Re: Odd slowness in grep and dired modes

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 20 Mar 2014 23:10:52 -0700 (PDT)
> From: Smith_RS <rsmithpv@gmail.com>
> 
> This is for NT Emacs 24.3.1 running on Windows 7.
> 
> I found a situation where NT Emacs will slow to a crawl and consume high CPU cycles, the common behavior is directory browsing in dired or file browsing in grep-mode where the mouse-over behavior is being used. I ran the profiler and saw that all the time is spent in mouse-fixup-help-message.
> 
> Steps to duplicate:
> 
> - Open dired on a directory with a non trivial number of files (20 or more).
> - Run the mouse over the files without selecting anything, just let the mouse-over behavior happen.
> - Do this with profiling turned on and observe thousands of calls to mouse-fixup-help-message.
> 
> Alternately:
> 
> - Use grep-mode to search for a string that occurs in a large number of files.
> - Continue as above.

What exactly "slows to a crawl" in these situations?

I tried the first scenario, in a very large directory, and all I could
see that moving the mouse constantly over the file names makes a
single execution unit occupied by 27%.  I see no particular slow-down,
but since Emacs does nothing but display tooltips, I'm not sure what
operations would be slow in this scenario.

mouse-fixup-help-message generates the text for the tooltip shown when
you have the mouse above the file name, so it is called whenever you
move the mouse to another file.