New submission from STINNER Victor:
While testing issue #29464 patch, I failed to see a major enhancement on the
stack usage of fast calls without keyword arguments.
The problem is that functions like _PyObject_FastCallKeywords() and
_PyObject_FastCallDict() still have to pass a NULL argument for kwargs/kwnames,
and have code to handle keyword arguments.
Attached patch adds _PyObject_FastCall() to reduce the stack consumption. At
the C level, keyword arguments are almost never used. For example,
PyObject_CallFunctionObjArgs() is commonly used, whereas it only uses
positional arguments.
The patch changes also _PyObject_FastCallKeywords() and
_PyObject_FastCallDict() to move the "slow" path creating temporary tuple and
dict in a subfunction which is not inlined. The slow path requires more stack
memory.
Morecall, _PyObject_FastCallKeywords() and _PyObject_FastCallDict() are
modified to call _PyObject_FastCall() if there is no keyword.
The patch might make function calls without keyword arguments faster, I didn't
check.
Stack usage.
$ ./python -c 'import _testcapi, sys; sys.setrecursionlimit(10**5); n=1000;
s=_testcapi.meth_fastcall_stacksize(n); print("%.1f B/call" % (s/n))'
* Reference: 832.8 B/call
* Patch: 656.6 B/call (-176.2 B)
I don't know why the stack usage is not an integer number of bytes?
Combined with the issue #29464 "Specialize FASTCALL for functions with
positional-only parameters", the stack usage can be even more reduced by a few
bytes.
See the issue #28870 for the previous work on reducing stack consumption.
----------
components: Interpreter Core
files: pyobject_fastcall.patch
keywords: patch
messages: 287153
nosy: haypo, inada.naoki, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Add _PyObject_FastCall() to reduce stack consumption
type: resource usage
versions: Python 3.7
Added file: http://bugs.python.org/file46545/pyobject_fastcall.patch
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<http://bugs.python.org/issue29465>
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