将 cuda 数组传递给 thrust::inclusive_scan

Question

我可以将 inclusive_scan 用于 cpu 上的数组，但是否可以使用 gpu 上的数组来实现？（注释是我知道有效但我不需要的方式）。或者，还有其他简单的方法可以对设备内存中的数组执行包容性扫描吗？

代码：

#include <stdio.h>
#include <stdlib.h> /* for rand() */
#include <unistd.h> /* for getpid() */
#include <time.h> /* for time() */
#include <math.h>
#include <assert.h>
#include <iostream>
#include <ctime>
  #include <thrust/scan.h>
#include <cuda.h>



#ifdef DOUBLE
 #define REAL double
 #define MAXT 256
#else
 #define REAL float
 #define MAXT 512
#endif

#ifndef MIN
#define MIN(x,y) ((x < y) ? x : y)
#endif

using namespace std;

bool errorAsk(const char *s="n/a")
{
cudaError_t err=cudaGetLastError();
if(err==cudaSuccess)
    return false;
printf("CUDA error [%s]: %s\n",s,cudaGetErrorString(err));
return true;
};

double *fillArray(double *c_idata,int N,double constant) {
    int n;
    for (n = 0; n < N; n++) {
            c_idata[n] = constant*floor(drand48()*10);

    }
return c_idata;
}

int main(int argc,char *argv[])
{
    int N,blocks,threads;
    N = 100;
    threads=MAXT;
    blocks=N/threads+(N%threads==0?0:1);

    double *c_data,*g_data;

    c_data = new double[N];
    c_data = fillArray(c_data,N,1);
    cudaMalloc(&g_data,N*sizeof(double));

    cudaMemcpy(g_data,c_data,N*sizeof(double),cudaMemcpyHostToDevice);
    thrust::inclusive_scan(g_data, g_data + N, g_data); // in-place scan
    cudaMemcpy(c_data,g_data,N*sizeof(double),cudaMemcpyDeviceToHost);

//        thrust::inclusive_scan(c_data, c_data + N, c_data); // in-place scan

    for(int i = 0; i < N; i++) {
            cout<<c_data[i]<<endl;
    }
}

Answer 1

如果您阅读 thrust quick start guide，您会发现一个处理 "raw" 设备数据的建议：使用 thrust::device_ptr:

You may wonder what happens when a "raw" pointer is used as an argument to a Thrust function. Like the STL, Thrust permits this usage and it will dispatch the host path of the algorithm. If the pointer in question is in fact a pointer to device memory then you'll need to wrap it with thrust::device_ptr before calling the function.

要修复您的代码，您需要

#include <thrust/device_ptr.h>

并用以下两行替换现有的对 thrust::inclusive_scan 的调用：

thrust::device_ptr<double> g_ptr = thrust::device_pointer_cast(g_data);
thrust::inclusive_scan(g_ptr, g_ptr + N, g_ptr); // in-place scan

另一种方法是使用 thrust execution policies 并像这样修改您的调用：

thrust::inclusive_scan(thrust::device, g_data, g_data + N, g_data);

还有其他各种可能性。

将 cuda 数组传递给 thrust::inclusive_scan

Pass cuda array to thrust::inclusive_scan

cuda

thrust