一个使用CUDA进行并行计算的简单示例程序,演示了如何通过CUDA实现两个整数数组的加法运算,并展示了从主机内存到GPU内存的数据传输过程。

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//并行计算CUDA DEMO
#include "cuda_runtime.h"
#include "device_launch_parameters.h"

#include <stdio.h>

cudaError_t addWithCuda(int *c, const int *a, const int *b, unsigned int size);

__global__ void addKernel(int *c, const int *a, const int *b)
{
    int i = threadIdx.x;
    c[i] = a[i] + b[i];
}

int main()
{
    const int arraySize = 5;
    const int a[arraySize] = { 1, 2, 3, 4, 5 };
    const int b[arraySize] = { 10, 20, 30, 40, 50 };
    int c[arraySize] = { 0 };

    // Add vectors in parallel.
    cudaError_t cudaStatus = addWithCuda(c, a, b, arraySize);
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "addWithCuda failed!");
        return 1;
    }

    printf("{1,2,3,4,5} + {10,20,30,40,50} = {%d,%d,%d,%d,%d}\n",
        c[0], c[1], c[2], c[3], c[4]);

    // cudaDeviceReset must be called before exiting in order for profiling and
    // tracing tools such as Nsight and Visual Profiler to show complete traces.
    cudaStatus = cudaDeviceReset();
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaDeviceReset failed!");
        return 1;
    }

    return 0;
}

// Helper function for using CUDA to add vectors in parallel.
cudaError_t addWithCuda(int *c, const int *a, const int *b, unsigned int size)
{
    int *dev_a = 0;
    int *dev_b = 0;
    int *dev_c = 0;
    cudaError_t cudaStatus;

    // Choose which GPU to run on, change this on a multi-GPU system.
    cudaStatus = cudaSetDevice(0);
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaSetDevice failed!  Do you have a CUDA-capable GPU installed?");
        goto Error;
    }

    // Allocate GPU buffers for three vectors (two input, one output)    .
    cudaStatus = cudaMalloc((void**)&dev_c, size * sizeof(int));
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaMalloc failed!");
        goto Error;
    }

    cudaStatus = cudaMalloc((void**)&dev_a, size * sizeof(int));
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaMalloc failed!");
        goto Error;
    }

    cudaStatus = cudaMalloc((void**)&dev_b, size * sizeof(int));
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaMalloc failed!");
        goto Error;
    }

    // Copy input vectors from host memory to GPU buffers.
    cudaStatus = cudaMemcpy(dev_a, a, size * sizeof(int), cudaMemcpyHostToDevice);
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaMemcpy failed!");
        goto Error;
    }

    cudaStatus = cudaMemcpy(dev_b, b, size * sizeof(int), cudaMemcpyHostToDevice);
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaMemcpy failed!");
        goto Error;
    }

    // Launch a kernel on the GPU with one thread for each element.
    addKernel<<<1, size>>>(dev_c, dev_a, dev_b);

    // Check for any errors launching the kernel
    cudaStatus = cudaGetLastError();
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "addKernel launch failed: %s\n", cudaGetErrorString(cudaStatus));
        goto Error;
    }
    
    // cudaDeviceSynchronize waits for the kernel to finish, and returns
    // any errors encountered during the launch.
    cudaStatus = cudaDeviceSynchronize();
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaDeviceSynchronize returned error code %d after launching addKernel!\n", cudaStatus);
        goto Error;
    }

    // Copy output vector from GPU buffer to host memory.
    cudaStatus = cudaMemcpy(c, dev_c, size * sizeof(int), cudaMemcpyDeviceToHost);
    if (cudaStatus != cudaSuccess) {
        fprintf(stderr, "cudaMemcpy failed!");
        goto Error;
    }

