Re: Low redisplay performance (23 regression)

[David Reitter <david.reitter@gmail.com>]

On Apr 22, 2009, at 11:30 AM, Daniel Clemente wrote:

>  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.

I can corroborate these observations (subjectively FWIW) with  
different modes such as SLIME and on NS (on OS X).  So I don't think  
it's anything system-related (drivers, X, etc).

>  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:

Thanks, but I don't use tabbar in this way (my branch is found here:  
[1]), so this function doesn't get called.

Note that if I run tabbar, but just set header-line-format to  
something simpler (without all those faces), then I get a substantial  
speedup.


However, the point here is that these slowdowns with tabbar, SLIME,  
org-mode and whatever did not occur in Emacs 22.  This is going to be  
bad for any user.




[1] git://github.com/davidswelt/aquamacs-emacs.git