@classmethod
def label(cls, key, inp):
    """
        Inserts node after `inp` node which will execute eagerly and
        call profiler `label_tracking_start` function. That tells `Profiler`
        to start tracking system statistics and collect them under `key` label.
        """
    if not cls.enabled():
        return inp
    cls._init()
    tf = cls.tf
    x = tf.stop_gradient(tf.py_function(func=cls._profiler_node(cls.
        PROFILER_NODE_START, key), inp=[inp], Tout=inp.dtype))
    x.set_shape(inp.get_shape())
    return x
