[issue28870] Reduce stack consumption of PyObject_CallFunctionObjArgs() and like

[STINNER Victor]

STINNER Victor added the comment:

Impact of the _PY_FASTCALL_SMALL_STACK constant:

* _PY_FASTCALL_SMALL_STACK=1: 528 bytes/call

test_python_call 7376
test_python_getitem 6544
test_python_iterator 5572
=> total: 19 492

* _PY_FASTCALL_SMALL_STACK=3: 528 bytes/call

test_python_call 7272
test_python_getitem 6464
test_python_iterator 5512
=> total: 19 248

* _PY_FASTCALL_SMALL_STACK=5 (current value): 560 bytes/call

test_python_call 7172
test_python_getitem 6232
test_python_iterator 5344
=> total: 19 636

* _PY_FASTCALL_SMALL_STACK=10: 592 bytes/call

test_python_call 6984
test_python_getitem 5952
test_python_iterator 5132
=> total: 18 068

Increasing _PY_FASTCALL_SMALL_STACK has a clear effect on the total. Total decreases when _PY_FASTCALL_SMALL_STACK increases.


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no_small_stack.patch with _PY_FASTCALL_SMALL_STACK=3: 368 bytes/call

test_python_call 7272
test_python_getitem 6628
test_python_iterator 5632
=> total: 19 532

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<http://bugs.python.org/issue28870>
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