bug#31138: Native json slower than json.el

[Eli Zaretskii]

> Cc: sebastien@chapu.is, yyoncho@gmail.com, 31138@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Mon, 22 Apr 2019 14:46:20 +0300
> 
> > FWIW, I have stream_get.part.3 in my profiles that takes almost twice
> > the time as decode_coding_utf_8, and various lex_* and other functions
> > also quite high on the profile, with 1.5% to 3.5%.  So it isn't like
> > libjansson is tenfold faster than our code.
> 
> I don't see that in mine.

I don't know why.  In my profiles I enlarged the iteration count to
100, and also enlarged the sampling frequency.  Maybe that's the
reason.  The percentage taken by decode_coding_utf_8 didn't change as
result, FWIW.