Profiler is great, do we need anything else?

Came up in context of checking out performance #1830 (closed)

We have our own profiler. Others have experience with OpenTracing, ZipKin or another distributed tracing solution. OpenTracing is open and almost zero-cost when not tracing.

• are we missing any functionality by using our own profiler, and will another tool be a better or just similar choice?
• clarify where the measurement with Profiler starts and ends? Does it run on Azure or a separate network? It measures on GitLab.com directly? Starting at an input into a frontend worker?

@stanhu @andrewn would love to have you figure this one out... since you've developed and worked with various tools