Re: Long lines and bidi

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 08 Feb 2013 20:38:24 +0400
> From: Dmitry Antipov <dmantipov@yandex.ru>
> CC: emacs-devel@gnu.org
> 
> On 02/08/2013 06:46 PM, Eli Zaretskii wrote:
> 
> > Btw, if you are serious about finding a solution to the long-line
> > display misfeature (or any other too-slow redisplay situation), I
> > generally find it necessary to do precision timing of the suspicious
> > parts of code, because otherwise it is impossible to find the actual
> > culprits.  On GNU/Linux, I use the following simple function:
> 
> Ah, please, there is a difference between 2013 and 1980.

Sorry, you lost me here.

> 1) perf record -e stalled-cycles-frontend -e stalled-cycles-backend -F 10000 [workload]
> 2) perf report --stdio ==>
> 
> 25.18%        emacs  emacs                          [.] scan_buffer
>   7.04%        emacs  emacs                          [.] bidi_resolve_weak

That's why testing redisplay on buffers which are predominantly
punctuation will give you unrealistic measurements.  (If you want to
understand why, read UAX#9.)

> So, ~90% of time spent in scan_buffer is:
> 
> 799                while (*cursor != target && --cursor >= ceiling_addr)
> 800                  ;

Which cannot be optimized.