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
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