ODroid as raplacement for Raspberry Pi

I got mine working today with the Armbian Debian Bullseye Minimal image and a freshly built 5.19 preempt-rt kernel.

Initial latency numbers are bad. I'm getting at least 75us with 7 glxgears running, while I got 25 - 35 with the Raspberry Pi 4. Needless to say this is very surprising.

The X server appears to be much busier on the N2+ than on the Raspberry Pi 4, even with GPU acceleration enabled. I'm going to start digging there.

great!
So you built the patched kernel from the source at kernel.org?
I got a bit distracted and tried the imges here.
sd-card-images.johang.se/boards/odroid_n2.html
only Bookworm and sid work ...   kinda.

There is a bug which breaks network becasue of an invalid nameserver in resolv.conf
The network comes up but you can't use apt install
This is an issue becasue they sure are minimal images!
no ping and no text editor make it impossible for me to press on with them.
Not to mention bricking my host PC I was working on...

So If I can edit the files on the emmc card. I was going to try adding a nameserver in /etc/network/interfaces for the specific network interface
Currently running a 128 gb emmc on my n2+ with another 64 gb  emmc in the onboard SD I am writing the image to.

But your approach sounds like its pretty good.

With your latency, thats fine for a mesa card. Try isolcpus=2,3 in grub
This isolates cores 2 & 3 so they are only available for RT threads and not accessible from userspace
This may need some experimenting with as the N2 has 6 cores but 2 of them are low power little ones so we don't want to be using them! Hopefully they are cores 4 & 5

Incidentally and off topic, the linuxcnc-uspace package has now migrated to Ubuntu kinetic so its available there.

If it is in Ubuntu, it should soon be in Mint, but since Mint lags quite a bit behind this can take a while.

I basically just burned the official Armbian Bullseye image, downloaded kernel source with apt, applied Preempt-RT patches from kernel.org, and built. It did definitely work, but video performance was horrible. I've read a few forum comments saying that video performance was a problem until relatively recently. On the Ubuntu image (with no RT kernel) video looks good. So I'm thinking there are some patches that Ubuntu has that Bullseye doesn't.

I've just tried the same formula on the Ubuntu Jammy image but the kernel build dies due to what appears to be a script that is getting sourced actually being an executable. I'm thinking this is something caused by the Armbian build process because their official method of building the kernel is to cross compile. So I've got a cross compilation running right now with the RT patches.

> Try isolcpus=2,3 in grub

Unfortunately that performance is with that already applied. I'm about 90% sure there is an issue with the video support. No way should X be using > 50% cpu the way it was. I guess we'll see once this kernel build finishes.

> invalid nameserver in resolv.conf

You should be able to fix that sans text editor with `echo 'nameserver 8.8.8.8' > /etc/resolv.conf`

> linuxcnc-uspace package has now migrated to Ubuntu kinetic

Now that's very good news. Once RT patches are mainlined in the kernel our lives will be much easier.

The feedback on the Odroid forum is that their preempt_rt include the graphics stuff that the default debian one won't
They are waiting for the 6.2 kernel to be released to redo it.
I read somewhere that there is some mods to the linux kernel should make it to the 6.2 kernel specifically for the Odroid N2+

I tried the echo trick but it did not stick. I think now that there is some other fault preventing apt to work on the kernels I tried.
Ubuntu did not boot
Bullseye gets in an endless loop loading USB stuff, and never gets to a login screen
Only sid and bookworm got to a log on screen but neither could use apt to install anything.
 

> their preempt_rt include the graphics stuff that the default debian one won't

That tracks with my observation. I'm building tobetter's 5.15 RT kernel on their Ubuntu Server 2022.04 image right now. Hopefully that will go better.

I just saw some good news pop up on Hacker News. The Preempt-RT patches have been accepted into Ubuntu.

ubuntu.com/blog/real-time-ubuntu-is-now-generally-available

Apparently it's part of their insane Ubuntu Pro plan now, but there is a free version of that.