So, few bits of context

  • I've got a MacBook 12" from 2017
  • It's connected to an external monitor via USB-C to a Satechi V2 dongle and then HDMI to the monitor

I'm experiencing a few things:

  1. Stuttering when I move windows (like dropping frames)
  2. Videos stutter when my mouse pointer is in motion
  3. WindowServer in Activity Monitor shoots through the roof of CPU usage when I move my mouse a lot
  4. The above is accompanied by the beach ball

See screenshot Activity monitor with high Window Server CPU usage

I've had a bit of a speedup by disabling "Displays have seperate spaces" in the System Preferences, but it's still happening. It's also slowing down game animations as when my mouse it moving, games won't animate.

Any thoughts?

  • What refresh rate and resolution is your display? – bmike Mar 21 at 21:37

If you're using an usb mouse, I've noticed that my gaming mouse causes the WindowServer to use a lot of CPU.

Turning transparency down in accessibility settings has helped quite a bit.

As of Dec 9th, 2020, it looks like it's still happening intermittently with one 4K display and my 2019 Macbook Pro.

  • 1
    After a week of troubleshooting, which included a BigSur reinstall from scratch, this advise regarding a Gaming USB mouse solved my problem. I had a Corsair M65 connected. I removed it and connected my Apple bluetooth trackpad. Voila!!! Now my WindowServer process never goes over 80% even when moving a window fast around screen ... My setup is a Macbook Retina late 2013 with two monitors connected (HDMI + Thunderbolt) with macbook in clamshell mode. – Pablo Burgos Dec 21 '20 at 15:13
  • 1
    It is funny but that's the correct answer here :) I removed my steel series mouse and everything went to normal. I don't know why this is happening and who needs to fix what but this definitely fixed the issue :D – thinklinux Feb 5 at 12:56

In my case, macOS Mojave on a MBP 13" 2015 connected to a qHD external monitor over HDMI. Logitech G305 gaming mouse.
Sometimes the fan spins up close to 4000 RPM and stays there even if I just use Finder and WindowServer shows high usage constantly.
The fix for me: disconnected the HDMI monitor, turned off the mouse, moved the mouse USB dongle to the other side, then reconnected the monitor and turned on the mouse. All was nice and quiet then.


You’re using an unaccelerated virtual monitor. Because your external monitor has no GPU to accelerate its graphics, all rendering is done on the CPU for that display. You can speed it up somewhat by going to the accessibility system preferences and turning off the opacity effect. But it’s always going to be much slower than an accelerated display.

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