Re: emacs rendering comparisson between emacs23 and emacs26.3

[Alan Mackenzie]

Hello, Eli.

On Sat, Mar 28, 2020 at 12:08:30 +0300, Eli Zaretskii wrote:
> > Date: Sat, 28 Mar 2020 10:09:59 +0300
> > From: Eli Zaretskii <address@hidden>
> > Cc: address@hidden, address@hidden, address@hidden

> > > It would be interesting to compare 24 and 23, to see what slowdown
> > > there is.

> > I expect an average twofold slowdown due to bidirectional support.

> Actually, I take that back: in benchmarks such as scroll-up-benchmark,
> and in a buffer with predominantly ASCII text, the effect of
> bidirectional support should be very small, perhaps 10% or 20%.

> So the issue of testing old v23.x CC Mode with newer versions of Emacs
> becomes more important than I originally thought.  Just as a teaser,
> here's the profile I obtained by scrolling in Emacs 26.3 through the
> entire xdisp.c, it seems to point to c-find-decl-spots and its
> immediate callers and subroutines as the hot spots:

Yes.  They are the functions which search for and analyse declarations.
That they take so much of the processing time is more a reflection on
the complexity of the task rather than an opportunity for optimisation.
(Which isn't to say that further optimisation is impossible, just that
it won't be easy.)

> - command-execute                                                1446 100%
>  - call-interactively                                            1446 100%
>   - funcall-interactively                                        1446 100%
>    - execute-extended-command                                    1446 100%
>     - command-execute                                            1446 100%
>      - call-interactively                                        1446 100%
>       - funcall-interactively                                    1446 100%
>        - scroll-up-benchmark                                     1446 100%
>         - let                                                    1446 100%
>          - condition-case                                        1446 100%
>           - while                                                1446 100%
>            - redisplay                                           1351  93%
>             - redisplay_internal (C function)                    1071  74%
>              - jit-lock-function                                 1064  73%
>               - jit-lock-fontify-now                             1063  73%
>                - jit-lock--run-functions                         1063  73%
>                 - run-hook-wrapped                               1063  73%
>                  - #<compiled 0x2000000008356520>                1063  73%
>                   - font-lock-fontify-region                     1061  73%
>                    - c-font-lock-fontify-region                  1061  73%
>                     - font-lock-default-fontify-region            982  67%
>                      - font-lock-fontify-keywords-region          969  67%
>                       - c-font-lock-declarations                  686  47%
>                        - c-find-decl-spots                        674  46%
>                         - #<compiled 0x20000000077e07c0>          477  32%
>                          - c-get-fontification-context            253  17%
>                           - c-looking-at-or-maybe-in-bracelist    203  14%
>                            - c-backward-token-2                   196  13%
>                             - c-backward-sws                       35   2%
>                              - c-beginning-of-macro                12   0%
>                                 back-to-indentation                 6   0%
>                           - c-backward-token-2                     16   1%

[ .... ]

-- 
Alan Mackenzie (Nuremberg, Germany).