I’m running almost those exact options, I have --disable-hipe instead of enable since it’s a dead project.
So here’s something that’s interesting. I did rm -rf _build and then iex -S mix run --no-start --no-compile so that I could open :observer, and then I called the Mix.Task.run("deps.compile") to look at how it performed from Erlang’s perspective.
Here’s what I saw:
Initial:
More deps:
More deps:
This looks super strange to me. Scheduler utilization across the board is super low. I ran compile after the deps were compiled and although it did look like all 10 schedulers got involved (as we see here with some deps) none of them ever exceeded 30%.
I’m not entirely sure what to make of this. The big memory spike was Poison (yes, I know) and I think that’s likely just code gen. Anyone got any insights?
UPDATE:
Running this code trivially uses all 10 schedulers and maxes out cores from an OS level:
iex(3)> defmodule Busy do
...(3)> def loop(x) do
...(3)> loop(x + 1)
...(3)> end
...(3)> end
iex(4)> 1..20 |> Enum.map(fn _ -> spawn(fn -> Busy.loop(0) end)
So maybe the OS is right. Compilation (for some reason) is generally not generating very much scheduler activity (for some reason) and so it can run everything on the efficiency cores. When the schedulers are under load it does seem to happily move them to the performance cores.
