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changeset: 105047:59b91b4e9506 user: Victor Stinner victor.stinner@gmail.com date: Fri Nov 11 02:13:35 2016 +0100 files: Include/pyport.h Objects/frameobject.c Python/ceval.c Python/errors.c description: Issue #28618: Make hot functions using __attribute__((hot)) When Python is not compiled with PGO, the performance of Python on call_simple and call_method microbenchmarks depend highly on the code placement. In the worst case, the performance slowdown can be up to 70%. The GCC __attribute__((hot)) attribute helps to keep hot code close to reduce the risk of such major slowdown. This attribute is ignored when Python is compiled with PGO. The following functions are considered as hot according to statistics collected by perf record/perf report: * _PyEval_EvalFrameDefault() * call_function() * _PyFunction_FastCall() * PyFrame_New() * frame_dealloc() * PyErr_Occurred() diff -r c2c72616c9f1 -r 59b91b4e9506 Include/pyport.h --- a/Include/pyport.h Fri Nov 11 01:43:56 2016 +0100 +++ b/Include/pyport.h Fri Nov 11 02:13:35 2016 +0100 @@ -490,13 +490,36 @@ * typedef int T1 Py_DEPRECATED(2.4); * extern int x() Py_DEPRECATED(2.5); */ -#if defined(__GNUC__) && ((__GNUC__ >= 4) || \ - (__GNUC__ == 3) && (__GNUC_MINOR__ >= 1)) +#if defined(__GNUC__) \ + && ((__GNUC__ >= 4) || (__GNUC__ == 3) && (__GNUC_MINOR__ >= 1)) #define Py_DEPRECATED(VERSION_UNUSED) __attribute__((__deprecated__)) #else #define Py_DEPRECATED(VERSION_UNUSED) #endif + +/* Py_HOT_FUNCTION + * The hot attribute on a function is used to inform the compiler that the + * function is a hot spot of the compiled program. The function is optimized + * more aggressively and on many target it is placed into special subsection of + * the text section so all hot functions appears close together improving + * locality. + * + * Usage: + * int Py_HOT_FUNCTION x() { return 3; } + * + * Issue #28618: This attribute must not be abused, otherwise it can have a + * negative effect on performance. Only the functions were Python spend most of + * its time must use it. Use a profiler when running performance benchmark + * suite to find these functions. + */ +#if defined(__GNUC__) \ + && ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 3)) +#define _Py_HOT_FUNCTION __attribute__((hot)) +#else +#define _Py_HOT_FUNCTION +#endif + /************************************************************************** Prototypes that are missing from the standard include files on some systems (and possibly only some versions of such systems.) diff -r c2c72616c9f1 -r 59b91b4e9506 Objects/frameobject.c --- a/Objects/frameobject.c Fri Nov 11 01:43:56 2016 +0100 +++ b/Objects/frameobject.c Fri Nov 11 02:13:35 2016 +0100 @@ -409,7 +409,7 @@ /* max value for numfree */ #define PyFrame_MAXFREELIST 200 -static void +static void _Py_HOT_FUNCTION frame_dealloc(PyFrameObject *f) { PyObject **p, **valuestack; @@ -605,7 +605,7 @@ return 1; } -PyFrameObject * +PyFrameObject* _Py_HOT_FUNCTION PyFrame_New(PyThreadState *tstate, PyCodeObject *code, PyObject *globals, PyObject *locals) { diff -r c2c72616c9f1 -r 59b91b4e9506 Python/ceval.c --- a/Python/ceval.c Fri Nov 11 01:43:56 2016 +0100 +++ b/Python/ceval.c Fri Nov 11 02:13:35 2016 +0100 @@ -718,7 +718,7 @@ return tstate->interp->eval_frame(f, throwflag); } -PyObject * +PyObject* _Py_HOT_FUNCTION _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag) { #ifdef DXPAIRS @@ -4771,7 +4771,7 @@ x = call; \ } -static PyObject * +static PyObject* _Py_HOT_FUNCTION call_function(PyObject ***pp_stack, Py_ssize_t oparg, PyObject *kwnames) { PyObject **pfunc = (*pp_stack) - oparg - 1; @@ -4844,7 +4844,7 @@ done before evaluating the frame. */ -static PyObject* +static PyObject* _Py_HOT_FUNCTION _PyFunction_FastCall(PyCodeObject *co, PyObject **args, Py_ssize_t nargs, PyObject *globals) { diff -r c2c72616c9f1 -r 59b91b4e9506 Python/errors.c --- a/Python/errors.c Fri Nov 11 01:43:56 2016 +0100 +++ b/Python/errors.c Fri Nov 11 02:13:35 2016 +0100 @@ -158,7 +158,7 @@ } -PyObject * +PyObject* _Py_HOT_FUNCTION PyErr_Occurred(void) { PyThreadState *tstate = PyThreadState_GET(); /victor.stinner@gmail.com