[erlang-bugs] Erlang 18.0-rc1 is behaving slower than 17.4 (and 17.5)

[Kenneth Lundin]

In 18 Rc1 the timer wheel size per scheduler is set to 1 Mwords = 8 Mbytes,
this is too high. We plan to lower this to 64K words = 0.5 Mbytes per
scheduler in the next 18 Rc. Note that in OTP 17 there is 1 timer wheel
with size 64K words.

/Kenneth Erlang/OTP Team, Ericsson

On Tue, Apr 14, 2015 at 7:55 AM, José Valim <jose.valim@REDACTED
> wrote:

> This is most likely due to multiple timer wheels in 18. We now have one
>> wheel per scheduler and a larger wheel to boot. I'm unsure to why it is so
>> large though. Rickard? TIW 16x larger?
>>
>> You can see the size vary with +S <n> switch.
>>
>
> Yup, it is the due to the timer wheel. +S 1 reduces it. I believe Lukas
> mentioned it would take around 1 word MB per scheduler.
>
> It is likely this higher memory usage is going to cause confusion for
> folks jumping into Erlang 18.0 if we don't provide proper disclaimers, even
> more for those in the embedded space as I often hear the memory footprint
> to be one of Erlang VM benefits.
>
> Maybe one solution is to ship with smaller wheels but allow the size to be
> configurable?
>
>
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