CODEWITHSUNDEEP
concurrencyparallel-processingopencl
MPKenning
MPKenning

Reputation: 569

Supplying a pointer renders my OpenCL code incorrect

My computer has a GeForce 1080Ti. With 11GB of VRAM, I don't expect a memory issue, so I'm at a loss to explain why the following breaks my code.

I execute the kernel on the host with this code.

cl_mem buffer = clCreateBuffer(context.GetContext(), CL_MEM_READ_WRITE, n * n * sizeof(int), NULL, &error);
error = clSetKernelArg(context.GetKernel(myKernel), 1, n * n, m1);

error = clSetKernelArg(context.GetKernel(myKernel), 0, sizeof(cl_mem), &buffer);

error = clEnqueueNDRangeKernel(context.GetCommandQueue(0), context.GetKernel(myKernel), 1, NULL, 10, 10, 0, NULL, NULL);

clFinish(context.GetCommandQueue(0));

error = clEnqueueReadBuffer(context.GetCommandQueue(0), buffer, true, 0, n * n * sizeof(int), results, 0, NULL, NULL);

results is a pointer to an n-by-n int array. m1 is a pointer to an n-by-n-bit array. The variable n is divisible by 8, so we can interpret the array as a char array.

The first ten values of the array are set to 1025 by the kernel (the value isn't important):

__kernel void PopCountProduct  (__global int *results)
{
    results[get_global_id(0)] = 1025;
}

When I print out the result on the host, the first 10 indices are 1025. All is well and good.

Suddenly it stops working when I introduce an additional argument:

__kernel void PopCountProduct  (__global int *results, __global char *m)
{
    results[get_global_id(0)] = 1025;
}

Why is this happening? Am I missing something crucial about OpenCL?

Upvotes: 0

Views: 54

Answers (1)

Timur Magomedov
Timur Magomedov

Reputation: 74

You can't pas host pointer to clSetKernelArg in OpenCL 1.2. Similar thing can only be done in OpenCL 2.0+ by clSetKernelArgSVMPointer with SVM pointer if supported. But most probable making a buffer object on GPU and copying host memory to it is what you need.

Upvotes: 1

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