Re: Performance

[Stefan Monnier]

> I'm a bit surprised, because my main machine is 5 years old, and I
> don't see any noticeable slowdown.  But then I almost never have 10
> frames (let alone more) open at the same time; usually all but 2 are
> minimized or iconified.

I think the number of frames is a key part to trigger the slowdown
(e.g. I don't notice it in the Emacs instance that runs Gnus where
I usually have only 2 or maybe 3 frames only).

Sometimes I see a significant slowdown even when only 2 frames are
"open" (typically one 80x89 plus a separate single-line minibuffer-only
frame), but with a large number of iconified frames (like 20 or more).

> Granted, I didn't yet get to profiling and optimizing the code,
> because (a) so many features need yet to get right before I get them
> fast, and (b) the current code works reasonably fast for me, even when
> I compile with -O0 and even in a buffer with text that really needs
> reordering (which I understand is not your case).

I figured as much, but thought we may want to start thinking about
performance since it can take a while to track it down (and then fix
it).

> From what you tell, it sounds like vertical cursor motion is the
> problem; please try C-f and C-b (_not_ the arrow keys!) and tell if
> they are reasonably fast or also slow.

C-f and C-b also have trouble keeping up with the repeat-rate (30/s).

> Also, what kind of files are those?

Code files, Help buffers, ... Most of them fit within 80 columns.

> Anyway, I'd love some help in this matter.  Getting the bidi code
> faster is not a trivial job, but it does not require any knowledge of
> bidirectional scripts, and I can help with understanding what the code
> does and why.  Without someone stepping forward, I doubt that I could
> get to seriously working on speeding up the code, what with merely 10
> hours a week I have to work on Emacs.

Of course.  Actually, part of the reason I posted it is so as to see if
other people have experienced performance problems.  I'm not completely
sure the problems are linked to cursor motion, to tell you the truth
(e.g. it might be linked to my systematic use of reveal-mode).
So I think we need a lot more data points in order to figure out where
the problem comes from.


        Stefan