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Asked: 2026-05-13T09:49:18+00:00

I’m studying Erlang’s process model at the moment. I have hit a snag in

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I’m studying Erlang’s process model at the moment. I have hit a snag in a tech report (section 3, paragraph 2) on Erlang:

This explains why it in some cases can be more efficient to run several SMP VM’s
with one scheduler each instead on one SMP VM with several schedulers. Of course
the running of several VM’s require that the application can run in many parallel tasks
which has no or very little communication with each other.

Now this paragraph is confusing me; I can see the uni-process multiple scheduler scenario, but I am failing to see multiple processes with a single scheduler; Presumably each process would have a different node name, and this would mean a certain application, without modification, cannot be used with this model; the virtue of not requiring modification has been mentioned as a key feature of SMP in the report. If the multiple processes have the same node names, than performance would be disastrous due to inter-Erlang-process messaging storms — this assume the use of in-memory amnesia. Is there some process model that is not introduced in the article and that I am missing here ?

What is the author trying say here ? is he trying to suggest that an application would have to be rewritten (to take multiple unique node-names into account) for the multi-process single-scheduler case ?

— edit 1: Clarification of Source of Problem —

The question has been answered through discussion; the following is an outline of the trouble I had.

The issue for this question has been that the documentation, as I recall, does not touch on a scenario of running multiple Erlang emulators per physical machine — it has always been shown that the emulator represents your physical machine (in industrial usage); also, the scenario of having to explicitly partition a program for computational efficiency has never been considered. This sudden introduction has been the source of my woe.

The convention is still biased towards creating LOTS of processes and that the future holds many improvements for the SMP emulator for Erlang, and this means that single node per machine is still a very viable option assuming favourable application design.

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1 Answer

  1. Editorial Team

    Rewrite after reading article:

    This explains why it in some cases can
    be more efficient to run several SMP
    VM’s with one scheduler each instead
    on one SMP VM with several schedulers.

    • Non-SMP VM has no-lock so runs fast.
    • Single scheduler SMP VM 10% slower, due to cost of checking locks
    • Multiple scheduler SMP VM slower again due to using/waiting for locks

    Of course the running of several VM’s
    require that the application can run
    in many parallel tasks which has no or
    very little communication with each
    other.

    • I think: Nodes on the same server have to have different names.
    • Inter process messaging while by slower due to the inter-process nature verse intra process messaging of a VM node.
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