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I am using my pi4 as a portable dev server which I ssh into from a Chromebook over my home WiFi network.

What I'm seeing is that the character latency is very high, seriously impacting my developer experience. I've tried using mosh, which helps slightly, but introduces other issues, so is not the answer.

Is there anything I can do to improve ssh/WiFi latency, or even simply diagnose where the latency is arising? Is there a possibility of connecting my Chromebook to the pi4 using USB and running a serial terminal session?

pinoyyid
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4 Answers4

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You could always just plug the pi into the USB-C port and SSH in that way.

The USB-C can be used to turn the Pi4 into an ethernet device, I've written up instructions on how to set it up here:

https://www.hardill.me.uk/wordpress/2019/11/02/pi4-usb-c-gadget/

hardillb
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This answers only one part of your question. For debugging on a serial terminal session you need an USB to serial adapter cable as shown at USB to TTL to UART RS232 COM Cable module Converter. This is very inexpensive but they have very long delivery times from China. You can find also adapters from Adafruit but much more expensive.

You can also use a simple ethernet cable to connect wired to the RPi 4B.

About WiFi latency you may try to look with a network sniffer. On a terminal console you can use tcpdump.

Ingo
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I've been struggling with various issues to do with ping times and latency on my Pi 4.

Essentially the ping time will spike from a norm of 2-3ms to a single 200-900ms ping every 7-10 seconds. After quite a lot of investigation I found a cure; dramatically reduce the latency of the kernel scheduler.

To try it out first run:

sudo sysctl kernel.sched_min_granularity_ns

This will print the current value (probably 2250000)

Now:

sudo sysctl -w  kernel.sched_min_granularity_ns=100000

will set it to a lower value until you reboot.

If it works for you then this will make it persist across reboots:

echo kernel.sched_min_granularity_ns = 100000 | sudo tee -a /etc/sysctl.d/local.conf
lbt
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I am not raspberry user, but i struggled with high ssh latency between two notebooks via wifi. I reduced from 500ms to 3ms via -> you should disable
powermanagement on wifi nic on both sides.

 sudo iwconfig wlp3s0 power off
Alex
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