Not able to use openCL on Mac

Question

I am trying openCV+Yolo3. I am using Mac with this config:

• MacBook Pro (Retina, 15-inch, Mid - 2015)
• Graphics Intel Iris Pro 1536 MB

Update - OS info:

• macOS Catalina version 10.15.2

I checked Apple website and it says this MacBook supports openCL 1.2: https://support.apple.com/en-ca/HT202823

My program uses opencv-contrib-python 4.1.2. And the code snippet is:

net = cv2.dnn.readNetFromDarknet(model_configuration, model_weights) 
net.setPreferableBackend(cv2.dnn.DNN_BACKEND_OPENCV) 
net.setPreferableTarget(cv2.dnn.DNN_TARGET_OPENCL)

I also tried DNN_TARGET_OPENCL_FP16. BTW, I use the common pre-trained yolo3 cfg and weights and coco.names.

The problem is, my program cannot use GPU on my Mac. When I run a video through it, the inference time is 300+ ms per frame and from Activity Monitor I can see that the GPU usage is 0.0% while CPU is 70%+. I don't know why I can't use GPU via openGL on the Mac. Is there any trick I miss?

• C.Nivs: From this question it looks like you can set the device settings to use the GPU explicitly device = platform.get_devices()[1]; ctx = cl.Context([device]) # Tell CL to use GPU
• Z.Wei: Thanks. I read through it but it seems it is a different problem. In openCV do we have similar APIs or we can config these when building openCV? @C.Nivs
• C.Nivs: Sorry, misread that question