#emacs I was experiencing freezes of sometimes up to 30 seconds about 3/4 of the the time when I used my muscle memory to hit "undo", which I do as part of my regular "kill-line undo" combo. Something must have changed recently because I started to have show-stopping freezes of my emacs thread when I tried a routine "undo." I finally managed to squeeze a `toggle-debug-on-quit` and, with a bit of patience, got a C-g in during the freeze. The culprit in the resulting stack trace was my global undo-tree mode, which in combination with my other settings must have started failing. I turned it off by removing the line in my init.el and also running `global-undo-tree-mode` to toggle the mode and… far, no more funny freezes on undo. There are occasions when the undo tree is great and useful, but not at the cost of sometimes completely being a show stopper.