Re: emacs rendering comparisson between emacs23 and emacs26.3

[Ulrich Mueller]

>>>>> On Fri, 27 Mar 2020, Richard Stallman wrote:

>> It's not possible.  Bidirectional editing support in Emacs is
>> unconditional, it isn't an optional feature.

> It isn't optional _now_ but maybe there is an opportunity to optimize
> redisplay if the userssays "no BIDI".

> Maybe some of the pre-bidi code could be brought back and used
> when the user says there is no BIDI in the buffer.

>> What I would suggest is to compare with Emacs 24.1, which already
>> supported bidi.

> It would be interesting to compare 24 and 23, to see what slowdown
> there is.  And compare other subsequent versions to see what slowdown
> there is.  These could give hints for what operations are worth trying
> to optimize.

I've run the benchmark for several Emacs versions, on a Thinkpad L580
from 2018 (Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz). In all cases, I
used xdisp.c from version 26.3 as the test file.

  18.59        n/a    0.320
  23.4       5.436    1.019
  24.5      25.482    1.636
  25.3      22.370    1.610
  26.3      16.533    1.911
  27.0.90   17.602    2.339

First column is the version, second and third column are the times with
font-lock-mode enabled and disabled, respectively.