2020-03-18-sculpt-affinity.txt

                     CPU affinity with Sculpt OS

With the latest 20.02 Sculpt release we added support to configure the affinity
and number of CPUs available to components running on Sculpt. The principal
support was already part of the Genode framework since
[https://genode.org/documentation/release-notes/13.08#Management_of_CPU_affinities - 13.08 (release notes)],
but missed to be easily usable on previous Sculpt versions.

When using some CPU tool, like [http://www.genodians.org/alex-ab/2019-12-23-top-view - top-view],
one will see that most runtime components will run on the first CPU.

[image affinity0]

In order to change the affinity parameters you may now adjust the affinity
space parameters by adjusting the xpos/ypos and the available
CPUs by width/height in a launcher file or start node of your deploy file.
Please read for more details about the concept the 13.08 release notes and/or
the Genode foundation book.

! /rw/config/20.02/launcher/firefox@seoul
!
! <launcher name="firefox@seoul" xpos="1" ypos="0" width="2" height="1"
!                                version="2" pkg="alex-ab/pkg/firefox@seul/...">
! ...
! </launcher>

! /config/deploy
!
! <start name="top_view" xpos="1" ypos="0" width="1" height="1"
!                        version="2" pkg="alex-ab/pkg/top_view/...">
! ...
! </start>

By adding/changing the version attribute the component gets restarted and placed
immediately.

[image affinity1]

In order to know which affinity values are meaningful, look for an affinity node
in /config/managed/runtime, e.g.:

! <affinity-space width="4" height="1"/>

That means sensible values are for xpos 0-3,
for width 1-4 (depending on xpos), for ypos 0 and height 1.

In the future we may make this affinity configuration step available by some
graphical tooling to ease life.

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