CODEWITHSUNDEEP
opencl
itzjackyscode
itzjackyscode

Reputation: 1104

OpenCL: How do I copy a GPU array to the CPU?

I'm porting some CUDA code to OpenCL. The CUDA code does something like this:

// GPU code...
__device__ int counter;

// CPU code...
int data;
cudaMemcpyFromSymbol(gpuData, &data, sizeof(int), 0, cudaMemcpyDeviceToHost);

What would be the equivalent in OpenCL? Similarly, how would I do this for an array? The only way I know involves allocating an extra buffer, copying to it on the GPU, then reading from it on the CPU.

Upvotes: 0

Views: 230

Answers (1)

ProjectPhysX
ProjectPhysX

Reputation: 5764

Use the clEnqueueReadBuffer command, or with the C++ bindings:

T* host_buffer = nullptr; // host buffer
cl::Buffer device_buffer; // device buffer
cl::CommandQueue cl_queue; // command queue

cl_queue.enqueueReadBuffer(device_buffer, blocking, offset*sizeof(T), length*sizeof(T), (void*)(host_buffer+offset));

For a quick overview of OpenCL API calls, see the OpenCL Reference Card. If you want to make using OpenCL in C++ way easier and less bloated, see this OpenCL-Wrapper.

Upvotes: 1

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