Ubuntu 18.04 systemd-udevd uses high CPU, conflict with wifi

Here's a workaround:

Immediately after booting, run the following commands:

sudo systemctl stop systemd-udevd systemd-udevd-kernel.socket systemd-udevd-control.socket
sudo systemctl start systemd-udevd systemd-udevd-kernel.socket systemd-udevd-control.socket

It worked on my Dell laptop.

I installed Ubuntu 18.04 LTS (AMD64) on my Dell XPS Studio 1340 and I was suffering the same issue. I've solved it by completely disabling Bluetooth from the BIOS. I know it isn't a solution but a workaround, but it works for me because I rarely use Bluetooth.

It looks like a bug in the kernel or systemd without a fix yet:

• Bug report thread on bugzilla.kernel.org
• Bug report on Launchpad

I think I've figured out the answer.

Run

/lib/systemd/systemd-udevd -D

should print garbage in endless loop containing ".../97-hid2hci.rules:"

If so, edit /lib/udev/rules.d/97-hid2hci.rules

and add

ACTION=="add" 

in front of line mentioned by above command.

It should be something like this (I'm using fedora 28, but the problem looked identical):

ACTION=="add", ATTR{bInterfaceClass}=="03", ATTR{bInterfaceSubClass}=="01", ATTR{bInterfaceProtocol}=="02", \
  ATTRS{bDeviceClass}=="00", ATTRS{idVendor}=="413c", ATTRS{bmAttributes}=="e0", \
  RUN+="hid2hci --method=dell --devpath=%p", ENV{HID2HCI_SWITCH}="1"

With above fix, everything works perfect on my old Dell. Hope that helps ;)