device select on MacBookPro

Hello! Please be a little forgiving, I’m learning C and OpenCL at the same time :wink:
I’m busy querying devices on my mbp to make a choice which gpu to use. I have set up a list of devices with

cl_device_id allCLdevices[4] ;
cl_device_id *selectedCLdevice = &allCLdevices[0];


err = clGetDeviceIDs(NULL, CL_DEVICE_TYPE_GPU, 2, allCLdevices, &numberOfCLdevices);

when I’m getting info about the devices with

for (int devNr=0; devNr<numberOfCLdevices; devNr++) {
     selectedCLdevice = &allCLdevices[devNr]; 
     err = clGetDeviceInfo(*selectedCLdevice, CL_DEVICE_NAME, sizeof(device_name), device_name, NULL);
     printf("device %d: 				%s
", devNr, device_name);

all present GPUs are listed (two of them). Now I’m running the whole (test-)calculation on the CPU, which works fine.
After that I’m running the same CL-routine on the gpu, where I’m trying to select a device with

if (numberOfCLdevices > 1) {
			selectedCLdevice = &allCLdevices[1];
			printf("%s, (%d devices)
", device, numberOfCLdevices);
		}else {
			selectedCLdevice = &allCLdevices[0];

To select the “bigger” GPU on the MacBookPro, which is not being used for display, I’m choosing the selectedCLdevice = &allCLdevices[1], whenever there is more than one device.


selectedCLdevice = &allCLdevices[0] will work (also in the GPU-run), selectedCLdevice = &allCLdevices[1] will give me a nice litte

creating queue... 		queue error number -2

coming from

commandQueue = clCreateCommandQueue(CLcontext, *selectedCLdevice , 0,  &err);

Shouldn’t the secondary gpu, that I’m not using for display, be available for OpenCL just like the first one? Or did I make a mistake with the pointers or the allCLdevices-list?

That is really a question for Apple. Maybe Affie will see your post and comment.

The specific model of the MacBookPro and the energy settings selected by the user (e.g. to conserve battery) effect device availability. These factors may also effect the order of devices in the list returned by clGetDeviceIDs. Your program can check to see if a device is available before attempting to create a command queue on it with the CL_DEVICE_AVAILABLE enum of clGetDeviceInfo.

Good to find out about the the settings (energy). Why would it effect the order of the devices, though. That doesn’t make sense to me.