bug#14838: 24.3.50; repeating next-line or previous-line is broken

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Date: Wed, 10 Jul 2013 23:29:12 +0200
> 
> Starting with revision 113314, I observe the following:
> 
> 0. emacs -Q
> 1. C-h n to visit NEWS
> 2. Type C-n and hold the keys down to repeatedly move point down one line.
> 
> At around line 250, the motion gets jerky and then appears to stop, and
> the cursor disappears.  After releasing the keys (but with a delay of
> maybe a second or longer, perhaps depending on how long they were held
> down), the cursor reappears on a line further down (which one seems to
> depend on how long the keys were held down).  Subsequently holding down
> C-n or C-p makes the cursor vanish and motion stop almost immediately,
> until the keys are released.  The same thing happens if, after step 1
> above, I type M-> and then hold down C-p (the stop seems to happen a bit
> later, maybe after moving up about 300 lines).
> 
> With the revision 113360 (this one), the misbehavior begins almost
> immediately with C-n, though with C-p it appears to be the same as
> above.
> 
> When the motion starts getting jerky, my CPU load starts shooting up,
> and hits 90%+ when the cursor disappears and motion stops, and stays at
> that load until the cursor reappears at the new location.
> 
> My processor is an AMD Sempron 3400+ (64bit) with a maximum speed of
> 1.8GHz.  In addition to the following system information, my desktop
> environment is KDE 4.9.5.  My default font with emacs -Q is 
> xft:-unknown-DejaVu Sans Mono-normal-normal-normal-*-15-*-*-*-m-0-iso10646-1

Does using a different font change anything?

To see which function takes most of the time, please use
profiler-start, press C-n, then after you see CPU load for some time,
invoke profiler-report.  It is best to do that after manually loading
simple.el in source form.

Also, apply the patch I sent in
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=14836#8 and post the
contents of *Messages* after leaning on C-n for some time in this
situation.

I also asked to try reducing the keyboard auto-repeat rate, and see if
that makes any difference.

Thanks.