How do get the physical flag for a cl_device_id.

      I have multiple GPUs, and they have the same name, such as "HD 7970". My program has multiple tasks, each task relate to a cl_device_id(for example, 3 GPUs and 6 tasks), at this time, the 6 cl_device_id are different pointer but they may be on the same physical GPU, however, I want to know for a certern task, which GPU I'm using now, Is there any way?

     I thought that I could call clGetDeviceInfo to get the physical id for the gpu, or which pcie slot the gpu plugged in, but I didn't found these properties.