Error:
    cudaFree(dev_c);
    cudaFree(dev_a);
    cudaFree(dev_b);
    
    return cudaStatus;
}

VS2019编译时返回MSB3721时没有更多错误信息
复制编译输出到命令行运行查看出错信息
nvcc.exe -gencode=arch=compute_52,code=\"sm_52,compute_52\" --use-local-env -ccbin "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\bin\HostX86\x64" -x cu   -I"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include" -I"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\atlmfc\include" -I"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\VS\include" -I"C:\Program Files (x86)\Windows Kits\10\Include\10.0.19041.0\ucrt" -I"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\VS\UnitTest\include" -I"C:\Program Files (x86)\Windows Kits\10\Include\10.0.19041.0\um" -I"C:\Program Files (x86)\Windows Kits\10\Include\10.0.19041.0\shared" -I"C:\Program Files (x86)\Windows Kits\10\Include\10.0.19041.0\winrt" -I"C:\Program Files (x86)\Windows Kits\10\Include\10.0.19041.0\cppwinrt" -I"C:\Program Files (x86)\Windows Kits\NETFXSDK\4.8\Include\um" -I"C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v11.1\include\include" -I"C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v11.1\include\include"     --keep-dir x64\Release -maxrregcount=0  --machine 64 --compile -cudart static     -DWIN32 -DWIN64 -DNDEBUG -D_CONSOLE -D_MBCS -Xcompiler "/EHsc /W3 /nologo /O2 /Fdx64\Release\vc142.pdb /FS   /MD " -o D:\space\vsspace\TestCUDA\x64\Release\kernel.cu.obj "D:\space\vsspace\TestCUDA\TestCUDA\kernel.cu"
根据错误信息解决各种问题
输入路径改为绝对路径 $(OutDir)%(Filename)%(Extension).obj

### 实现GPU并行计算的方法 在PyTorch中实现多GPU并行计算可以通过多种方式完成,其中一种常用的方式是使用`torch.nn.DataParallel`模块。然而更推荐的是采用分布式数据并行(Distributed Data Parallel, DDP),因为DDP提供了更好的性能和灵活性[^1]。 #### 使用Distributed Data Parallel (DDP) 要利用多个GPU来加速模型训练过程中的前向传播和反向传播操作,可以按照如下方式进行: ```python import torch import torch.distributed as dist from torch.nn.parallel import DistributedDataParallel as DDP import os def setup(rank, world_size): """初始化进程组""" os.environ['MASTER_ADDR'] = 'localhost' os.environ['MASTER_PORT'] = '12355' # 初始化进程组 dist.init_process_group("nccl", rank=rank, world_size=world_size) def cleanup(): """清理进程组""" dist.destroy_process_group() class ToyModel(torch.nn.Module): def __init__(self): super(ToyModel, self).__init__() # 定义简单的线性层作为例子 self.net1 = torch.nn.Linear(10, 10).to('cuda') self.relu = torch.nn.ReLU() self.net2 = torch.nn.Linear(10, 5).to('cuda') def forward(self, x): x = self.relu(self.net1(x)) return self.net2(x) def demo_basic(rank, world_size): print(f"Running basic DDP example on rank {rank}.") setup(rank, world_size) model = ToyModel().to(rank) ddp_model = DDP(model, device_ids=[rank]) loss_fn = torch.nn.MSELoss() optimizer = torch.optim.SGD(ddp_model.parameters(), lr=0.001) outputs = ddp_model(torch.randn(20, 10).to(rank)) labels = torch.randn(20, 5).to(rank) loss_fn(outputs, labels).backward() optimizer.step() cleanup() if __name__ == "__main__": free_gpus = list(range(torch.cuda.device_count())) world_size = len(free_gpus) torch.multiprocessing.spawn(demo_basic, args=(world_size,), nprocs=world_size, join=True) ``` 这段代码展示了如何设置一个基本的分布式环境,并创建了一个玩具级别的神经网络来进行演示。通过调用`setup()`函数配置好通信参数之后,在每个进程中实例化相同的模型对象并将它们封装到`DistributedDataParallel`类里去处理跨设备间的同步问题。最后记得调用`cleanup()`释放资源。 对于拥有NVIDIA T4 GPU硬件支持的情况,可以根据具体需求调整上述脚本以适应不同的实例规格,比如单个或多个GPU每台机器上运行的任务数量等[^2]。 当涉及到推理服务时,由于这类任务通常涉及较小规模的操作且消耗较少的GPU资源,可能会遇到较低利用率的问题。此时可考虑批量处理请求的方式来提高效率[^3]。
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