about INT8 mode Arguments

-C CACHE_FILE: Path to calibration cache file,only used in int8 mode.The default value is ./cal.bin.
What does this parameter mean and how does the calibration file be generated?

[TensorRT] INFO: Calculating Maxima
[TensorRT] INFO: Calibrating with batch 0
[TensorRT] INFO: Calibrating with batch 1
[TensorRT] INFO: Calibrating with batch 2
[TensorRT] INFO: Calibrating with batch 3
[TensorRT] INFO: Calibrating with batch 4
[TensorRT] INFO: Calibrating with batch 5
[TensorRT] INFO: Calibrating with batch 6
[TensorRT] INFO: Calibrating with batch 7
[TensorRT] INFO: Calibrating with batch 8
[TensorRT] INFO: Calibrating with batch 9
[TensorRT] ERROR: Tensor activation_55/Relu is uniformly zero; network calibration failed.
python: …/builder/cudnnBuilder2.cpp:1227: nvinfer1::cudnn::Engine* nvinfer1::builder::buildEngine(nvinfer1::CudaEngineBuildConfig&, const nvinfer1::cudnn::HardwareContext&, const nvinfer1::Network&): Assertion `it != tensorScales.end()’ failed.