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Re: Low redisplay performance (23 regression)

From: YAMAMOTO Mitsuharu
Subject: Re: Low redisplay performance (23 regression)
Date: Thu, 30 Apr 2009 11:46:16 +0900
User-agent: Wanderlust/2.14.0 (Africa) SEMI/1.14.6 (Maruoka) FLIM/1.14.8 (Shij┼Ź) APEL/10.6 Emacs/22.3 (sparc-sun-solaris2.8) MULE/5.0 (SAKAKI)

>>>>> On Wed, 29 Apr 2009 14:45:41 -0400, Chong Yidong <address@hidden> said:

>>> 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.
>> As said earlier, I found that using face-remapping is highly
>> correlated with this slow-down.

> I think the problem is that lookup_basic_face computes the remapped
> face_id in an expensive way.  It needs to do some caching.

Some profiling results show that many Lisp objects are constructed in
font_clear_prop, and that causes frequent GC triggered by Lisp
evaluations in redisplay such as mode/header-line calculation.  That
would also explain why the OP doesn't observe the slowness on Emacs 22
with backported face remapping.

                                     YAMAMOTO Mitsuharu

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