bug#31138: Native json slower than json.el

[Alex Gramiak]

Dmitry Gutov <dgutov@yandex.ru> writes:

> On 22.04.2019 22:52, Alex Gramiak wrote:
>> The following might work, though I'm not
>> sure how applicable this is now to the jansson library:
>
> Peformance patches are 200% better when they come together with benchmark
> results.

Right, I should have explained: I meant that since AFAIU the size of
json_int_t is usually going to be the same size as EMACS_INT, the same
code will usually be generated for json.c. It might bring a very slight
benefit to other parts of Emacs, but not worth fussing over.

I tried making a couple patches in other areas to json.c that I hoped
would slightly improve performance, which I'll include here for
posterity. The first one uses json_dumpb over json_dumps, but from what
I can tell using it is either slower or just within error. The second
uses the *_nocheck functions where applicable, but the results seemed to
be quite similar. I suppose this means that jansson's utf-8 checking is
performant.


Benchmark for the first patch:
  (setq v ["\nasdфыв\u001f\u007ffgh\t"])
  
  (progn (garbage-collect)
         (benchmark-run-compiled 100000
           (json-serialize v)))

Results for the first patch: 1.1050s applied vs. 1.1078s without.

json-dumpb.diff
Description: json_dumpb

Benchmark for the second patch:

  (setq v (with-current-buffer (find-file-noselect
                                "~/emacs/test/src/json-tests.el")
            (vector (buffer-substring-no-properties (point-min)
                                                    (point-max)))))

    (progn (garbage-collect)
           (benchmark-run-compiled 1000
             (json-serialize v)))
           
Results for the second patch: 0.7815s applied vs. 0.7962s without.

json_*_nocheck.diff
Description: nocheck