CUDA: Memory allocation for pointer to pointer using cudaMallocHost(...);

Question

I changed my method to allocate host memory from method 1 to method 2 as shown in my code below. The code can compile and run without any error. I just wonder is it a proper way or any side effect to allocate memory for pointer to pointer using method 2.

#define TESTSIZE  10
#define DIGITSIZE 5

//Method 1  
int **ra;
ra = (int**)malloc(TESTSIZE * sizeof(int));
for(int i = 0; i < TESTSIZE; i++){
    ra[i] = (int *)malloc(DIGITSIZE * sizeof(int));
}

//Method 2  
int **ra;
cudaMallocHost((void**)&ra, TESTSIZE * sizeof(int));

for(int i = 0; i < TESTSIZE; i++){
    cudaMallocHost((void**)&ra[i], DIGITSIZE * sizeof(int));
}

score 2 · Answer 1 · edited Feb 22 '16 at 20:34

Both of them work fine. Yet, there are differences between cudaMallocHost and malloc. The reasons is that cudaMallocHost allocates pinned memory so under the hood the OS's doing something similar to malloc and some extra functions to pin the pages. This means that cudaMallocHost generally takes longer.

That being said, if you repeatedly want to cudaMemcpy from a single buffer then cudaMallocHost may benefit in the long run since it's quicker to transfer data from pinned memory.

Also, you are required to use pinned memory to overlap data transfer/computations with streams.

CUDA: Memory allocation for pointer to pointer using cudaMallocHost(...);

1 Answers1