bug#25148: 25.1; Slow scrolling with emacs 25.1 and Windows 10.

[Eli Zaretskii]

> From: Kristiyan Kanchev <skrechy@gmail.com>
> Date: Fri, 9 Dec 2016 11:22:08 +0200
> 
> When I decided to upgrade to the new version of Emacs - 25.1 I started
> getting very slow text scrolling. With all my packages loaded and in
> Python mode emacs is completelty unusable because there is a about half
> a second delay after every down arrow press.
> 
> Moreover, I then tried emacs -Q and opened my init.el. Pressed on the
> down arrow key and holding it caused sluggish scrolling when the cursor
> reaches somewhere around the half of the init.el.
> 
> I have also run the profiler while in emacs -Q and init.el:
> 
> - command-execute 2337 96%
> - call-interactively 2337 96%
> - funcall-interactively 2311 95%
> - next-line 1991 82%
> - line-move 1991 82%
> - line-move-partial 1356 56%

Sounds like some issue with fonts.  Does it help to set
inhibit-compacting-font-caches to a non-nil value?