class_docstr: Set GPU affinity and increase the L2 fetch granularity.
  Adapted from https://github.com/NVIDIA/DeepLearningExamples/tree/master/PyTorch/LanguageModeling/Transformer-XL
code: def on_init_start(self, trainer: Trainer) -> None:
      set_affinity(trainer)
  
file_path: zoo/src/callbacks/gpu_affinity.py
imports: import torch
  from pytorch_lightning import Callback, Trainer, LightningModule
  import logging
label_desc: Use image node_id 2 for calling the GpuAffinity obj's underlying member method code with example usage: obj.on_init_start(trainer) without return types