CUDA Global Array declaration and initialization before kernel call example

Question

I need some help with CUDA global memory. In my project I must declare global array for avoid to send this array at every kernel call.

Edit:

My application can call the kernel more than 1,000 times, and on every call I'm sending him an array with size more than [1000 * 1000], So I think it's taking more time , that's why my app works slowly. So I need declare global array for the GPU and my questions are

1. How to declare Global array?

2. How to initialize a global array from CPU before the kernel launch?

Thanks in advance!

Answer 1

Your edited question is confusing because you say you are sending your kernel an array of size 1000 x 1000 but you want to know how to do this using a global array. The only way I know of to send this much data to a kernel is to use a global array, so you are probably already doing this with an array in global memory.

Nevertheless, there are 2 methods, at least, to create and initialize an array in global memory:

1.statically, using __device__ and cudaMemcpyToSymbol, for example:

 #define SIZE 100
 __device__ int A[SIZE];
 ...
 int main(){
   int myA[SIZE];
   for (int i=0; i< SIZE; i++) myA[i] = 5;
   cudaMemcpyToSymbol(A, myA, SIZE*sizeof(int));
   ...
   (kernel calls, etc.)
 }

(device variable reference, cudaMemcpyToSymbol reference)

2.dynamically, using cudaMalloc and cudaMemcpy:

 #define SIZE 100
 ...
 int main(){
   int myA[SIZE];
   int *A;
   for (int i=0; i< SIZE; i++) myA[i] = 5;
   cudaMalloc((void **)&A, SIZE*sizeof(int));
   cudaMemcpy(A, myA, SIZE*sizeof(int), cudaMemcpyHostToDevice);
   ...
   (kernel calls, etc.)
 }

(cudaMalloc reference, cudaMemcpy reference)

For clarity I'm omitting error checking which you should do on all cuda calls and kernel calls.