bug#14259: 24.1; global-linum-mode slows down scrolling and user input in DocView

[Stefan Monnier]

> 2. Open a PDF that has pages you can scroll
[...]
> 5. Ensure the global-linum-mode is enabled and now scroll around/change
> pages/etc. There should be a noticeable lag that makes it very hard to use

Indeed, I can reproduce it, and it's not just a "noticeable lag" for me,
it's so dog slow that it makes you feel like Emacs is failing to respond.

> Does it help to use nlinum from GNU ELPA instead?

Yes, it's much faster.  With nlinum-mode, there is still a slowdown
(slightly more noticeable for horizontal scrolls than vertical scrolls),
but it's much less severe.
You can see the exact same slow down if you just do:

  M-: (set-window-margins (selected-window) 2) RET

So the performance cost doesn't come from nlinum-mode.
As for linum-mode, I'm not sure where the performance problem lies.


        Stefan