Re: Performance problems (CPU 100%) with NULs in files

[Le Wang <l26wang@gmail.com>]

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File a bug.  Let the powers that be decide whether is fix worthy or not.

This way even if it's closed as wont fix, at least when someone does a bug
search in the future they'll see that a similar issue has come up.

On Sat, Sep 24, 2011 at 8:20 AM, Ludwig, Mark <ludwig.mark@siemens.com>wrote:

> > From: Eli Zaretskii
> > Subject: Re: Performance problems (CPU 100%) with NULs in files
> >
> > > From: "Ludwig, Mark" <ludwig.mark@siemens.com>
> > > Thread-Topic: Performance problems (CPU 100%) with NULs in files
> > > Date: Wed, 21 Sep 2011 21:08:42 +0000
> > >
> > > What happens is that as I scroll through the file, when the NULs are
> > visible, Emacs gets into some intensive processing for a long time
> > (minutes, sometimes!).  It eventually unwinds and repaints the display,
> > but any movement of point sends it into this loop again.  I have found
> > that M-< or M-> will quickly reposition away from the problem (assuming
> > the beginning and/or end of the file do not contain NULs).  Most other
> > movement operations send it into the loop.
> >
> > Does it help to visit such files without code conversions, i.e.
> >
> >   M-x find-file-literally RET FILENAME RET
> >
> > ?
> >
> > If not, please file a bug report and attach to it an example file that
> > causes this slowdown.
>
> Thanks for the advice, but I have investigated and decided this is probably
> too unusual to expect any "fix" for it.
>
> What I have found is that the "problem" is due to a "line" of text being
> extremely long.  In the test file I have, it is ~800,000 characters (bytes).
>  (It came to me with NULs, but I can replace those with any other printable
> character and get the same result.)
>
> What I find is that some movement actions are rather slow -- take 4-7
> seconds -- while others are extremely quick.  Specifically, the "forward"
> movement actions (C-e, M-f) are slow, while the "backward" movement actions
> (C-a, M-b) are instantaneous.  Reposition (C-l) is also slow, as are the
> line-oriented commands (C-p, C-n).
>
> Thinking through the magnitude of the oddity, I don't think it would be
> reasonable to expect Emacs to handle this any better than it does.  It's
> just gratifying that C-g works, so I can interrupt it when I stumble into
> some junk, and now that I know which actions are fast and slow, I can work
> around it.
>
> OTOH, if you guys really think this is worth asking any developer to fix,
> I'll file a bug report.  I don't need to send any data, because it's easy to
> reproduce this behavior starting with an empty buffer.
>
> Thanks!
>
> Mark
>
>
>


-- 
Le

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