[pypy-dev] Freelist in PyPy? Reuse short lived objects?

[Carl Friedrich Bolz-Tereick]

Hi Pierre,

This is not ready at all and I don't have enough time to work on it at the moment, *however*: I have a small prototype (on the branch map-improvements) that changes the instance layout in PyPy to store type-stable instances with several fields that contain ints or floats much more efficiently. It seems to give a 50% speedup on your micro benchmark, so that's promising. There's still a bug somewhere and it needs very careful investigation whether it costs too much on non-numerical programs, but potentially this is a good improvement.

Cython is not likely to help on PyPy, because the overhead of our C-API emulation is too high. A free list is also unfortunately not really workable for us, since our GC strategy is very different (we don't know when an object is freed). 

Cheers, 

Carl Friedrich

On January 14, 2021 4:34:12 PM GMT+01:00, PIERRE AUGIER <pierre.augier at univ-grenoble-alpes.fr> wrote:
>Hello,
>
>I was still playing with the idea to speedup codes using small
>numerical objects.
>
>I wrote a Cython extension which defines a Point (3d) cdef class and a
>Points cdef class (a vector of points). Both classes contain a pointer
>towards a point_ C struct:
>
>ctypedef struct point_:
>    float x, y, z
>
>Of course, any computation with Point objects with involved several
>very short lived objects and we really want to avoid all the associated
>malloc/free calls.
>
>In Cython, one can decorate a cdef class with `@cython.freelist(8)` to
>reused objects:
>https://cython.readthedocs.io/en/latest/src/userguide/extension_types.html#fast-instantiation
>
>I try to add a bit of logic to avoid freeing and allocating the memory
>for the struct
>(https://github.com/paugier/nbabel/blob/master/py/microbench/util_cython.pyx).
>If I understand correctly, doing such things is possible in CPython
>because the method __dealloc__ is called as soon as the objects is not
>accessible from Python. Or we can use the fact that it's very fast to
>get the reference count of an instance. But I think it is not the case
>for PyPy.
>
>Is there an alternative strategy efficient with PyPy?
>
>Pierre
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