[pypy-dev] CFFI: better performance when calling a function from address

[Dimitri Vorona]

Hi guys,

thanks for your replies. 250ns sounded like a lot, and apparently it was. I
can't reproduce it anymore.

Thanks for the confirmation that API and ABI modes should have the same
performance. I looked at the jitlog, and both api, abi and cast pointer
seem to produce exactly the same code (assuming I bind the function to its
own variable).

Cheers,
Dimitri.

On Wed, Sep 26, 2018 at 11:05 PM Armin Rigo <armin.rigo at gmail.com> wrote:

> Hi Carl Friedrich,
>
> On Wed, 26 Sep 2018 at 22:28, Carl Friedrich Bolz-Tereick <cfbolz at gmx.de>
> wrote:
> > Couldn't that slowness of getattr be fixed by making the lib objects eg
> use module dicts or something?
>
> If we use the out-of-line API mode then ``lib`` is an RPython object,
> but if we use the in-line ABI mode then it's a pure Python object.
> More precisely it's a singleton instance of a newly created Python
> class, and the two extra instructions are reading and guard_value'ing
> the map.
>
> It might be possible to rewrite the whole section of pure-Python code
> making the ``lib`` for the in-line ABI mode, but that looks like it
> would be even slower on CPython.  And I don't like the idea of
> duplicating---or even making any non-necessary changes to---this
> slightly-fragile-looking logic...
>
> Anyway, I'm not sure to understand how just a guard_value on the map
> of an object can cause a 250 ns slow-down.  I'd rather have thought it
> would cause no measurable difference.  Maybe I missed another
> difference.  Maybe the effect is limited to microbenchmarks.  Likely
> another mystery of modern CPUs.
>
>
> A bientôt,
>
> Armin.
>
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