Re: Setting bidi-paragraph-direction in comint modes

[Eli Zaretskii <eliz@gnu.org>]

> From: Chong Yidong <cyd@gnu.org>
> Cc: emacs-devel@gnu.org
> Date: Wed, 15 Feb 2012 14:24:11 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Chong Yidong <cyd@gnu.org>
> >> Cc: emacs-devel@gnu.org
> >> Date: Wed, 15 Feb 2012 08:49:18 +0800
> >> 
> >> Like I said, it's simply `ls /usr/share/doc'.
> >
> > You mean, the insertion of the next chunk of text that arrives from
> > `ls'?
> 
> Yep.

I will time this and see how frequently are we looking for the
paragraph beginning in this case.  I never tried to time repeated
insertions in small chunks, so I don't know what redisplay does in
that case.

> > I didn't look at the insertion itself, I tried the various cursor
> > motion commands _after_ the output from `ls' was already in the
> > buffer.  Do you see the "crawl" there as well?
> 
> Yep.  After inserting about 7000 lines into the *shell* buffer, as
> described, press and hold down M-v (or PageUp) for several seconds.
> Redisplay freezes, not updating until about two seconds after the key is
> released.  Then it updates the screen with the new cursor position.

I see nothing like that, the display never freezes.  Strange.  What
kind of CPU do you have there?  Is it a GUI session or a TTY session?
Does Emacs run on the local machine or remote one?

> > Can you quantify it?  Like, how much time it takes to insert the first
> > 2000 lines vs the last?
> 
> Not easily, but it is definitely not my imagination.

OK, I will do it myself.

> You can't reproduce the problem at all?

I see some slowdown, but I cannot in good faith characterize it as
anything like "crawl", and M-v doesn't get stuck.  This is on 7-year
old single-core CPU at 3GHz, in an Emacs compiled without
optimizations (-O0).  On the same machine, an optimized build (-O2)
runs significantly faster, so I see almost no slowdown at all.

If you say "ls /usr/share/doc >> foo" 4 times and then visit the
resulting file, do you see the same slow M-v in the buffer?

Anyway, please make a bug report about this, and I will see what I can
do about it.