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Re: Lexical binding doesn't seem to be faster?


From: Hi-Angel
Subject: Re: Lexical binding doesn't seem to be faster?
Date: Sun, 10 Mar 2019 18:16:04 +0300

On Sat, 9 Mar 2019 at 18:06, Stefan Monnier <address@hidden> wrote:
> > FTR: I re-benchmarked as `(benchmark-run-compiled 10
> > (c-font-lock-fontify-region 0 (point-max)))`, and also with `emacs -Q`
> > to make sure that none of addons can interfere (I'm using
> > color-identifiers which may add an overhead to fontification).  For the
> > same reason I disabled GC (locally I too have it only enabled to run
> > at "idle time").
>
> Good (except for disabling GC, which makes the measurement different
> from "real life").
>
> > It's interesting that the difference almost disappeared:
> >
> >     nil: (7.463936164 0 0.0) (7.520960622 0 0.0) (7.526411695999999 0
> > 0.0) (7.537842362999999 0 0.0)
> >     t:   (7.617106151000001 0 0.0) (7.635044875 0 0.0)
> > (7.6383228789999995 0 0.0) (7.598431915 0 0.0)
> >
> > "nil" still seems to be faster, but it may as well be a statistical 
> > variation.
>
> It looks minor but it seems stable enough to be more than just
> statistical variation.
>
> > Either way, I'm happy, as you suggested, to look at per-function
> > overhead to see if there's any difference. Do you think it's still
> > worth it?
>
> Hard to tell.
>
> > And how do I do it though?  Shall I do (profiler-start), and
> > then evaluate the benchmark?
>
> Do (profiler-start 'cpu) before running the benchmark and
> (profiler-report) afterwards. And then C-u RET on the top line to expand
> it (recursively).

Thanks, so, I did that, and without disabling GC results look quite odd.

For "lexical-binding: t" it is:

    - ...                                        2 100%
     - list                                      1  50%
      - -                                        1  50%
       - let                                     1  50%
        - let                                    1  50%
         - while                                 1  50%
          - funcall                              1  50%
           - #<compiled 0x15833de3b0c9>          1  50%
            - c-font-lock-fontify-region         1  50%
             - c-before-context-fl-expand-region 1  50%
              - mapc                             1  50%
               - #<compiled 0x15833db80701>      1  50%
                - c-context-expand-fl-region     1  50%
                 - c-fl-decl-end                 1  50%
                  - c-literal-start              1  50%
                   - c-state-semi-pp-to-literal  1  50%
                      c-parse-ps-state-below     1  50%
       Automatic GC                              1  50%

Whereas for "lexical-binding: nil" it's just:

    - ...           1 100%
       Automatic GC 1 100%
-----

With GC disabled it looks more interesting:

"lexical-binding: t":

    - ...                                        1 100%
     - list                                      1 100%
      - -                                        1 100%
       - let                                     1 100%
        - let                                    1 100%
         - while                                 1 100%
          - funcall                              1 100%
           - #<compiled 0x1585968733a1>          1 100%
            - c-font-lock-fontify-region         1 100%
             - c-before-context-fl-expand-region 1 100%
              - mapc                             1 100%
               - #<compiled 0x158596934cbd>      1 100%
                - c-context-expand-fl-region     1 100%
                 - c-fl-decl-end                 1 100%
                  - c-literal-start              1 100%
                   - c-state-semi-pp-to-literal  1 100%
                      c-parse-ps-state-below     1 100%
       Automatic GC                              0   0%

"lexical-binding: nil":
    - ...                                                1 100%
     - funcall-interactively                             1 100%
      - eval-expression                                  1 100%
       - eval                                            1 100%
        - mytest                                         1 100%
         - let                                           1 100%
          - list                                         1 100%
           - -                                           1 100%
            - let                                        1 100%
             - let                                       1 100%
              - while                                    1 100%
               - funcall                                 1 100%
                - #<compiled 0x1580e938690d>             1 100%
                 - c-font-lock-fontify-region            1 100%
                  - font-lock-default-fontify-region     1 100%
                   - font-lock-unfontify-region          1 100%
                      font-lock-default-unfontify-region 1 100%
       Automatic GC                                      0   0%



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