[pypy-dev] cppyy use case question

[wlavrijsen at lbl.gov]

Hi Alex,

> Okay, with respect to the SWIG + pypy, works for me, and about 4x slower then
> cppyy or cpython ( which show same results more or less).

I'll try the SWIG portion later (as well as all the other points that you
raise in this thread; I think the feedback is great). First, I now have the
PyObject* tests (whew!) and that has allowed me to push the code.

Also, I found one reason why my micro-benchmark was so slow: the objects were
all kept alive (ref counting problem), meaning the number of objects to keep
track of by cpyext kept growing, thus the lookups became slower and slower.
The tests caught that. :) With that solved, micro-bench speeds are okay-ish.

Then, rewriting your example to use PyObject* directly, there is one problem:
the C++ side now needs an additional Py_IncRef (which is a function call, not
a macro, in PyPy, adding extra overhead) since it takes ownership. Keeping
the python objects alive on the python side does not work as well, since e.g.
ints are apparently not pinned down, like I thought earlier, so you may get a
fresh one with the same value on the C++ side.

Note that if you use the typedef ref_t, a selection file is needed to tell
Reflex about that typedef, or no binding will be generated for it. Alternative,
you can use PyObject* directly (which is also a typedef, but I hard-coded that
name in cppyy, together with the actual _object, for convenience).

Okay, so speeds ... It's not too bad. As discussed before, your method and
the cpyext one are mostly the same, so similar should be expected, and it is:

CPPYY
Created container
No more items

real    0m2.013s
user    0m1.931s
sys     0m0.073s

Cpython
Created container
No more items

real    0m2.722s
user    0m2.556s
sys     0m0.157s

I then tried with the fast path enabled, but clearly all the time is being
spent in cpyext, so I although it does show consistent better timings, the
difference is only 0.02 secs. Maybe that could be faster, but cpyext is an
impressive piece of work, quite a bit above my PyPy-skills. :}

Overall, I'm happy enough with the result (I'm going to need handling of
PyObject*'s later for my own nefarious purposes).

Best regards,
            Wim
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WLavrijsen at lbl.gov    --    +1 (510) 486 6411    --    www.lavrijsen.net