I don't have the sources, but emacs can never keep up when I press PgDn or
PgUp in any file in any mode. This always happened to me with emacs, maybe
since the version that was released say a year ago for windows; I dont
remember what version exactly. I can confirm this bug happens in
fundamental mode, with emacs -Q, with a large text file that has no large
lines.

I have an Acer Aspire One AOD257.
Intel(R) Atom(TM) CPU N570   @ 1.66GHz, 1666 Mhz
Not sure about the display.

Oh! I dont know how to see the exact number, but the keyboard repeat rate
was set to max. I lowered it down and it solved the problem. Is it still a
bug?


2013/6/26 Eli Zaretskii <eliz@gnu.org>

> > Date: Wed, 26 Jun 2013 18:28:46 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> > Cc: 14721@debbugs.gnu.org
> >
> > [Please keep the bug address on the CC list, so this whole discussion
> > is archived by the bug tracker.]
> >
> > > Date: Tue, 25 Jun 2013 22:42:59 -0500
> > > From: Mario Valencia <mariovalspi@gmail.com>
> > >
> > > Yes, in any file.
> > >
> > > Yes, in any mode.
> > >
> > > Yes, with emacs -Q, as I said. It scrolls fine with the scroll bar
> though,
> > > as well as with "emacs -nw".
> >
> > What CPU do you have there, and what display?
> >
> > Also, can you tell what is the frequency of the keyboard auto-repeat
> > rate on that machine?
> >
> > In which version of Emacs did this start happening?
> >
> > (FWIW, I see no such slowdown on the Windows systems I work on.)
>
> Here's an experiment; let me know what you see on your machine.
>
>  emacs -Q
>  C-x C-f xdisp.c RET
>  M-x fundamental-mode RET
>
> (Use any other large file if you don't have Emacs sources, which is
> where xdisp.c comes from.)
>
> Now lean on the PgDn key, and tell me whether Emacs can keep up.
>
> On my Core i7 machine, Emacs keeps up just fine, and on average a
> single processing unit is busy 20%, i.e. there's plenty of spare
> processing power left.
>