设备内存中的多个指针，用于CUDA中的单个分配数组

Question

I am wondering if there is it possible to setup multiple pointers to single data already allocated in memory? the reason i am asking this is because i was implementing lexographical sorting with gpu with the help of thrust vectors (and failed miserably in terms of time)

for example i am trying to acheive equivalent of these c++ statments

unsigned int * pword;      //setting up the array of memory for permutations of word
pword = new unsigned int [N*N];

unsigned int* * p_pword;    //pointers to permutation words
p_pword = new unsigned int* [N];

//setting up the pointers on the locations such that if N=4 then 0,4,8,12,...
int count;
for(count=0;count<N;count++)
        p_pword[count]=&pword[count*N];

I am not asking for someone to provide me with code, i just want to know is there any way i can setup pointers to single array of data. PS: i have tried the following method but not achieving any speedup at all

int * raw_ptr = thrust::raw_pointer_cast(&d_Data[0]); //doing same with multiple pointers

but i guess due to the fact that i am pointing towards device_vector it might be the problem of slow accessing

Any help in this regard is highly appreciated.

Answer 1

Well this doesn't make any sense:

int * raw_ptr = thrust::raw_pointer_cast([0]);
                                          ^ what is this??

I don't think that line would compile correctly.

But in thrust you can certainly do something like this:

#include <thrust/host_vector.h>
#include <thrust/device_vector.h>
#include <thrust/device_ptr.h>
#include <thrust/sequence.h>

int main(){

  int N=16;
  thrust::device_vector<int> d_A(4*N);
  thrust::sequence(d_A.begin(), d_A.end());
  thrust::device_ptr<int> p_A[N];
  for (int i=0; i<N; i++)
    p_A[i] = &(d_A[4*i]);
  thrust::host_vector<int> h_A(N);
  thrust::copy(p_A[4], p_A[8], h_A.begin());
  for (int i=0; i<N; i++)
    printf("h_A[%d] = %d\n", i, h_A[i]);
  return 0;
}

Not sure what to say about speedup. Speedup in the context of the tiny little snippet of code you've posted doesn't make much sense to me.