Re: cc-mode fontification feels random

[Eli Zaretskii]

> Date: Fri, 11 Jun 2021 16:11:19 +0000
> Cc: Daniel Colascione <dancol@dancol.org>, rudalics@gmx.at,
>   monnier@iro.umontreal.ca, rms@gnu.org, emacs-devel@gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> I have measured CC Mode's scrolling performance using:
> 
> (defmacro time-it (&rest forms)
>   "Time the running of a sequence of forms using `float-time'.
> Call like this: \"M-: (time-it (foo ...) (bar ...) ...)\"."
>   `(let ((start (float-time)))
>     ,@forms
>     (- (float-time) start)))
> 
> together with
> 
> M-: (time-it (scroll-up-window) (sit-for 0))
> 
> on regions of text which are not yet fontified.  My window has 65 lines
> of buffer text.  Starting at the middle of xdisp.c, I see the following
> timings for the first few scrolls:
> 
>    0.026s, 0.025s, 0.026s, 0.078s, 0.026s, 0.027s.
> 
> That is, with the exception of the fourth timing, the scroll operation
> takes a little over 1/40 second.
> 
> This is in an Emacs-28 compiled with default optimisation, on a 4
> year-old first generation Ryzen machine.
> 
> For me personally, this scrolling speed, in conjunction with
> fast-but-imprecise-scrolling, is acceptable.  I also accept there are
> people with slower machines.

I suggest to compare these times with Emacs 23 to see how we
regressed.