Re: Display performance degradation

["Jan Djärv" <jan.h.d@swipnet.se>]

Kenichi Handa skrev:
> In article <wlmy1iuxgi.wl%mituharu@math.s.chiba-u.ac.jp>, YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp> writes:
> 
>> I can observe significant display performance degradation on Emacs
>> 23.1.90 compared with 23.1, especially when scrolling TUTORIAL.ja on a
>> frame that uses the xft font backend.  I also observe the increase of
>> the total number of xftfont_draw calls, and a string in a single font
>> and color, which was originally displayed by one call, is now
>> unnecessarily divided into smaller units.
> [...]
>> + #if 0
>> +   /* This doesn't work if you have changed hinting or any other parameter.
>> +      We need to make a new object in every case to be sure. */
>>     for (objlist = AREF (entity, FONT_OBJLIST_INDEX); CONSP (objlist);
>>          objlist = XCDR (objlist))
>>       if (! NILP (AREF (XCAR (objlist), FONT_TYPE_INDEX))
>>   	&& XFONT_OBJECT (XCAR (objlist))->pixel_size == pixel_size)
>>         return  XCAR (objlist);
>> + #endif
>   
> I didn't notice this change because I'm using X fonts
> mainly.
> 
> In article <4B29E046.8050107@swipnet.se>, "Jan D." <jan.h.d@swipnet.se> writes:
> 
>> The basic question is why is this called so much?
> 
> If it is not known, the above code should not be commented out.
> 
>> It is a fundamental 
>> flaw in Emacs that makes it hard to add new stuff without degrading 
>> performance.  The core problem is that Emacs internally doesn't track 
>> what is changed.  So it re-evaluates faces, fonts, menus, toolbars and 
>> so on, all the time before redisplay, and 99.99% of those times, nothing 
>> has changed.  So to speed things up, we have various caches to check if 
>> things are the same as before.  But these caches cause problems 
>> elsewhere.
> 
> Those caches (including face-cache) are there because of the
> current redisplay engine (and face handling).  So, without
> fixing it (in your word, a fundamental flaw), those caches
> should not be disabled.
> 
>> For example, if a new font is added or if /etc/font.conf is 
>> changed, Emacs must be restarted because caches prevents Emacs from 
>> noticing the change.
> 
> The problem of extremely slow display is the bigger problem
> than it.
> 

How much is extremely, do you have figures?  I haven't noticed any change, 
maybe it only manifests itself for certain locales.

	Jan D.