Hi all! I've been away for a while. Because I'm currently awaiting the delivery of an Organelle, I wanted to get my brain back into the Pd world.

Since about 2015 or so, my main performance instrument has been a Raspberry Pi 2b running this kernel: https://blog.emlid.com/raspberry-pi-real-time-kernel/

I'm interested in writing about my experiences here because in researching and preparing to use the Organelle, I ran into some newer Pi OS options that claim to have good realtime perf, etc. -- specifically Patchbox OS.

However, upon running it on my 2b, I immediately noticed that it was overall quite sluggish (just logging in and using the terminal via SSH was painful) and besides which, the audio produced was unusably distorted with my USB audio device (an ancient MAudio MobilePre) no matter what I set Jack/ALSA to use.

Contrast that with Wheezy running the PREEMPT kernel. I run quite heavy patches on multiple cores responding to accelerometer and gyrometer data coming in via a USB Wifi AP using a buffer size of 128 samples, 3 frames, at 44.1kHz seemingly effortlessly with no clicks or dropouts. Granular synths, FM synths, vocal processing with long delay lines, a few Freeverb instances.

Has anybody else used or compiled the kernel for more recent OS versions/Pi models and had similar luck? I'm interested in being able to compile kernels myself so I can see if the benefits carry over to newer Pi models and/or the Organelle (if necessary).

Maybe I'm just hamstrung from the start by using such an antiquated USB device with an antiquated Pi model, since the latencies are far better in any case when using a Hat-type interface, and I shouldn't worry about it so much.

Thoughts?

@Zygomorph lsmod could offer some insights, perhaps not all the required kernel modules are being loaded. Use a here statement >> to redirect the output to a text file lsmod >> patchbox-modules.txt so you can compare the Wheezy and Patchbox kernels. ps -aux or top could also be helpful, something may just be eating up the cpu and or ram, ps is a little more useful than top since you can easily use here statements to redirect to a text file and keep a record. Comparing the kernel configs can also be helpful, generally you can find the config at /proc/config.gz, just copy it and decompress, if you have the kernel source you can also put the config there and run make menu config and get an interactive program to browse it that offers easy access to help/descriptions/references to all the kernel options and modules.

The old pi should not be a deterrent here, the Patchbox kernel may not support it well but that is not an issue for you since you want to build your own, even the bleeding edge kernel supports the old pis, you just need to sit down and figure out what is different between the two kernels/systems.

If you want to go towards custom kernels and optimizing things it might be worthwhile to investigate a more simple distro that can be more easily be stripped down, Slackware and Crux are good for this since their lack of systemd means everything is less tied together and changes in one spot have less chance of affecting other things. Linux From Scratch would not be a bad exercise for learning more if you want to go all out.