Real time scheduling

[jgauthier]

I'm hesitant to post this here, because I am not really sure that this is an armbian issue to begin with.  But I'm somewhat stumped.

During the build process I configured the kernel to enable real time threads.

 

CONFIG_NO_HZ_COMMON=y
CONFIG_HZ_1000=y
CONFIG_HZ=1000
CONFIG_PREEMPT_RT=y

 

However, as I started to migrate my development I discovered I couldn't create a real time thread.

So I pulled down areal time test suite (https://wiki.linuxfoundation.org/realtime/documentation/howto/tools/rt-tests)

And confirmed it has the same issue:

 

Unable to change scheduling policy!
either run as root or join realtime group

 

I am root, it is a real time kernel.

Linux bananapim4zero 6.13.7-edge-sunxi64 #1 SMP PREEMPT_RT Thu Mar 13 12:08:08 UTC 2025 aarch64 GNU/Linux

 

I am not sure what might be driving this.  For the past several months I've been doing some dev work on a TI AM625 based board that I built a yocto distribution on and it's fine.

I know that is a completely different board, but my kernel setting for real time enablement are the same.  I pulled them from that build since.

 

Appreciate any input!

[Werner]

8 hours ago, jgauthier said:

completely different board,

Exactly. Kernel support for this board might not be good enough (yet) or even might work just fine but if the hw doesn't cut it, it might be just a big waste of time.

[jgauthier]

I think my issue is actually that CONFIG_RT_GROUP_SCHED is enabled.

 

I was certain I had disabled it.  After some sluething.. It turns out I don't know how to configure/build a kernel.  

 

I run

./compile.sh BOARD=bananapim4zero BRANCH=edge kernel-config

 

I then make some changes and tell it to save:

 

For instance when I enter menuconfig, I see this.

 

I then REMOVE the check.

 

 

I say YES

 

 

OOPS. I realized I wanted to make another change.

 

 

And now it's back. 

 

After unchecking this, and building the kernel, moving the kernel, installing, and rebooting I see the config hasn't change on board.

So, I must have a misunderstanding of how this is supposed to work.

 

I checked here: https://docs.armbian.com/Developer-Guide_Build-Commands/

Which says "Add or Remove" modules, but doesn't elaborate if it's copying some defaults or where they might be coming from.

 

 

 

 

 

[going]

19 часов назад, jgauthier сказал:

And now it's back. 

 

After unchecking this, and building the kernel, moving the kernel, installing, and rebooting I see the config hasn't change on board.

So, I must have a misunderstanding of how this is supposed to work.

 

I checked here: https://docs.armbian.com/Developer-Guide_Build-Commands/

Which says "Add or Remove" modules, but doesn't elaborate if it's copying some defaults or where they might be coming from.

 

19 часов назад, jgauthier сказал:

I run

./compile.sh BOARD=bananapim4zero BRANCH=edge kernel-config

After you complete the configuration of the kernel, the build system will tell you where and under what name it has saved your configuration file.

 

Next, you need to save it with a name

config/kernel/linux-sunxi64-edge.config

and commit it to the build system itself.

 

or save it under the name

userpatches/config/kernel/linux-sunxi64-edge.config

 

Only after that, run

./compile.sh BOARD=bananapim4zero BRANCH=edge kernel

 

[going]

12.04.2025 в 00:43, jgauthier сказал:

CONFIG_NO_HZ_COMMON=y
CONFIG_HZ_1000=y
CONFIG_HZ=1000
CONFIG_PREEMPT_RT=y

As a rule, you also need to set the processor frequency to the maximum value and make it unchanged and configure the Linux kernel scheduler.

[jgauthier]

@going

 

Thanks for your process. I followed it, and using userpatches makes sense.  However, upon installing the new kernel my config changes are still not present.  So I reviewed the kernel build log and I see why:

 

--> (12) COMMAND: ./scripts/config --enable RT_GROUP_SCHED

Which happens are my userpatch file is copied over.

 

I wonder if I have control over this process?

Edited 4 hours ago by jgauthier