The built-in profiling modules only provide information about the main thread (at least when invoked as documented). 

To avoid user confusion we should state this in the documentation at https://docs.python.org/3/library/profile.html. 

Potentially we could also suggest mitigations such as manually creating a Profile instance in the user's thread code, but the most important thing is to make clear what the module does/does not do out of the box. 

(see also https://bugs.python.org/issue9609 which discusses a possible non-doc change to help with multi-threading, but looks like that's stalled, so best to push ahead with doc'ng this.