问TensorflowLite推理时间为0？

EN

import os
import time
import cv2
import numpy as np
import tensorflow as tf


def load_model(model_path):
    return (tf.lite.Interpreter(model_path=model_path))

def init_tflite(interpreter):
    interpreter.allocate_tensors()

    
def predict_tflite(interpreter, x_test_):
    input_details = interpreter.get_input_details()[0]
    output_details = interpreter.get_output_details()[0]
    # If required, quantize the input layer (from float to integer)
    input_scale, input_zero_point = input_details["quantization"]
    if (input_scale, input_zero_point) != (0.0, 0):
        x_test_ = x_test_ / input_scale + input_zero_point
        x_test_ = x_test_.astype(input_details["dtype"])
        
    # Invoke the interpreter
    interpreter.set_tensor(input_details["index"], [x_test_[0]])
    
    t1 = time.time_ns()
    interpreter.invoke()
    t2 = time.time_ns()
    y_pred = interpreter.get_tensor(output_details["index"])[0]
        
    # If required, dequantized the output layer (from integer to float)
    output_scale, output_zero_point = output_details["quantization"]
    if (output_scale, output_zero_point) != (0.0, 0):
        y_pred = y_pred.astype(np.float32)
        y_pred = (y_pred - output_zero_point) * output_scale

    return y_pred, t2-t1

def inference_model(frame, model):
    nframe = cv2.resize(frame, (32,32))
    nframe = np.expand_dims(nframe, axis=2)
    image = np.expand_dims(nframe, axis=0)
    image  = np.array(image, dtype=np.float32)
    pred, diff = predict_tflite(model, image)
    print("Inference Time {a} ns".format(a=diff))
    return np.argmax(pred) == 0


im = np.ones((700,100))
im = np.array(im, dtype=np.float32)
model = load_model('models/tflite_model_f16_no_opt.tflite')
init_tflite(model)
for i in range(0, 10):
    pred = inference_model(im, model)

PS C:\repos\image-based-cell-sorting\ibcs\cellsorter> python .\tflite_test.py
2022-09-28 14:30:34.605393: W tensorflow/stream_executor/platform/default/dso_loader.cc:64] Could not load dynamic library 'cudart64_110.dll'; dlerror: cudart64_110.dll not found
2022-09-28 14:30:34.605835: I tensorflow/stream_executor/cuda/cudart_stub.cc:29] Ignore above cudart dlerror if you do not have a GPU set up on your machine.
INFO: Created TensorFlow Lite XNNPACK delegate for CPU.
Inference Time 0 ns
Inference Time 0 ns
Inference Time 0 ns
Inference Time 0 ns
Inference Time 0 ns
Inference Time 0 ns
Inference Time 0 ns
Inference Time 447900 ns
Inference Time 0 ns
Inference Time 0 ns