Re: Long lines and bidi

[Dmitry Antipov <dmantipov@yandex.ru>]

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.

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
...
3) perf annotate scan_buffer --stdio ==>

       :                while (cursor >= ceiling_addr)
       :                  {
       :                    unsigned char *scan_start = cursor;
       :
       :                    while (*cursor != target && --cursor >= ceiling_addr)
65.74 :        526620:       movzbl (%r14),%eax
  6.46 :        526624:       cmp    %r15d,%eax
  0.17 :        526627:       je     526632 <scan_buffer+0x512>
27.33 :        526629:       sub    $0x1,%r14
  0.03 :        52662d:       cmp    %r14,%rbx
  0.19 :        526630:       jbe    526620 <scan_buffer+0x500>
       :                      ;

So, ~90% of time spent in scan_buffer is:

799                while (*cursor != target && --cursor >= ceiling_addr)
800                  ;

Dmitry