If you’re trying to benchmark libraries you’ll have much better and more useful results with a benchmarking library like benchee.

In any VM environment benchmarking is very tricky, you never know if you are benchmarking your actual code or the implementation of the VM. You really need to do many invocations and do a statistical analysis. Using :tc.timer in iex can provide very misleading results.env MIX_ENV=prod also effects the timing results.

Benchee , Benchfella and other similar libraries help, but even with those there are some gotchas. If you are simply looking for order of magnitude results, then :tc.timer in iex is probably ok, but I would not trust it beyond that.

I may be wrong, but I think iex is entirely interpreted.
Do note, that means that defmodule'ing inside iex will interpret the defmodule call, but that really does compile a module and code run ‘inside’ those functions are fast.