Re: Scrolling xdisp.c. Room for optimisation in syntax.c/CC Mode.

[Ulrich Mueller <ulm@gentoo.org>]

>>>>> On Sat, 18 Oct 2014, Alan Mackenzie wrote:

> I've just repeated the measurement on the Emacs trunk, with emacs -Q.  I
> now get these results:
>     no-odd-xdisp.c: 500 scrolls, total time = 104.21487808227539s.
>            xdisp.c: 500 scrolls, total time = 167.73530864715576s.

> I don't know why there are more scroll operations needed.  But the fact
> that scrolling is taking two and a half times longer in the trunk than in
> 24..3 is noteworthy, and possibly disturbing.  I'm think I compiled both
> version with the same optimisation level, etc.

I don't see such a large degradation of performance between 24.3 and
trunk here.

   no-odd-xdisp.c:
   22.3:      415 scrolls, total time = 14.469409942626953s.
   23.4:      415 scrolls, total time = 14.116178750991821s.
   24.3:      415 scrolls, total time = 45.48526978492737s.
   24.4-rc1:  415 scrolls, total time = 44.03023886680603s.
   25.0.50:   415 scrolls, total time = 45.08613348007202s.

   xdisp.c:
   22.3:      415 scrolls, total time = 14.692334413528442s.
   23.4:      415 scrolls, total time = 14.051368474960327s.
   24.3:      415 scrolls, total time = 50.858959674835205s.
   24.4-rc1:  415 scrolls, total time = 58.63706636428833s.
   25.0.50:   415 scrolls, total time = 59.3416690826416s.

Tests were done with emacs -Q -nw in an xterm, 80 columns times
80 lines.

(What causes the big slowdown from 23.4 to 24.3, though?)

Ulrich