mrcowhead
Posts: 2
Joined: Fri Jun 05, 2020 10:30 pm

Pi 4 WiFi bit rate dropping exactly every 1 minute

Fri Jun 05, 2020 10:35 pm

I just received a Pi 4 2GB today. Everything is working great except for the wifi. I'm connected to a 5ghz AC network. It connects fine and the connection never disconnects, but exactly every 1 minute the bit rate will drop from 200mbps to 25mbps and stay there for ~5 seconds then return back to 200mbps. For my use case, I need the high bit rate to be maintained and the drops are killing me. No other device on my network is experiencing this problem. Ethernet works perfectly.

Any ideas what might be causing this issue?

Info:
- Running latest Raspian 32 bit with latest packages installed
- Tried switching the channels my wifi access point is broadcasting on
- Tried disconnecting every other device on my wifi network

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Joined: Sat Jul 30, 2011 7:41 pm

Re: Pi 4 WiFi bit rate dropping exactly every 1 minute

Fri Jun 05, 2020 11:10 pm

Might be worth turning off bluetooth - might be doing a BT scan and because they use the same aerial that might be causing problems. Just a guess though. Or it might be a normal wireless scan for AP's or similar. Might be options to change that value to help narrow down the issue.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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rpi4.local
Posts: 25
Joined: Thu Jun 04, 2020 8:20 am

Re: Pi 4 WiFi bit rate dropping exactly every 1 minute

Sat Jun 06, 2020 7:40 am

Have a look at Kismet. It's a tool to passively record all wifi packets. Record packets for a few minutes, then compare the moment when your link speed is dropping to the same moment in Kismet and see, what is actually going on in the air around you. If this is exactly every minute, there has to be an activity you can identify with Kismet as there must be a reason, why the Pi 4 needs to reduce transfer speed.

https://en.wikipedia.org/wiki/Kismet_(software)

mrcowhead
Posts: 2
Joined: Fri Jun 05, 2020 10:30 pm

Re: Pi 4 WiFi bit rate dropping exactly every 1 minute

Sat Jun 06, 2020 1:46 pm

Hey all, thanks so much for the help!

jamesh your thought about periodic wireless AP scan was spot-on. Using the `iw event` command I was able to see wifi scans were occurring at exactly the same time as the bit rate drops every 1 minute.

I did a bit of research and discovered a bunch of other people were having the same problem with wpa_supplicant on pi. The scans were causing network issues but there doesn't seem to be a way to change the interval or disable scans.

My solution was to disable wpa_supplicant and use networkmanager instead. Since then I've seen zero issues.

Thanks again for the help!

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 26695
Joined: Sat Jul 30, 2011 7:41 pm

Re: Pi 4 WiFi bit rate dropping exactly every 1 minute

Sun Jun 07, 2020 11:16 am

Had this from our GUI guy.
"The scan interval is a config parameter. If he adds the following fields to the Config section inside the dhcpcdui section of .config/lxpanel/LXDE-pi/panels/panel

BgScan=xxx
BgScanMenu=xxx

they control how often a scan takes place. Value is in ms, so 60000 is scan once a minute. BgScan is how often it scans when the wifi menu is closed; BgScanMenu is how often it scans when it is open (more frequent to find networks faster)."
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed.
I've been saying "Mucho" to my Spanish friend a lot more lately. It means a lot to him.

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