[pypy-dev] Question about extension support

Armin Rigo arigo at tunes.org
Sat Mar 29 10:57:35 CET 2014


Hi Laura,

On 29 March 2014 09:52, Laura Creighton <lac at openend.se> wrote:
> Ok -- the lesson I took from this is 'ref counting hurts performance'.  Why
> was that the wrong inference to make?

No, the lession is "unoptimized refcounting hurts performance".  As
I've explained above, optimized refcounting like in CPython seems to
be good enough for almost all use cases, with the sole known exception
being some cases of gcbench.py.

I think that since this 2007 report we never were really interested
enough to know the details more precisely.  If someone wants to go to
the bottom of the question, he'd need to write an automatic optimizer
to remove most incref/decref in PyPy, and add a cycle detector.  Or do
the opposite: scrap reference counting in CPython and replace the
Py_Incref/Py_Decref with, say, shadow stack saving/restoring (search
for _du_save/_du_restore in
https://bitbucket.org/pypy/stmgc/raw/default/duhton for an example).

Either way, it looks unlikely that he'd get something that is either
simpler or more performant (here I'm ignoring CPython+Psyco which
muddles the picture).  I think that each of CPython and PyPy have
right now the kind of GC that is best suited for them.


A bientôt,

Armin.


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