Re: [perl.git] branch blead, updated. v5.21.6-124-gbd30fe8

FWIW, this is based on some work I did in Sereal, where I saw a very
significant speedup for deserializing packets with lots of IV's.

Yves


On 28 November 2014 at 15:46, Steffen Mueller <smueller@cpan.org> wrote:

> In perl.git, the branch blead has been updated
>
> <
> http://perl5.git.perl.org/perl.git/commitdiff/bd30fe8921c88e4677c2279b442a56a11ae037b4?hp=de06ff5a50f29eaee3e72394fa1c2417689cac47
> >
>
> - Log -----------------------------------------------------------------
> commit bd30fe8921c88e4677c2279b442a56a11ae037b4
> Author: Eric Herman <eric@freesa.org>
> Date:   Fri Nov 28 15:08:04 2014 +0100
>
>     Speed up newSViv()
>
>     newSViv() is not used a whole lot by the core. But it is frequently
>     used in XS modules. In a nutshell, it allocates a new EMPTY SV just to
>     call sv_setiv which calls sv_upgrade which in turn spends inordinate
>     amounts of time looking at the properties of the SV to make it an
>     SVt_IV. But the properties of that SV are always the same: a clean
>     slate! Therefore, inlining the very simple bits of sv_setiv that are
>     actually necessary gives a very tangible speed-up.
>
>     It's not very easy to benchmark with with a language-level one-liner
>     because newSViv() isn't too common in the core. Thus follow XS
>     micro-benchmarks:
>
>     Benchmark 1: Virtually no-op XS function.
>
>       SV *
>       echo_integer(int in)
>         CODE:
>           RETVAL = newSViv(in);
>         OUTPUT: RETVAL
>
>       $ dumbbench -i50 --pin-frequency -- ./perl -Ilib \
>         -MXS::APItest -e 'XS::APItest::echo_integer($_) for 1..1000000'
>
>     Before: 3.2782e-01 seconds
>     After:  3.0530e-01 seconds
>
>     A small change, but considering the massive overhead of a function
> call,
>     quite surprisingly noticeable.
>
>     Benchmark 2: XS function that constructs multiple integer values.
>
>     SV *
>     echo_integer_array(int in)
>       PREINIT:
>         int i;
>         AV *av;
>       CODE:
>         av = newAV();
>         RETVAL = newRV_noinc((SV *)av);
>         av_extend(av, in-1);
>         for (i = 0; i < in; ++i)
>           av_store(av, i, newSViv(i));
>       OUTPUT: RETVAL
>
>       $ dumbbench -i50 --pin-frequency -- ./perl -Ilib \
>         -MXS::APItest -e 'XS::APItest::echo_integer_array(100) for
> 1..10000'
>
>     Before: 1.18363e-01 seconds
>     After:  0.92050e-01 seconds
>
>     While in the grand scheme of things, this might seem like a very small
>     optimization, there are many XS modules that actually generate a lot of
>     integer values, de-serializers being good examples.
> -----------------------------------------------------------------------
>
> Summary of changes:
>  sv.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/sv.c b/sv.c
> index 4a2850e..40b614e 100644
> --- a/sv.c
> +++ b/sv.c
> @@ -9359,7 +9359,22 @@ Perl_newSViv(pTHX_ const IV i)
>      SV *sv;
>
>      new_SV(sv);
> -    sv_setiv(sv,i);
> +
> +    /* Inlining ONLY the small relevant subset of sv_setiv here
> +     * for performance. Makes a significant difference. */
> +
> +    /* We're starting from SVt_FIRST, so provided that's
> +     * actual 0, we don't have to unset any SV type flags
> +     * to promote to SVt_IV. */
> +    assert(SVt_FIRST == 0);
> +
> +    SET_SVANY_FOR_BODYLESS_IV(sv);
> +    SvFLAGS(sv) |= SVt_IV;
> +    (void)SvIOK_on(sv);
> +
> +    SvIV_set(sv, i);
> +    SvTAINT(sv);
> +
>      return sv;
>  }
>
>
> --
> Perl5 Master Repository
>



-- 
perl -Mre=debug -e "/just|another|perl|hacker/"

• Re: [perl.git] branch blead, updated. v5.21.6-124-gbd30fe8 by demerphq
• Re: [perl.git] branch blead, updated. v5.21.6-124-gbd30fe8 by demerphq