advanced_system_tuning.md

Advanced system tuning

Warning

This is optional! Proceed with caution and at your own risk!

Check and acknowledge the logical topology of your particular SoC setup, on the PNG image generated

sudo apt update && sudo apt install hwloc -y

lstopo --logical --output-format png > `hostname`.png

Check and acknowledge the pinout of this GPS HAT

• GPS Expansion Board from Uputronics: https://pinout.xyz/pinout/uputronics_gps_expansion_board

Improve Chrony process priority, using systemd

Due to the Chrony software has not the mechanism to reduce itself its nice process value, we'll force it through systemd:

sudo sed -i '/[Service]/a Nice=-10' /usr/lib/systemd/system/chrony.service

sudo systemctl daemon-reload

sudo systemctl restart chrony

Disable and stop unnecessary services, reducing cpu time consumption, latency and jitter

sudo systemctl disable --now alsa-restore.service

sudo systemctl disable --now alsa-state.service

sudo systemctl disable --now alsa-utils.service

sudo systemctl disable --now apt-daily-upgrade.timer

sudo systemctl disable --now apt-daily.timer

sudo systemctl mask apt-daily-upgrade.service

sudo systemctl mask apt-daily.service

sudo systemctl disable --now avahi-daemon.service

sudo systemctl disable --now bluetooth.service

sudo systemctl disable --now bthelper@.service

sudo systemctl disable --now triggerhappy.service

sudo systemctl disable --now rpi-display-backlight.service

sudo systemctl disable --now systemd-timesyncd.service

sudo systemctl disable --now wpa_supplicant.service

sudo systemctl disable --now x11-common.service

Allocate the strictly minimum RAM from GPU to the OS system, as running headless

Add this to your /boot/firmware/config.txt file under the [ALL]section:

# Allocates the base minimum gpu memory, as running headless
gpu_mem=16mb

De-activates sound, aiming less resources and latency expected, as running headless

Change this on your /boot/firmware/config.txt file, to:

# De-activates sound, aiming less resources, fewer latency and interferance expected, for a headless server
dtparam=audio=off

Auto-restart 10 seconds after a Kernel panic

The Raspberry Pi OS does not have this setting, useful in extreme cases, forcing a full system restart.

echo "kernel.panic = 10" | sudo tee /etc/sysctl.d/90-kernelpanic-reboot.conf >/dev/null

Remove the unneeded support for 2G/3G/4G/5G modems

sudo apt remove --purge modemmanager -y

sudo apt autoremove --purge -y

Disable the support for Swap

sudo nano /boot/firmware/cmdline.txt

Add this noswap, after this rootfstype=ext4, and save.

Disable sdcard swapping for improving its lifespan and reducing unnecessary I/O latency

sudo dphys-swapfile swapoff

sudo dphys-swapfile uninstall

sudo update-rc.d dphys-swapfile remove

sudo reboot

Reducing ethernet coalescence on RX and TX

Every ethernet adaptor uses the coalescence method to gather packets and sent them on a bulk, for better thoughput efficiecy.

But this method introduces valuable latency and jitter on NTP or PTP-E2E packets.

Check the defaults:

sudo ethtool -c eth0

Coalesce parameters for eth0:
Adaptive RX: n/a  TX: n/a
stats-block-usecs: n/a
sample-interval: n/a
pkt-rate-low: n/a
pkt-rate-high: n/a

rx-usecs: 49
rx-frames: n/a
rx-usecs-irq: n/a
rx-frames-irq: n/a

tx-usecs: 49
tx-frames: n/a
tx-usecs-irq: n/a
tx-frames-irq: n/a

rx-usecs-low: n/a
rx-frame-low: n/a
tx-usecs-low: n/a
tx-frame-low: n/a

rx-usecs-high: n/a
rx-frame-high: n/a
tx-usecs-high: n/a
tx-frame-high: n/a

CQE mode RX: n/a  TX: n/a

Both rx-usecs and tx-usecs have the value "49" microseconds. For reference, an Intel i225-LM network card, has rx-usecs of "3" microseconds.

