From: "Ludwig, Mark" <ludwig.mark@siemens.com>
To: "help-gnu-emacs@gnu.org" <help-gnu-emacs@gnu.org>
Subject: RE: Performance problems (CPU 100%) with NULs in files
Date: Sat, 24 Sep 2011 00:20:24 +0000 [thread overview]
Message-ID: <BC5672F8AD4C054BAF167C9801500D1A510C37D4@USSLMMBX003.net.plm.eds.com> (raw)
In-Reply-To: <E1R6c5N-0007s4-N6@fencepost.gnu.org>
> 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
next prev parent reply other threads:[~2011-09-24 0:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-21 21:08 Performance problems (CPU 100%) with NULs in files Ludwig, Mark
2011-09-22 4:30 ` Drew Adams
2011-09-22 13:00 ` Ludwig, Mark
2011-09-22 5:44 ` Eli Zaretskii
2011-09-22 12:58 ` Ludwig, Mark
2011-09-24 0:20 ` Ludwig, Mark [this message]
2011-09-24 0:50 ` Le Wang
2011-09-24 6:04 ` Eli Zaretskii
2011-09-24 13:32 ` Ludwig, Mark
2011-09-24 14:15 ` Eli Zaretskii
2011-09-22 6:09 ` XeCycle
2011-09-22 12:58 ` Ludwig, Mark
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