huge fan of elixir. and definitely have some dumb questions.

in some of the realtime architectures i've seen, certain processes get priority, or run at certain Hz. but i've never seen this with the beam. afaik, it "just works" which is great most of the time. i guess you can do: Process.flag(:priority, :high) but i'm not sure if that's good enough?

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toast0 7 days ago | parent [-]

Beam only promises soft realtime. When switching processes, runnable high priority tasks will be chosen before runnable normal or low priority tasks, and within each queue all (runnable) tasks run before a task runs again. But beam isn't really preemptive; a normal or low priority task that is running when a high priority task becomes runable won't be paused; the normal task will continue until it hits its reduction cap or blocks. There's also a chance that maybe you hit some operation that is time consuming and doesn't have yield points; most of ERTS has yield points in time consuming operations, but maybe you find one or maybe you have a misbehaving NIF.

Without real preemption, consistently meeting strict timing requirements probably isn't going to happen. You might possibly run multiple beams and use OS preemption?

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heeton 7 days ago | parent [-]

I spoke with Peer (the creator of Grisp) about this at Elixirconf earlier in the year, and I'm not an expert here so I hope I don't misrepresent his comments:

Grisp puts enough controls on the runtime that soft-realtime becomes hard-realtime for all intents and purposes, outside of problems that also cause errors in hard-realtime systems.

(Also, thanks Peer for being tremendously patient with a new embedded developer! That kind of friendly open chat is a huge draw to the Elixir community)

	▲	cyberpunk 7 days ago \| parent [-]
		I did the same workshop some years ago with him also, very nice and patient guy, I can recommend attending if anyone is curious how microelectronics actually work :}