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 …