code: def calculate_bwd_time(n: Node) -> float:
      """A helper function to calculate `bwd_time` (with sharding spec)
      Args:
          n (Node): a node from the graph
      Returns:
          bwd_time (float): the result of `bwd_time`
      """
      # TODO(super-dainiu): should divide the time by the number of GPUs as well as TFLOPs
      return n.meta["bwd_time"]
  
file_path: colossalai/colossalai/fx/profiler/shard_utils.py
imports: import torch
  from torch.fx import Node
  from .._compatibility import compatibility, is_compatible_with_meta
  from .memory_utils import activation_size
label_desc: Use image node_id 5 for calling a global function with example usage: calculate_bwd_time(n) and returns: n