That might be, but without me touching anything, I am getting 8 on i7-4870HQ which has 4 physical and 8 virtual cores:
iex(19)> System.schedulers_online
8
iex(20)> System.schedulers
8
dimitarvp
tristan
Rebar3 Core Team
Hauleth probably meant “virtual” in the sense of like cgroup cpu limits and not how cpu cores can have multiple threads?
1
dimitarvp
NobbZ
In CI (especially CI as a service) you often don’t get a VM you run in, but containers. Those see the “real” number of CPUs/cores, while they might be limited in using only 1 or 2 CPUs via cgroup settings.
If though you run your tests in a virtualized rather than a containerized environment, this distinction shouldn’t matter mcuh for you.
1
tristan
Rebar3 Core Team
It could. If your build is run in a container with cpu limits of 1 but the host has 32 then Erlang is going to still bring up 32 schedulers which will likely slow down compilation and anything else being done.
0
dimitarvp
I wonder if that actually happens in all proprietary CI services then. Or do they take special care to pass the proper scheduler count on startup? Would be really useful to know but none of the creators of such services are around AFAIK.
0
tristan
Rebar3 Core Team
It’ll depend on if the service runs your job in a VM or a container.
I’m not sure what you mean by “they take special care”, are there CI services that have special elixir support beyond like cirrus and github actions which just provide configs that run “mix test”?
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dimitarvp
No idea myself. What I had in mind is that I wonder if they pass BEAM startup options that modify the scheduler count. I’d really like to know that.
0