Installing linux-image-rt-arm64 from repositories

[rodw]

I know I'm trying to be lazy but why can't we install the PREEMPT_RT kernel from the Debian Bookworm Repositories?

eg with: sudo apt install linux-image-rt-arm64.

This appears to work but it does not boot into the new RT kernel.

 

Downloaded the deb file and used sudo dpkg-i  and it also failed to boot yet this command works if we install a RT kernel we built in the build environment

 

Ran armbian-config and tried to install the kernel but alas its not displayed in the list. Why not?

 

I can pull down Debian Bookworm for the Raspberry Pi from the Debian site and install preempt_rt this way.

Why does Armbian make it so hard?

 

Is there away to select the kernel to boot like we can do  in grub on X86 PC's after installing it with apt?

I know there is a high probability it might crash but at least I'd like to see that with my own eyes.

 

It would be nice if we could install a real time kernel the same way we can do on other platforms.

 

Help and ideas appreciated.

 

Edited June 5, 2023 by rodw

[Werner]

3 hours ago, rodw said:

I know I'm trying to be lazy but why can't we install the PREEMPT_RT kernel from the Debian Bookworm Repositories?

Because generic kernels only work on boards with UEFI or any other standardized interface which most cheap SBCs don't provide. Check https://docs.armbian.com/User-Guide_FAQ/#why-i-cannot-simply-shove-a-random-image-into-my-board-to-work-like-on-my-pc

 

Kernel packages provided by Armbian are individual for each and every board. This is why ours work and generic not.

 

3 hours ago, rodw said:

Downloaded the deb file and used sudo dpkg-i  and it also failed to boot yet this command works if we install a RT kernel we built in the build environment

Reason stated above.

 

3 hours ago, rodw said:

Ran armbian-config and tried to install the kernel but alas its not displayed in the list. Why not?

armbian-config only shows kernels from us since in 99.9% of cases generic kernel won't work. Reason stated above.

 

3 hours ago, rodw said:

Why does Armbian make it so hard?

Get some expensive hardware with proper UEFI support and all generic stuff will work.

 

3 hours ago, rodw said:

I can pull down Debian Bookworm for the Raspberry Pi from the Debian site and install preempt_rt this way.

RPi has just a few boards and thousands of developers and big companies with sponsoring behind that can make something like this possible. Armbian has hundreds of boards but only a few developers and non of that additional stuff. We simply cannot afford to provide packages for each and every corner case and have to limit ourselves to a system that works in most common cases.

 

 

3 hours ago, rodw said:

Is there away to select the kernel to boot like we can do  in grub on X86 PC's after installing it with apt?

There are plans to implement the option to install multiple kernels and to choose which one to boot. No ETA on that though.

 

3 hours ago, rodw said:

It would be nice if we could install a real time kernel the same way we can do on other platforms.

Sure it would. But compared to x86 ARM is still behind in terms of global development power. But it is catching up

 

[Igor]

Just to add a though. We would like to provide rt kernels but this is from current situation everything but simple. Check https://github.com/armbian/build/pull/5166

[wyup]

On 6/5/2023 at 1:59 PM, rodw said:

I can pull down Debian Bookworm for the Raspberry Pi from the Debian site and install preempt_rt this way.

Why does Armbian make it so hard?

How do you do it on Raspi OS? I'm interested.

[mitu]

19 hours ago, wyup said:

How do you do it on Raspi OS? I'm interested.

Almost the same as with Armbian - you get the RT kernel patch and apply it to the kernel you build (if it applies at all). At some point, the RP kernel repo had a RT branch [1], maintained by a 3rd party developer, but hasn't been updated for quite some time. AFAIK the default Raspi OS supplied kernel doesn't have any RT patches added, but you can ask in the RPI forums.

 

[1]https://github.com/raspberrypi/linux/tree/rpi-4.14.y-rt

[rodw]

Sorry guys, I did not get notifications on this thread. Thanks for all the responses.

Back to my quote here:

On 6/5/2023 at 9:59 PM, rodw said:

I can pull down Debian Bookworm for the Raspberry Pi from the Debian site and install preempt_rt this way.

Why does Armbian make it so hard?

 

There is a simple method to get preempt_rt on a raspberry pi running Debian which I have documented in the Linuxcnc docs here

http://linuxcnc.org/docs/2.9/html/getting-started/getting-linuxcnc.html#_install_debian_bookworm_on_a_raspberry_pi

No code or patches required!

I have not tried it against the standard Pi image but I think it would still work as the Pi now uses Debian under the hood.

 

In any case, the Pi's chroot build environment does let you patch the kernel quite simply. Armbian's looked like it should allow that too but it failed for me after applying the preempt-rt patches

I have done it in other ways with help from one of your guys, bit there was a regression that affected latency,

 

If there was a simple way to do the same on Armbian I would have included it in those docs to spread the word. 

Note my post here was driven from a certain amount of frustration while I was writing the docs I linked to.

 

Anyway, we'll get over the line eventually...