Here's a demonstration of how IO/CPU interact with the GVL to affect the throughput of your Puma or Sidekiq application. Give it a run (gem install parallel first) and see what happens! You can also try removing the GVL by making Parallel use processes instead of threads.

https://gist.github.com/nateberkopec/b57599281cab58f08e506514eb7b2e49