The Problem

After upgrading from OSX Mavericks to Yosemite, at various points I noticed that my Mac became almost unusable, very sluggish – slow window loading, mouse movements were jerky etc.

Loading Activity Monitor, I could see that one of the core OSX services “WindowServer” was constantly hogging 20-40% CPU.

Individual

Solution

Using a little Google-Fu I stumbled across the following article on the Apple support forums. Essentially you should try (a) fixing your disk permissions (b) Resetting the System Management Controller (SMC) and (c) resetting the PRAM, in that order:

  1. Disconnect any additional/external monitors
  2. Load the “Disk Utility” application, select the drive on which OSX is installed, and then click “Repair disk permissions”. Official information on Disk Utility here.
  3. Now shut down your machine, and reset the SMC. How to reset the SMC depends on what type of Mac you have, so follow the official Apple instructions here. Make sure you boot up your machine after resetting the SMC.
  4. Now shut down again, and reset your PRAM. To reset the PRAM you need to hold the OPTION, COMMAND, P and R keys on your keyboard immediately after hitting the power button. Continue holding this key combination until you’ve heard two startup chimes, then release – you may then hear a third startup chime. If your machine now locks up and all you see is a black screen, don’t worry that’s normal. Give it some time (a couple of minutes), and then simply reboot your machine. Official information on PRAM here.

That’s it! This worked for me. Since following the above steps my machine is back to normal, and WindowServer rarely hovers above 5% CPU consumption (certainly not when idle, at least).

Leave a comment if this does/doesn’t work for you so that we can share the love. Special thanks to the post over on the Apple support forums which laid out the steps to follow: https://discussions.apple.com/thread/6623697