bug#15390: 24.3; scrolling in emacs,w32 uses 100% cpu

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 16 Sep 2013 09:41:52 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 15390@debbugs.gnu.org
> 
> Emacs 24's display performance is sensitive to the paragraph length as
> well.  A paragraph start and end are defined for this purpose as empty
> lines.  Is it possible that the text files you used didn't have any
> empty lines at all?  If so, can you try files that do have empty
> lines?

In addition, the characters that begin a paragraph might be of
importance.  You say "text file", so I presume that is human-readable
text, but it could also be a file with many digits and punctuation
characters -- these make redisplay work harder.

IOW, please show some representative portion(s) of the file(s) in
question, or perhaps even the entire file, if you can share it.

> I can only see performance similar to what you report on a laptop with
> a Core i3-2328M at 2.2 GHz (running Windows 7 64-bit), a much slower
> machine.  I will try later on a desktop Windows 7 machine.

Did that, and saw 20% to 30% CPU load, on a system that is powered by
a Core 2 Duo CPU, clearly much slower than yours.

Bottom line: I'm quite sure the file(s) you are using somehow hit the
display engine in its underbelly.