CODEWITHSUNDEEP
c++opencl
CAPS LOCK
CAPS LOCK

Reputation: 2040

How to pass array in kernel, do something and then return it - OpenCL

I am trying to pass an array to OpenCL kernel, then do something with it and pass it back to host. I have modified code in this tutorial.

This is just kernel for figuring out how OpenCL actually works. I hope that this would just substract 2 from the first element of array1 and store it into the first element of array2: 

__kernel void test(global int* array1, global int* array2) {
    array2[0] = array1[0] - 2;
}

In main I have two arrays, one (host1) with some numbers and the second (host2) initialized to zeros. Than to create memory buffers I use:

memobj = clCreateBuffer(context, CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR, MEM_SIZE * sizeof(int), &host1, &ret);
memobj2 = clCreateBuffer(context, CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR, MEM_SIZE * sizeof(int), &host2, &ret);

After building program I set arguments:

ret = clSetKernelArg(kernel, 0, sizeof(cl_mem), &host1);
ret = clSetKernelArg(kernel, 1, sizeof(cl_mem), &host2);

And then after execution I try to get that array back.

ret = clEnqueueReadBuffer(command_queue, memobj2, CL_TRUE, 0, MEM_SIZE * sizeof(int), host2, 0, NULL, NULL);

Here if I change memobj2 to memobj the host2 will contain values of host1, otherwise it stays the same. I guess that this is not how one will return arrays.

I am stuck at this point.

Upvotes: 4

Views: 3106

Answers (1)

jprice
jprice

Reputation: 9925

Your calls to clSetKernelArg() are invalid - you should be passing the OpenCL buffer, not the host pointer. For example:

ret = clSetKernelArg(kernel, 0, sizeof(cl_mem), &memobj);
ret = clSetKernelArg(kernel, 1, sizeof(cl_mem), &memobj2);

As was already pointed out, you should check the return codes from every OpenCL runtime API call. This would point you towards the error pretty quickly.

Upvotes: 6

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