Re: cc-mode fontification feels random

[Alan Mackenzie]

Hello, Eli.

On Fri, Jun 11, 2021 at 21:22:56 +0300, Eli Zaretskii wrote:
> > 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:

How many buffer lines were in your window?

>   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.)

What does adequate mean?  With those timings, the font-locking would keep
up with an auto-repeated C-v at around 30 repetitions per second.

[ .... ]

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

-- 
Alan Mackenzie (Nuremberg, Germany).