c++ - CUDA Thrust Min_Element 结果等于 0

Question

对 CUDA 和 C++ 非常陌生，但一直在努力解决我注意到的一些问题。我想生成最小的数字以及 CUDA 中的索引。目前我有

    __global__ void updateGB2(Particle *dev_p) {
    int i = threadIdx.x + blockIdx.x *blockDim.x;

    globalB[i] = dev_p[i].localBest;

    double *result = thrust::min_element(thrust::device,globalB, globalB + pSize);
    printf("%lf", result);
}

并且正在调用此方法，但结果仅打印 0.0000。我可能遗漏了一些使用推力的信息，但根据我阅读的信息，我不确定还能做什么。globalB 定义为 device 并且 Particle 从 CPU 传递到 GPU。

Answer 1

引自推力documentation

min_element finds the smallest element in the range [first, last). It returns the first iterator i in [first, last) such that no other iterator in [first, last) points to a value smaller than *i.

在您的代码中，这意味着 result 是一个指针，必须解除引用才能访问最小值。一个完整的例子:

#include <cstdio>
#include <thrust/device_vector.h>
#include <thrust/extrema.h>
#include <thrust/copy.h>

__global__ void updateGB2(double *data, int pSize) {
    int i = threadIdx.x + blockIdx.x *blockDim.x;

    double* globalB = data + (i * pSize);
    double* result = thrust::min_element(thrust::device, globalB, globalB + pSize);
    printf("%d %lf\n", i, *result);
}

int main() 
{
    const int pSize = 16;
    const int Nvectors = 32;
    const int Nvals = Nvectors * pSize;

    {
        thrust::device_vector<double> dv(Nvals);

        thrust::counting_iterator<double> counter(10);
        thrust::copy(counter, counter+Nvals, dv.begin());

        double* d_h = thrust::raw_pointer_cast(dv.data());
        updateGB2<<<1, Nvectors>>>(d_h, pSize);
        cudaDeviceSynchronize();
    }
    cudaDeviceReset();

    return 0;
}

编译和运行如下:

$ nvcc -arch=sm_52 -o thrustdevice thrustdevice.cu 
$ ./thrustdevice 
0 10.000000
1 26.000000
2 42.000000
3 58.000000
4 74.000000
5 90.000000
6 106.000000
7 122.000000
8 138.000000
9 154.000000
10 170.000000
11 186.000000
12 202.000000
13 218.000000
14 234.000000
15 250.000000
16 266.000000
17 282.000000
18 298.000000
19 314.000000
20 330.000000
21 346.000000
22 362.000000
23 378.000000
24 394.000000
25 410.000000
26 426.000000
27 442.000000
28 458.000000
29 474.000000
30 490.000000
31 506.000000