bug#48377: 27.1; pixel-scroll-mode is unusable with popular modelines

[Eli Zaretskii]

> From: Rudi C <rudiwillalwaysloveyou@gmail.com>
> Date: Wed, 12 May 2021 16:07:35 +0430
> 
> pixel-scroll-mode has severe performance issues with some popular
> modelines, as documented on:
> 
> - https://github.com/seagle0128/doom-modeline/issues/199
> 
> - https://github.com/syl20bnr/spacemacs/issues/11549
> 
> - 
> https://www.reddit.com/r/emacs/comments/8rml8f/emacs_26_pixelscrollmode_gcs_like_theres_no/

Can you tell why you think pixel-scroll-mode is the culprit, and not
those enhanced mode-lines?  Why not ask the developers of those
mode-lines to take a look and find out why they make pixel-scroll-mode
so slow, as opposed to the default mode-line?

In any case, the profiles shown in these reports doesn't seem to point
to any problems with core facilities related to mode-line, so I'm
uncertain how to proceed with investigating this.  Would it be
possible for you or someone else to come up with a recipe starting
from "emacs -Q" and loading as few 3rd-party packages as possible,
ideally none at all?