Re: bug-reference-prog-mode slows down CC Mode's scrolling by ~7%

[Alan Mackenzie]

Hello, Eli.

On Sat, Sep 04, 2021 at 18:48:12 +0300, Eli Zaretskii wrote:
> > Date: Sat, 4 Sep 2021 15:43:40 +0000
> > Cc: monnier@iro.umontreal.ca, emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>

> > > > Indeed.  With jit-lock-chunk-size at 2000, time-scroll on xdisp.c takes:

> > > > (current code): 16.4s
> > > > (new proposed code): 16.1s

> > > > ..  This speed up may well be particular to CC Mode.

> > > > Let's try jit-lock-chunk-size at 8000:

> > > > (current code): 15.1s
> > > > (new proposed code): 15.1s

> > > > ..  So, yes, it would seem a larger chunk size is advantageous for CC
> > > > Mode.

> > > How large (in lines and columns) is your window?  The above numbers
> > > are only meaningful with the window size.

> > I'm running in a window with 65 lines and 118 columns.

> That's significantly larger than the default size.  Can you repeat
> your experiments with the default size set by "emacs -Q", for
> reference?

My previous timings were on a Linux console tty.  Moving to X, and
starting Emacs with emacs --no-desktop, I get 34 Lines and 80 columns.
With my new propose jit-lock code I get the following timings with these
jit-lock-chunk-sizes:

(500): 24.5s
(2000): 18.0s
(8000): 16.4s

..  So it would seem, at least in CC Mode, a larger jit-lock-chunk-size is
advantageous on a default size GUI Emacs, too.

I haven't measured it, but I suspect 8000 would make the display of a
single screen slower, because ~4 screens will be getting fontified per
chunk (at default screen size).  2000 might well be worth going for.

> Thanks.

-- 
Alan Mackenzie (Nuremberg, Germany).