[erlang-questions] Deprecation and removal of the non-smp emulator

Dmytro Lytovchenko <>
Mon Apr 3 15:50:31 CEST 2017


One point that I've heard a couple of times, is that single CPU emulator
(not sure which one of them) is noticeably (like up to 20%) faster than SMP
due to all the locks it doesn't have to maintain. So for some applications
running say 8 of these will be better than a single SMP 8 core emulator.
This is a casual opinion from the couch and I don't have the numbers to
prove the point :)

2017-04-03 15:33 GMT+02:00 Lukas Larsson <>:

> Hello!
>
> At the moment it is possible to build three different production versions
> of the Erlang VM; the smp emulator, the threaded non-smp emulator and the
> non-threaded non-smp emulator.
>
> The non-smp versions have been kept around since the introduction of the
> smp emulator as they can run on OS:s without thread support and also for
> certain applications they provide a small performance boost. However we now
> feel that they have outlived their usefulness and plan to remove them.
>
> The main reason why we want to remove non-smp is because we do not want to
> spend time on implementing the dirty-scheduler feature for threaded
> non-smp, which is something we would have to do for the threaded non-smp
> emulator to remain production quality. The different variants also increase
> our test-scope by quite a lot, so reducing that is a very beneficial side
> effect.
>
> The current plan is for the non-smp emulators to be deprecated and not
> built by default in OTP-20, and then removed completely in OTP-21.
>
> If you have a very good reason for wanting to use the non-smp emulator,
> please do let us know as soon as possible so that we can consider whether
> we want to keep the non-smp version anyway.
>
> Lukas
>
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