Re: c-mode eats resources?

[storm@cua.dk (Kim F. Storm)]

Juri Linkov <juri@jurta.org> writes:

>>    Apparently, C mode constantly uses processor time even nothing is
>>    done in the buffer.  E.g. if I open a C file in Emacs and go to a
>>    different desktop and start `top' there, it shows Emacs in the
>>    first few lines with 3--7% usage of CPU.  This cannot be right.
>>    Can anybody reproduce this?
>
> This problem can be reproduced with the following code evaluated
> on a buffer in C mode:
>
> (let ((start (float-time)))
>   (font-lock-mode 1)
>   (jit-lock-fontify-now (point-min) (point-max))
>   (- (float-time) start))
>
>> Did you customize font-lock related stuff to use potentially
>> inefficient regexps?
>
> I don't know whether due to very inefficient regexps or not, but in
> the last few months fontification in C mode deteriorated drastically.
> Evaluating the code above on alloc.c using `emacs -q --no-site-file'
> on 1GHZ in different Emacs versions produces the following results:
>
> GNU Emacs 21.4 - 0.5 sec
> CVS 2004-04    - 3.5 sec
> CVS 2005-09    - 6.8 sec
> CVS 2006-02    - 10.0 sec
>
> Given a few percents of CPU utilization, no wonder that stealth
> fontification lasts several minutes.

Does it help to increase the size of the regexp cache in search.c?

#define REGEXP_CACHE_SIZE 20

-- 
Kim F. Storm <storm@cua.dk> http://www.cua.dk