Re: Slow movement in large buffers

[Matt Lundin <mdl@imapmail.org>]

Carsten Dominik <carsten.dominik@gmail.com> writes:

> On Mar 15, 2011, at 4:25 AM, Matt Lundin wrote:
>
>> I've been navigating the org-issues file (14000+ lines) and have found
>> movement within the file to be fairly slow. Sometimes Emacs will lock up
>> for several seconds.
>> 
>> For instance, to move from the level one heading "* Other" to "* Closed
>> issues" when the outline is folded takes over three seconds:
>> 
>> --8<---------------cut here---------------start------------->8---
>> next-line     1           3.015289      3.015289
>> --8<---------------cut here---------------end--------------->8---
>> 
>
> Wow, this is really bad.
> Could you use elp and instrument org, outline,
> and font-lock, and do that motion and report
> the results?
>

I instrumented those packages (along with next-line and previous-line)
and turned off flyspell. Unfortunately, it seems there is something else
involved, as previous-line is the only function registered by
elp-results:

--8<---------------cut here---------------start------------->8---
previous-line   1           2.524475      2.524475
--8<---------------cut here---------------end--------------->8---

This time, moving forward was faster than moving backward. The slowness
occurred when moving back from "* Other" to "* Development Tasks" in the
folded org-issues.org buffer. The movement jumped over a region
containing 4000 lines.

Since nothing from org or outline showed up in the results, I
instrumented the various functions called by previous-line. The culprit
seems to be a function written in C: vertical-motion. So this seems to
be an Emacs issue, rather than an org or outline issue.

--8<---------------cut here---------------start------------->8---
previous-line           1           2.5365349999  2.5365349999
line-move               1           2.536489      2.536489
line-move-visual        1           2.536436      2.536436
vertical-motion         1           2.508419      2.508419
font-lock-mode          1           3.7e-05       3.7e-05
line-move-partial       1           1.4e-05       1.4e-05
font-lock-default-function      1           9e-06         9e-06
window-hscroll          1           4e-06         4e-06
--8<---------------cut here---------------end--------------->8---

Best,
Matt