code: def step_model(
      model: nn.Module, input: torch.Tensor, target: torch.Tensor
  ) -> None:
      model.train()
      output = model(input)
      loss = F.mse_loss(output, target.to(output.device))
      loss.backward()
  
imports: import copy
  import os
  import tempfile
  from typing import Any, Dict, List, Tuple, Type
  import unittest
  import pytest
  import torch
  from torch import nn
  import torch.distributed
  import torch.nn.functional
  import fairscale.experimental.nn.data_parallel.gossip
  from fairscale.fair_dev.testing.testing import skip_if_single_gpu, spawn_for_all_world_sizes
label_desc: Use image node_id 2 for calling a global function with example usage: step_model(model, input, target) without return types