Re: Low redisplay performance (23 regression)

[YAMAMOTO Mitsuharu]

>>>>> 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
                                address@hidden