bug#71644: 30.0.50; Severe slowdown in larger files with markers beginning in emacs 29+

[Eli Zaretskii]

> From: Mitchell <mitchellahren@gmail.com>
> Date: Sat, 22 Jun 2024 12:03:05 -0600
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>, 71644@debbugs.gnu.org
> 
> On Sat, Jun 22, 2024 at 12:58 AM Eli Zaretskii <eliz@gnu.org> wrote:
> 
>  > > From: Stefan Monnier <monnier@iro.umontreal.ca>
>  > > Cc: Mitchell <mitchellahren@gmail.com>,  71644@debbugs.gnu.org
>  > > Date: Fri, 21 Jun 2024 17:06:31 -0400
>  > > 
>  > > >   commit 8783700b23e70874c4996908bf02c010ae6f3fe1
>  > > >   Author:     Stefan Monnier <monnier@iro.umontreal.ca>
>  > > >   AuthorDate: Tue Aug 2 10:38:53 2022 -0400
>  > > >   Commit:     Stefan Monnier <monnier@iro.umontreal.ca>
>  > > >   CommitDate: Tue Aug 2 13:06:51 2022 -0400
>  > > >
>  > > >       * src/xdisp.c (redisplay_window): Use BEG rather than hard 
> coding 1
>  > > >
>  > > > It changed the comparison operator in two places in marker.c.
>  > > >
>  > > > Curiously, the log message doesn't even mention the change in
>  > > > marker.c, which could be a sign that this change was not intended to
>  > > > be installed.  Stefan, did you intend to install it, and if so, do you
>  > > > have any comments about this bug report?
>  > > 
>  > > Hmm... can't remember why/how it ended up in the above commit.
>  > > Looks like an oversight.  But the change should be harmless: the
>  > > `eassert` should make sure that the comparison gives the same answer
>  > > either way (and AFAICT if/when the new comparison gives a different
>  > > answer from the old code, the old code will loop until it segfaults).
>  > 
>  > Mitchell, can you try reverting that change, and see if that affects
>  > performance in your case?
> 
> Eli, after Ihor and Stefan were able to reproduce it now, would it still be 
> helpful for me to do this and report
> back? I’m more than happy to if it would help in any way. 

Yes, because we still don't understand well why performance regressed
from Emacs 28 to Emacs 29.

> Also should I be replying to the renamed thread from now on? (i.e., 
> "chars==bytes (was: bug#71644: 30.0.50;
> Severe slowdown in larger files with markers beginning in emacs 29+") This is 
> my first bug report, so I’m not
> sure the etiquette, haha.

No, please keep replying with the original Subject.  That other thread
was a side issue.