We'll set both to the mininum accepted by the Rpi 5B ethernet driver:

sudo ethtool -C eth0 tx-usecs 4

sudo ethtool -C eth0 rx-usecs 4

To revert to the default values:

sudo ethtool -C eth0 tx-usecs 49

sudo ethtool -C eth0 rx-usecs 49

This could shave circa 40 usecs of response time over the chrony ntpdata statistics. Huge improvement on a NTP setup that has hardware timestamping and its higher accuracy.

Setting with persistance through a systemd Service

Create the systemd service configuration file:

sudo nano /etc/systemd/system/eth-coalesce.service

Insert the following settings in it:

[Unit]
Description=Configure Ethernet interface Coalesce setting using ethtool
After=network.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/sbin/ethtool -C eth0 tx-usecs 4 rx-usecs 4
ExecStop=/usr/sbin/ethtool -C eth0 tx-usecs 48 rx-usecs 48
 
[Install]
WantedBy=multi-user.target

Enable the service and start it:

sudo systemctl enable eth-coalesce.service

sudo systemctl start eth-coalesce.service

Chrony temperature compensation - turning the your Rpi 5B into a quasi-TCXO

Using this python code, I made a fast and empirical follow-up of the system clock frequency reported by chrony tracking over a range of temperatures, between 45ºC and 61ºC. Noticed a function minimum around 52ºC.

So, I traced the relationship data between CPU temperature and the system clock frequency, using this bash code, over several hours.

For better accuracy, I created a hystheric temperature cycle using the fan control overlays, on /boot/firmware/config.txt:

## New testing Pi 5B PWN fan control setpoints - your mileage may vary
dtparam=fan_temp0=48000
dtparam=fan_temp0_hyst=4000
dtparam=fan_temp0_speed=75

dtparam=fan_temp1=53000
dtparam=fan_temp1_hyst=6000
dtparam=fan_temp1_speed=125

dtparam=fan_temp2=56000
dtparam=fan_temp2_hyst=5000
dtparam=fan_temp2_speed=200

dtparam=fan_temp3=60000
dtparam=fan_temp3_hyst=5000
dtparam=fan_temp3_speed=250

Then, fitted a quadratic curve to the data and calculated the system clock correction with a 0.5ºC resolution, using a spreadsheet.

Replaced the data within /etc/chrony/chrony.tempcomp file, previously created, and restarted chrony.

Is quite clear the adjustment of temperature compensation:

Enable support for PTP Hardware Clock (PHC) on the Ethernet chip

Raspberry Pi 5 has a PTP clock within the Ethernet chip, so we leverage that to have another high performance reference clock in Chrony.

As chronyd does not synchronise the NIC clock, it assumes the clock is running free. So, we need to use ptp4l and phc2sys to sync the PHC with the system time.

sudo apt update && sudo apt install linuxptp -y

Create a new file /etc/linuxptp/ptp4l.conf just with this:

sudo nano /etc/linuxptp/ptp4l.conf

[global]
# Only syslog every 1024 seconds
summary_interval 10

# Increase priority to allow this server to be chosen as the PTP grandmaster.
priority1 10
priority2 10

[eth0]
# My LAN does not have hardware switches compatible with Layer-2 PTP, just Layer-3 PTP.
network_transport UDPv4
delay_mechanism E2E

Create a systemd service for ptp4l:

sudo nano /etc/systemd/system/ptp4l.service

Add this:

[Unit]
Description=Precision Time Protocol service
Documentation=man:ptp4l
After=network-online.target

[Service]
Type=simple
ExecStart=/usr/sbin/ptp4l -f /etc/linuxptp/ptp4l.conf
Nice=-10

[Install]
WantedBy=multi-user.target

Then, enable and start the ptp4l service:

sudo systemctl enable --now ptp4l.service

Create a systemd service for phc2sys:

sudo nano /etc/systemd/system/phc2sys.service

[Unit]
Description=Synchronizing PTP Hardware Clock from system time
Documentation=man:phc2sys
After=ptp4l.service

[Service]
Type=simple
ExecStart=/usr/sbin/phc2sys -s CLOCK_REALTIME -c eth0 -w -u 1024
Nice=-10

[Install]
WantedBy=multi-user.target

Then, enable and start the phc2sys service:

sudo systemctl enable --now phc2sys.service

Add this new refclock into the

sudo nano /etc/chrony/chrony.conf

refclock PHC /dev/ptp0 tai refid PHC poll 0

Check under the sources that your new refclock is working properly.