Re: open large file with C code: is it realy should be so slow?

["Dave Milter" <davemilter@gmail.com>]

On Mon, Dec 1, 2008 at 3:37 PM, Alan Mackenzie <acm@muc.de> wrote:
>
> On Mon, Dec 01, 2008 at 01:01:08PM +0300, Dave Milter wrote:
>> I have problem with emacs responsibility,
>> I work with large enough C header files,
>> and when I want to scroll it using mouse's wheel or
>> page (up|down) keys emacs stop react on any keys, like (ctrl+g),
>> and eats 100% of CPU's time during long period,
>> I wonder is this a bug, or expected behaviour?
>
> It's a bug.
>
> Although C Mode works "properly" here, it doesn't seem to be tuned very
> well for files like this one (At91SAM9253_inc.h), which contain a lot of
> #defines and comments and nothing else.
>

I made some more testing (to find out problem in "file", or in "large"),
because of really want to see this bug fixed,

I see the same behaviour on file created by

for ((i=0;i<500;++i)); do echo "extern void f${i}(int a${i});"; done

emacs from cvs and emacs 22 show the same behaviour -
eating 100% of cpu, if make fast scrolling.

>
>> elp results are:
>

Function Name                                              Call Count
Elapsed Time  Average Time
=========================================================  ==========
============  ============
font-lock-fontify-region                                   41
230.65321899  5.6256882682
font-lock-default-fontify-region                           41
230.65264900  5.6256743658
font-lock-fontify-keywords-region                          41
230.61167599  5.6246750243
font-lock-fontify-syntactically-region                     41
0.039573      0.0009651951
font-lock-unfontify-region                                 41
0.0005050000  1.231...e-05
font-lock-default-unfontify-region                         41
0.0001930000  4.707...e-06
font-lock-extend-region-wholelines                         41
0.0001080000  2.634...e-06
font-lock-extend-region-multiline                          41
9.800...e-05  2.390...e-06
font-lock-set-defaults                                     41
8.299...e-05  2.024...e-06
font-lock-mode                                             3
7.6e-05       2.533...e-05
font-lock-default-function                                 3
1.400...e-05  4.666...e-06


In fact, with small files, for example the same script but 5000 -> 500,
I see the same situation, but after eating cpu during some period,
it never eating it after, and all works smoothly,
while with big files it eats it every fast scroll.