Re: Low redisplay performance (23 regression)

[David Reitter]

On Apr 30, 2009, at 1:05 AM, Chong Yidong wrote:

> On further investigation, I found that the problem can be solved  
> with a
> relatively safe change to handle_face_prop, so that it tells
> face_at_buffer_position what the base face id is rather than having
> face_at_buffer_position recalculate it each time the redisplay loop
> wants to display the next face (!).  I've checked in the fix.

Thanks.  Kudos to you and Yamamoto Mitsuharu for finding these problems.
In the case that I documented, I see a big speedup, so that's good.

I still see other performance problems.
This one is easier to reproduce, I hope:

Emacs -Q
open file (e.g., src/emacs.c)
(setq redisplay-dont-pause t)
Scroll down page-wise using PgDown  [about 3 seconds]

C-x 5 2, move frame to the right so that they're side-by-side
Switch back to first frame
Home, then scroll down page-wise using PgDown [about 5 seconds}

It seems to me that this slow-down happens when the same buffer is  
shown in another frame, but not if another buffer is shown.

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