This repository is built as part of my journey to improve Raspberry Pi4 used as Digital Streamer using USB output.

HW Supported:

• RPi4b
• Standard Async USB2.0 Audio
• Onboard ethernet

Software:

• Raspbian 11 64bit
  • stripped all running services
  • custom RT patched kernel
  • runtime kernel config optimizations (sysctl)
• RoonBridge
  • autostarted
  • • systemctl stop mpd ; systemctl start roonbridge
• MPD
  • systemctl stop roonbridge ; systemctl start mpd
• Static IP configuration
  • /etc/network/interfaces.d/eth0
  • /etc/resolv.conf
• babysit service
  • monitors and sets right affinity and priority for MPD and RoonBridge RAAT RealTime processes
• OpenSSH server

Contents:

• jitter and latency optimized Linux RT kernel configuration for Raspberry Pi4
• scripts setting priorities and CPU affinities to further improve jitter
• scripts for reviewing current affinity and priority for RT or all processes

What is running in OS after boot:

pi@rpi4strm:~ $ pstree
systemd─┬─babysit.sh
        ├─sshd
        └─start.sh───mono-sgen─┬─mono-sgen───12*[{mono-sgen}]
                               ├─mono-sgen───8*[{mono-sgen}]
                               ├─processreaper
                               └─4*[{mono-sgen}]

Measured Results:

 # rpi-usb-audio-tweaks 
During Roon payback (16@44):
root@rpi4strm:/home/pi# jitterdebugger -a 0-3 -v
affinity: 0-3 = 4 [0xF]
T: 0 ( 1599) A: 0 C:    593447 Min:         2 Avg:    2.97 Max:        59
T: 1 ( 1600) A: 1 C:    593440 Min:         1 Avg:    2.08 Max:        26
T: 2 ( 1601) A: 2 C:    593432 Min:         1 Avg:    2.07 Max:        49
T: 3 ( 1602) A: 3 C:    593425 Min:         1 Avg:    2.07 Max:        20

for comarison, jitterdebugger examples from other distros:

# VitOS:
affinity: 0-3 = 4 [0xF]
T: 0 ( 7513) A: 0 C:     83470 Min:         7 Avg:   17.58 Max:        45
T: 1 ( 7514) A: 1 C:     83450 Min:         5 Avg:   17.28 Max:        38
T: 2 ( 7515) A: 2 C:     83434 Min:         5 Avg:   17.06 Max:        49
T: 3 ( 7516) A: 3 C:     83418 Min:         6 Avg:   17.21 Max:        48

# Moode:
affinity: 0-3 = 4 [0xF]
T: 0 ( 1879) A: 0 C:     82959 Min:         7 Avg:   11.88 Max:       103
T: 1 ( 1880) A: 1 C:     82933 Min:         7 Avg:   11.53 Max:        67
T: 2 ( 1881) A: 2 C:     82907 Min:         6 Avg:   11.47 Max:        54
T: 3 ( 1882) A: 3 C:     82891 Min:         7 Avg:   11.57 Max:        57

# Raspbian11 64bit , only few services running:
affinity: 0-3 = 4 [0xF]
T: 0 (  705) A: 0 C:     94692 Min:         6 Avg:   20.17 Max:        97
T: 1 (  706) A: 1 C:     94664 Min:         6 Avg:   19.97 Max:        43
T: 2 (  707) A: 2 C:     94636 Min:         5 Avg:   20.16 Max:        44
T: 3 (  708) A: 3 C:     94620 Min:         6 Avg:   21.25 Max:        71

Detailed per-cpu core viee of jitter performance:

Comparison chart of jitter across various RPi4 OSes