Re: follow-mode: extremely slow in combination with org-mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Gerald Wildgruber <wildgruber@tu-berlin.de>
> CC: <emacs-devel@gnu.org>
> Date: Sat, 16 Jun 2018 15:06:49 +0200
> 
> 
>                    - follow-calc-win-start                     103381  64%
>                     - while                                    103381  64%
>                      - let                                     103378  64%
>                       - setq                                   103349  64%
>                        - car                                   103349  64%
>                         - follow-calc-win-end                  103346  64%
>                          - apply                               103346  64%
>                           - #<compiled 0x226e139>              103329  64%
>                            - apply                             103322  64%
>                             - #<lambda 0xe5f44dcc127a05e>             103313  64%
>                              - let*                            103310  64%
>                                 posn-point                      51699  32%
>                               + if                              51546  32%
>                               + window-inside-pixel-edges                 47   0%

There's something here I don't understand.  This profile says that
follow-calc-win-end calls posn-point via two 'apply' calls, a
byte-compiled function, and a lambda-function.  But there's nothing
like that in follow.el that I could see.  Did you advise some
functions in follow.el?  If not, what are those intermediate calls?

> > If you "show all" in the Org buffer, do the lags become significantly
> > smaller?
> 
> Yes, the difference is VERY significant; but I guess this is because
> with collapsed headings, there is A LOT more text within the boundaries
> of my frame, than with show-all.

How much is "A LOT more"?  How many physical lines do you have in
typical single window in that Org buffer?