class_docstr: Single training iteration loop of the model.
  
  Performs: data read, forward, loss computation, backward, optimizer step, parameter updates.
  
  Various intermediate steps are also performed:
  - logging the training loss, training eta, LR, etc to loggers
  - logging to tensorboard,
  - performing any self-supervised method specific operations (like in MoCo approach, the
  momentum encoder is updated), computing the scores in swav
  - checkpointing model if user wants to checkpoint in the middle
  of an epoch
code: def update_meters(task: ClassyTask, model_output, target):
      if len(task.meters) == 0:
          return
  
      with_train_meters = task.config["METERS"]["enable_training_meter"]
      if (task.train and with_train_meters) or (not task.train):
          with PerfTimer("meters_update", task.perf_stats):
              if isinstance(model_output, list):
                  model_output_cpu = [x.cpu() for x in model_output]
              else:
                  model_output_cpu = model_output.cpu()
              for meter in task.meters:
                  meter.update(model_output_cpu, target.detach().cpu())
  
imports: import contextlib
  from types import SimpleNamespace
  from typing import Any, Dict
  import torch
  from classy_vision.generic.distributed_util import all_reduce_mean
  from classy_vision.tasks import ClassyTask
  from classy_vision.tasks.classification_task import AmpType
  from vissl.hooks import SSLClassyHookFunctions
  from vissl.trainer.train_steps import register_train_step
  from vissl.utils.activation_checkpointing import manual_gradient_all_reduce, manual_sync_params
  from vissl.utils.fsdp_utils import is_fsdp_model
  from vissl.utils.misc import is_apex_available, torch_version
  from vissl.utils.perf_stats import PerfTimer
  from vissl.utils.profiler import record_function
label_desc: Use image node_id 7 for calling the StandardTrainStep obj's underlying member method code with example usage: obj.update_meters(task, model_output, target) without return types