Create local array dynamic inside OpenCL kernel

问题

I have a OpenCL kernel that needs to process a array as multiple arrays where each sub-array sum is saved in a local cache array.

For example, imagine the fowling array:

[[1, 2, 3, 4], [10, 30, 1, 23]]

• Each work-group gets a array (in the exemple we have 2 work-groups);

• Each work-item process two array indexes (for example multiply the value index the local_id), where the work-item result is saved in a work-group shared array.

  __kernel void test(__global int **values, __global int *result, const int array_size){
      __local int cache[array_size];
  
      // initialise
      if (get_local_id(0) == 0){
          for (int i = 0; i < array_size; i++)
              cache[i] = 0;
      }
  
      barrier (CLK_LOCAL_MEM_FENCE);
  
      if(get_global_id(0) < 4){
          for (int i = 0; i<2; i++)
              cache[get_local_id(0)] += values[get_group_id(0)][i] * 
                                                           get_local_id(0);
      }
  
      barrier (CLK_LOCAL_MEM_FENCE);
  
      if(get_local_id(0) == 0){
          for (int i = 0; i<array_size; i++)
              result[get_group_id(0)] += cache[i];
      }
  }
  

The problem is that I can not define the cache array size by using a kernel parameter, but i need to in order to have a dynamic kernel.

How can I create it dynamically? like malloc function in c...

Or the only solution available is to send a temp array to my kernel function?

回答1:

This can be achieved by adding __local array as a kernel parameter:

__kernel void test(__global int **values, __global int *result, 
    const int array_size, __local int * cache)

and providing desired size of the kernel parameter:

clSetKernelArg(kernel, 3, array_size*sizeof(int), NULL);

The local memory will be allocated upon the kernel invocation. Note, that extra checks may be necessary to ensure that required local memory size does not exceed the device limit.

来源：https://stackoverflow.com/questions/17574570/create-local-array-dynamic-inside-opencl-kernel