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Re: Low redisplay performance (23 regression)

From: Tassilo Horn
Subject: Re: Low redisplay performance (23 regression)
Date: Wed, 29 Apr 2009 19:40:24 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)

"Tobias C. Rittweiler" <address@hidden> writes:

> David Reitter <address@hidden> writes:
>> [Emacs 23.x performance regression]
> On a related note, I notice a big slowdown for `end-of-defun'.

And on yet another related note, today I've found out that after
changing the font scale for the current buffer using `C-x C-+' or `C-x
C--' line-by-line scrolling slows down considerably.

The performance regression can be seen very good when using the smooth
scrolling package from [1], but it's also perceptible with the emacs

The performance hit seems to be harder on long and font-locked lines (as
others already noticed).  If I scroll my .emacs (~2000 loc) and come
across the custom-set-faces which have some lines with about 200
columns, with the smooth-scrolling package, the screen hangs for a
second and then I'm scrolled for some pages at once.

After setting the text scale back to default using `C-x C-0', scolling
works smooth again.

Oh, yet another observation: While writing this mail I enlarged the text
scale with `C-x C-+' and if I press and hold the up or down key, point
hangs for very short periods of time at some positions and then jumps
over some lines without visible redisplay, even though no scrolling at
all is done.  Resetting the font scale with `C-x C-0' and doing the
same, I can see that point crosses each and every line without jumps.

[1] http://www.adamspiers.org/elisp/smooth-scrolling.el

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