使用分布式架构训练好模型了，用单个GPU读取测试的时候出现了这个错误：Cannot assign a device for operation 'save/RestoreV2_1': Operation was explicitly assigned to /job:ps/task:0/device:CPU:0 but available devices are [ /job:localhost/replica:0/task:0/device:CPU:0, /job:localhost/replica:0/task:0/device:GPU:0 ]. Make sure the device specification refers to a valid device.
