I'm exploring pypy's code so as to speed up callbacks from C code, so as
to speed up sqlite module's UDF.
I have some questions:
- What are the differences between ctypes, rawffi and ffi. Where
should each one of them be used?
- I see that ctypes is build on top of rawffi and ffi. If one wishes to
work around ctypes (so as to not have ctype's overhead) which of the
rawffi or ffi should he use? Which of the two is faster at runtime?
- How can i create a null pointer with _ffi?
And some remarks:
By only modifying pypy's sqlite module code, i managed to speed up
sqlite's callbacks by 30% (for example there is a "for i in
range(nargs)" line in _sqlite3. _convert_params, which is a hot path).
Also the following line in _ctypes/function.py ._wrap_callable
args = [argtype._CData_retval(argtype.from_address(arg)._buffer)
for argtype, arg in zip(argtypes, args)]
Occupies a large percentage of the overall callback time (around 60-70%).
Assuming that pypy JITs all of the above callback code. Is it a problem
having all these memory allocations for each callback (my test does 10M
callbacks)? Is there a way to avoid as much as possible all these memory
allocations.
Right now CPython runs my test (10M callbacks) in 1.2 sec and pypy needs
from 9 to 14 secs. I suspect that the large spread of pypy's run times
are due to GC.
Thank you in advance for your answers.
lefteris.
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