[erlang-questions] VM using only 2 out of 8 schedulers available

Kenneth Lundin kenneth.lundin@REDACTED
Thu Feb 16 08:01:14 CET 2012

What is your real problem except that there is no reported cpu load on some
of the cores?

When there is low load on the system i.e. when there are too few runnable
Erlang processes some of the schedulers will automatically be put as idle
letting the remaining schedulers run all processes. When the load increases
the idle schedulers will be taken into service again.

Each scheduler normally runs on one processor core.

Can this explain what you have observed?

/Kenneth Erlang/OTP Ericsson
Den 15 feb 2012 17:53 skrev "Knut Nesheim" <knutin@REDACTED>:

> Dear list,
> From time to time we see the VM using only some of the available
> cores. Typically 2 or 4 out of 8 available cores will be busy, while
> the others are not used at all. From 'top' and 'htop' we see only some
> cores being used.
> We are running the halfword emulator on 8 core machines and the VM is
> correctly reporting the number of schedulers and the underlying
> topology. The nodes are utilizing roughly 25% of each of the 8 cores
> during normal operation.
> This problem appeared again today and we still have the process
> running if anyone has any ideas for how to debug the issue.
> We are on Ubuntu 10.04 LTS, 2.6.32-342-ec2, 64bit, R14B04 with the
> halfword emulator. The only NIF library we are using is jiffy.
> Regards
> Knut
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