Update real-time capability check for multimacd

[honsma235]

Description

Use more generic way to test if we can change real-time scheduling attributes.

On a kernel compiled with CONFIG_RT_GROUP_SCHED=y each cgroup domain which wants to use real-time scheduling would need to allocate rt_runtime_us.

If you are stuck with such a kernel one can disable the limit altogether changing the kernel parameter with sudo sysctl -w kernel.sched_rt_runtime_us=-1 or
echo "kernel.sched_rt_runtime_us = -1" | sudo tee /etc/sysctl.d/10-disable-rt-group-limit.conf to make it permanent.

The previous check for real-time capability fails in this case, because it only checks for rt_runtime_us > 0 in the cgroup settings which don't reflect the kernel parameter.

Related Issue

home-assistant/operating-system#1235
home-assistant/operating-system#2168
#1191

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Alternate Designs

None considered

Possible Drawbacks

Not that I'm aware of

Verification Process

Implemented and tested locally on a Radxa 4SE with Debian Bullseye and Home Assistant supervised install

Release Notes

N/A

Contributing checklist

• My code follows the code style of this project.
• I have read the CONTRIBUTING and LICENSE document.
• I fully agree to distribute my changes under Apache 2.0 license.

[jens-maus]

Thx for your contribution. I do have two small comments/requests before accepting this PR:

1. Please check and elaborate that the chrt commands are available for all supported RaspberryMatic platforms.
2. You changed the final ERROR output and do not provide some additional technical hint in how exactly a user could fix that issue or how the error could be interpreted correctly or actually googled. So please rephrase that final ERROR in case the cgroups feature/setting is missing so that user get some more technical hints what could actually be the reason or potential solution.

[jens-maus]

Please adapt as requested

[honsma235]

As for the availability of chrt:
It is part of Busybox and enabled in Busybox.config

RaspberryMatic/buildroot-external/Busybox.config

Line 611 in c6a4faa

CONFIG_CHRT=y

so I guess it should be available in all builds.

But not sure where the file comes from. The header says something about automatically generated.