Use OpenCL CPU Backend for custom kernel (Opencv 3.2)

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Hi, I want to choose a CPU backend for a custom opencl kernel. I tried context.create(cv::ocl::Device::TYPE_CPU), this tells me it uses the Intel CPU (context.device(0) is the Intel CPU), but the performance is completely identical to the performance using the GPU backend and the CPU usage is at 0-1%. Is there a way to force using the CPU backend? (I want to compare performance)

Thanks in advance,

Peter