bug#69385: 30.0.50; Long lines with bidi text slow down Emacs

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: 69385@debbugs.gnu.org
> Date: Mon, 26 Feb 2024 16:17:53 +0100
> 
> On Mon, 26 Feb 2024 16:22:59 +0200 Eli Zaretskii <eliz@gnu.org> wrote:
> 
> >> Cc: 69385@debbugs.gnu.org
> >> Date: Mon, 26 Feb 2024 16:19:15 +0200
> >> From: Eli Zaretskii <eliz@gnu.org>
> >>
> >> > From: Stephen Berman <stephen.berman@gmx.net>
> >> > Cc: 69385@debbugs.gnu.org
> >> > Date: Mon, 26 Feb 2024 15:13:38 +0100
> >> >
> >> > On Mon, 26 Feb 2024 14:33:18 +0200 Eli Zaretskii <eliz@gnu.org> wrote:
> >> >
> >> > > The CPU is fast.  My HarfBuzz version is much older, but I doubt that
> >> > > HarfBuzz became so much slower for Arabic.  So it's very strange.  But
> >> > > maybe it's worth to try downgrading to an earlier version, just to be
> >> > > sure this is not the culprit?
> >> >
> >> > That's not so straightforward on this system, where I build system
> >> > packages from source, so downgrading HarfBuzz may require also
> >> > rebuilding packages that depend on it.  I have a somewhat older system
> >> > on this machine with HarfBuzz 7.1.0, so I can easily try that.  What
> >> > version of HarfBuzz are you using?
> >>
> >> I have 2.4.0 here.
> >
> > Btw, another possibility could be that this is specific to the Cairo
> > build.  So maybe try a build without Cairo.
> 
> I did, and the slowdown seems just as bad as in the build with Cairo.

Can you try the emacs-29 branch?