Re: cc-mode fontification feels random

[Eli Zaretskii]

> Cc: rudalics@gmx.at, monnier@iro.umontreal.ca, rms@gnu.org,
>  emacs-devel@gnu.org
> From: Daniel Colascione <dancol@dancol.org>
> Date: Fri, 11 Jun 2021 11:02:34 -0700
> 
> >>     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.
> 
> Regression is acceptable in exchange for correctness so long as absolute 
> performance is adequate. We're not using 80486s anymore.

Here are my times using an optimized build of Emacs 27.2 on a 3.4GHz
Core i7 box:

  0.015625
  0.03125
  0.015625
  0.046875
  0.09375
  0.0625
  0.015625
  0.03125
  0.015625
  0.03125
  0.015625
  0.03125

You consider this to be adequate performance for a single
window-scroll?  (I don't have an optimized build of Emacs 28, but
there's no reason to believe it is faster; quite the opposite.)

And here's the top part of the profile while running the above
benchmark:

  - redisplay_internal (C function)                                 159  65%
   - jit-lock-function                                              158  65%
    - jit-lock-fontify-now                                          158  65%
     - jit-lock--run-functions                                      158  65%
      - run-hook-wrapped                                            158  65%
       - #<compiled -0x1ffffffff8a67860>                            158  65%
        - font-lock-fontify-region                                  157  65%
         - c-font-lock-fontify-region                               157  65%
          - font-lock-default-fontify-region                        146  60%
           - font-lock-fontify-keywords-region                      143  59%
            - c-font-lock-declarations                               97  40%
             - c-find-decl-spots                                     97  40%
              - #<compiled -0x1ffffffff94b65d0>                      73  30%
               - c-forward-decl-or-cast-1                            38  15%
                - c-forward-type                                     22   9%
                 - c-check-qualified-type                             7   2%

We can stick our heads in the sand as much as we want, but facts are
stubborn things.