New submission from STINNER Victor: A new FASTCALL calling convention was added to Python 3.6. It allows to avoid the creation of a temporary tuple to pass positional arguments and a temporary dictionary to pass keyword arguments. A new METH_FASTCALL calling convention was added for C functions. Most functions now support fastcall, except objects with a __call__() method which have to go through slot_tp_call() which still requires a tuple and dictionary.
I tried multiple implementations to support fast calls to call the __call__() method, but I had practical and technical issues. First, I tried to reuse the tp_call field to PyTypeObject: it can be a regular call (tuple/dict for arguments) or a fast call. I added a flag to the tp_flags field. It was tricky to support class inheritance, decide to set or clear the flag. But the real blocker issue is fAthat it is obviously breaks the backward compatibility: existing code calling directly tp_call with the regular calling convention will crash immediatly, and the error is not catched during compilation, even if the code is recompiled. I propose a different design: add a new tp_fastcall field to PyTypeObject and use a wrapper for tp_call when tp_fastcall is defined. If a type defines tp_fastcall but not, the tp_call wrapper "simply" calls tp_fastcall. Advantages: * The wrapper is trivial * Minor changes to PyType_Ready() to support inheritance (simple logic) * Fully backward compatible * If tp_call is called directly without keyword arguments, there is no overhead but a speedup! Inheritance: * If a type only defines tp_call, tp_fastcall is not inherited from the parent: tp_fastcall is set to NULL. * If a type only defines tp_fastcall: tp_fastcall is always use (tp_call uses the wrapper) * If a type defines tp_call and tp_fastcall, PyObject_Call() uses tp_call whereas _PyObject_FastCallDict() uses tp_fastcall. Functions of the C API will be modified to use tp_fastcall if available. The plan is then to patch most Python types to replace their tp_call with tp_fastcall. First, most important (common) types like Python and C functions, descriptors, and the various kinds of wrappers should be patched. Later, we should maybe discuss on a case by case basis to decide if it's worth it. I will try to run benchmark before any kind. ---------- messages: 285388 nosy: haypo, inada.naoki, serhiy.storchaka priority: normal pull_requests: 17 severity: normal status: open title: Add tp_fastcall to PyTypeObject: support FASTCALL calling convention for all callable objects type: performance versions: Python 3.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue29259> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
