Version 1.1.0 with high %CPU

Hi~ I have found that my process occupies higher CPU(about 400% or higher) with version 1.1.0 than with version 1.0.1 or version 0.4.1(about 100%).
The above phenomenon happens only on setting pip_memory = True in DataLoader. When setting pip_memory = Flase, the CPU is about 100%. Besides, num_workers is 6.
Could you please tell me how to configue my pytorch 1.1.0 to maintain CPU not too high with pip_memory still True ?