[arch-general] CPU spikes when lid closed

[David Rosenstrauch]

I've been having an odd problem.

My laptop works like a charm on its own.  However, when it's connected 
to a USB-C dock and screen, suddenly apps that were working great start 
eating up lots of CPU.  (Such as Firefox, Thunderbird, and Zoom.)

After a bit of debugging, I realized that the issue isn't even whether 
I'm connected to the dock, but rather whether the laptop lid is open or 
closed:  close the lid and all those apps eat up CPU; open the lid and 
CPU drops and everything is groovy.

I can't for the life of me figure out what's causing this, and my 
searching hasn't been able to turn up a clear cause or solution.  Would 
anyone happen to have experienced the same issue, or be able to point me 
in the right direction as to the cause?

I'm running XFCE, with the display settings set to "mirror displays" 
(i.e., the internal laptop screen and the external HDMI monitor).

Thanks,

DR