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Re: Low redisplay performance (23 regression)

From: Daniel Clemente
Subject: Re: Low redisplay performance (23 regression)
Date: Wed, 22 Apr 2009 17:30:37 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)

  I haven't compared Emacs 22 and 23, but from a subjective point of view I 
have noticed that latest Emacs 23 feels slow and updates too much for a modern 
computer. Some particular problems I noticed randomly:

 - if I hold C-n, I don't see the cursor while it is moving down; I only see it 
jump when I have released the key. C-p works faster. This happened when I had 
lots of CEDET buffers open (not even parsing)

 - just switching to an Emacs frame (from another window in the window manager) 
paints the screen progressively; this happens in tenths of second but so slowly 
that you can track the updated zone while it moves from top to bottom. This can 
be due to the video driver, X, window manager, …

 - sometimes, the buffer is updated noticeably two times in succession; this 
happened with org-mode files (latest org-mode from Git). This could also be 
from Org.

> Note that the most dramatic changes are due to my header line (tabbar) and 
> also
> face remapping:

  Note that tabbar lowers the performance by a large factor. It seems the 
function tabbar-buffer-update-groups is run after each keypress which involves 
a movement on the buffer, a buffer change or a message.
  Try to disable it temporarily. The problem of the visually lost C-n went away 
when I turned it off.
  To test how much it is called, something like this can be useful:

(defadvice tabbar-buffer-update-groups (before 
beep-whenever-you-redisplay-buffers activate)
(shell-command "beep -l 50")

-- Daniel

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