title: How to run Flow training on 2 GPU(s)?
body: <p>Repost from Wouter J.</p>
  
  <p>How can I run the flow training on GPU(s)?</p>
  
  <p>I'm currently trying to get the <code>ppo_runner</code> benchmark to work with my 2 GPU's. However, I can't find any way to make use of these resources. 
  What would I need to change in the code to make use of the GPU's?</p>