# Erl Schedulers - how to use/combine +S ,+sbt, +sct?

**URL:** <https://erlangforums.com/t/erl-schedulers-how-to-use-combine-s-sbt-sct/2543>\
**Category:** Questions / Help\
**Tags:** erlang\
**Created:** [April 17, 2023, 7:25am UTC](https://erlangforums.com/t/erl-schedulers-how-to-use-combine-s-sbt-sct/2543 "2023-04-17T07:25:14Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![dominic](https://erlangforums.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@dominic](https://erlangforums.com/u/dominic)\
**Post date:** [April 17, 2023, 7:25am UTC](https://erlangforums.com/t/erl-schedulers-how-to-use-combine-s-sbt-sct/2543/1 "2023-04-17T07:25:14Z")

</div>

# about `+S Schedulers:SchedulerOnline`

If I set `+S 4:4` for 4 erlang node and open 4 node, it will create 4 system process and 4 thread in every process?

when I want to scale some node just modify online num by [erlang:system\_flag(schedulers\_online, SchedulersOnline)](https://www.erlang.org/doc/man/erlang.html#system_flag_schedulers_online).?

If I can say that `schedulers_online` reduce thread in logical cores to improve system efficiency

# about +sbt & +sct

Is an mapping like this:  
`+sbt` hardware threads =\> `+sct` \<ThreadIds\>  
`+sbt` physical processor chips =\> `+sct` \<ProcessorIds\>

[erlang:system\_info(cpu\_topology)](https://www.erlang.org/doc/man/erlang.html#system_info_cpu_topology). seem not print ‘everything’ normally, so if this is an ordered list of level: `<LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>`

when I set `+sbt L0-3c0-3p0N0`, if `+sbt` will have no effect

the doc have a sample:

```erlang
% erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one
% erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two

```

I’m confusion about how to put these flag together