Bluetooth barely usable when WiFi signal is bad

julienfalque · 2025-01-13 07:16:24

Hi, I have a Dell XPS 15 9550 laptop and I have a long history of painful Bluetooth issues with it :( One of those is that when the WiFi signal is weak, the Bluetooth becomes very unstable.

I use Bluetooth for my mouse (Logitech MX Anywhere 2) and my keyboard (Logitech MX Keys). When the issue happens (e.g. closed doors that weaken the WiFi signal), the mouse becomes laggy: moving it feels less smooth, as if the refresh rate was decreased. Worse: as soon as I type something on the keyboard, the mouse freezes completely for a few seconds. The keyboard itself is unusable: it either does not work at all, or it repeats what I type indefinitely. WiFi traffic also seems to worsen things (e.g. downloading system updates will worsen the mouse lag).

If I either disable the WiFi or one of the Bluetooth device, things go back to normal and work perfectly fine. So I need to be offline or to switch between mouse and keyboard, which is far from ideal.

Rebooting sometimes fixes the issue when I'm lucky, but maybe it's because the WiFi signal got better at that moment.

Improving the WiFi signal always fixes the issues but it's not always possible and it still seems to require a reboot.

Also, if I remember correctly, I used to fix this with

sudo modprobe -r brcmfmac && sudo modprobe brcmfmac

But now this always triggers an error:

modprobe: FATAL: Module brcmfmac is in use.

I already reported this a long time ago but I thought it would be best to open a new thread now that I understand the problem a bit better.

V1del · 2025-01-13 16:31:12

It's generally normal that wifi and BT clash because they occupy the same frequency band. Depending on driver there might be some software mitigations to try and lessen the impact but generally brcmfmac is probably not the most developed out there and the more you strain the wifi signal the stronger this clash becomes.

The best way to physically mitigate this issue is switching wifi to the 5Ghz band, but this has generally less range regardless, so might drop you out of the range anyway. And of course assuming router and wifi chip have to be capable of connecting/sending that frequency.

seth · 2025-01-13 21:51:52

Bluetooth or the UR dongle?
If you have and can use the dongle switching the side where you plug it might help you out.

Also check your network config and make sure you're not constantly re-connecting, brcmfmac seems to boost wifi over BT during the dhcp window, so many dhcp requests (might also be caused by roaming) will systematically trash your bluetooth signal.

Last edited by seth (2025-01-13 21:52:05)

julienfalque · 2025-01-14 06:59:22

I don't have any dongle.

WiFi connection doesn't seem really unstable, just slow, but yes, the signal likely gets priority over Bluetooth. How could I check that?

Also, it seems things have gotten worse recently because the issue occurs much more frequently, even when WiFi signal is OK-ish.

seth · 2025-01-14 10:32:15

Please post the output of

find /etc/systemd -type l -exec test -f {} \; -print | awk -F'/' '{ printf ("%-40s | %s\n", $(NF-0), $(NF-1)) }' | sort -f

Please post your complete system journal for the boot:

sudo journalctl -b | curl -F 'file=@-' 0x0.st

You can then try to add "brcmfmac.debug=0xffffff" to the https://wiki.archlinux.org/title/Kernel_parameters what should make brcmfmac very chatty, but we'll first looks at the state of the system at large.

julienfalque · 2025-01-15 07:06:39

❯ find /etc/systemd -type l -exec test -f {} \; -print | awk -F'/' '{ printf ("%-40s | %s\n", $(NF-0), $(NF-1)) }' | sort -f
avahi-daemon.service                     | multi-user.target.wants
avahi-daemon.socket                      | sockets.target.wants
bluetooth.service                        | bluetooth.target.wants
cups.path                                | multi-user.target.wants
cups.service                             | printer.target.wants
cups.socket                              | sockets.target.wants
dbus-org.bluez.service                   | system
dbus-org.freedesktop.Avahi.service       | system
dbus-org.freedesktop.nm-dispatcher.service | system
dbus-org.freedesktop.timesync1.service   | system
dell-bios-fan-control-resume.service     | suspend.target.wants
dell-bios-fan-control.service            | multi-user.target.wants
display-manager.service                  | system
docker.service                           | multi-user.target.wants
efi-bootnext.service                     | multi-user.target.wants
efi-bootnext-sleep.service               | sleep.target.wants
gcr-ssh-agent.socket                     | sockets.target.wants
getty@tty1.service                       | getty.target.wants
gnome-keyring-daemon.socket              | sockets.target.wants
i8kmon.service                           | sys-subsystem-hwmon-devices-dell_smm.device.wants
NetworkManager.service                   | multi-user.target.wants
NetworkManager-wait-online.service       | network-online.target.wants
ntpd.service                             | multi-user.target.wants
nvidia-hibernate.service                 | systemd-hibernate.service.wants
nvidia-resume.service                    | systemd-hibernate.service.wants
nvidia-resume.service                    | systemd-suspend.service.wants
nvidia-suspend.service                   | systemd-suspend.service.wants
p11-kit-server.socket                    | sockets.target.wants
pipewire-pulse.socket                    | sockets.target.wants
pipewire-session-manager.service         | user
pipewire.socket                          | sockets.target.wants
power-profiles-daemon.service            | graphical.target.wants
reflector.timer                          | timers.target.wants
remote-fs.target                         | multi-user.target.wants
systemd-timesyncd.service                | sysinit.target.wants
wireplumber.service                      | pipewire.service.wants
xdg-user-dirs-update.service             | default.target.wants

System journal for the boot: https://0x0.st/8oMm.txt

seth · 2025-01-15 10:14:13

No colliding services.
There's no message from the wifi after the initial connecition, not even from NM scanning around (oOr complaining about the signal) - is this just because the journal is only 10 minutes?

You've a logitech MX anywhere mouse/keyboard - those came w/ a UR dongle? No?

Arch Linux

#1 2025-01-13 07:16:24

Bluetooth barely usable when WiFi signal is bad

#2 2025-01-13 16:31:12

Re: Bluetooth barely usable when WiFi signal is bad

#3 2025-01-13 21:51:52

Re: Bluetooth barely usable when WiFi signal is bad

#4 2025-01-14 06:59:22

Re: Bluetooth barely usable when WiFi signal is bad

#5 2025-01-14 10:32:15

Re: Bluetooth barely usable when WiFi signal is bad

#6 2025-01-15 07:06:39

Re: Bluetooth barely usable when WiFi signal is bad

#7 2025-01-15 10:14:13

Re: Bluetooth barely usable when WiFi signal is bad

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