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bpo-43760: Speed up check for tracing in interpreter dispatch (#25276)

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* Remove redundant tracing_possible field from interpreter state.

* Move 'use_tracing' from tstate onto C stack, for fastest possible checking in dispatch logic.

* Add comments stressing the importance stack discipline when dealing with CFrames.

* Add NEWS
This commit is contained in:
Mark Shannon 2021-04-13 11:08:14 +01:00 committed by GitHub
parent c2b7a66b91
commit 9e7b2076fb
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GPG key ID: 4AEE18F83AFDEB23
6 changed files with 61 additions and 35 deletions
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22
Include/cpython/pystate.h
View file

@ -29,6 +29,21 @@ typedef int (*Py_tracefunc)(PyObject *, PyFrameObject *, int, PyObject *);
#define PyTrace_OPCODE 7
typedef struct _cframe {
/* This struct will be threaded through the C stack
* allowing fast access to per-thread state that needs
* to be accessed quickly by the interpreter, but can
* be modified outside of the interpreter.
*
* WARNING: This makes data on the C stack accessible from
* heap objects. Care must be taken to maintain stack
* discipline and make sure that instances of this struct cannot
* accessed outside of their lifetime.
*/
int use_tracing;
struct _cframe *previous;
} CFrame;
typedef struct _err_stackitem {
/* This struct represents an entry on the exception stack, which is a
* per-coroutine state. (Coroutine in the computer science sense,
@ -61,7 +76,10 @@ struct _ts {
This is to prevent the actual trace/profile code from being recorded in
the trace/profile. */
int tracing;
int use_tracing;
/* Pointer to current CFrame in the C stack frame of the currently,
* or most recently, executing _PyEval_EvalFrameDefault. */
CFrame *cframe;
Py_tracefunc c_profilefunc;
Py_tracefunc c_tracefunc;
@ -129,6 +147,8 @@ struct _ts {
/* Unique thread state id. */
uint64_t id;
CFrame root_cframe;
/* XXX signal handlers should also be here */
};

6
Include/internal/pycore_interp.h
View file

@ -33,12 +33,6 @@ struct _pending_calls {
struct _ceval_state {
int recursion_limit;
/* Records whether tracing is on for any thread. Counts the number
of threads for which tstate->c_tracefunc is non-NULL, so if the
value is 0, we know we don't have to check this thread's
c_tracefunc. This speeds up the if statement in
_PyEval_EvalFrameDefault() after fast_next_opcode. */
int tracing_possible;
/* This single variable consolidates all requests to break out of
the fast path in the eval loop. */
_Py_atomic_int eval_breaker;

2
Misc/NEWS.d/next/Core and Builtins/2021-04-08-12-20-29.bpo-43760.tBIsD8.rst Normal file
View file

@ -0,0 +1,2 @@
Move the flag for checking whether tracing is enabled to the C stack, from the heap.
Should speed up dispatch in the interpreter.

55
Python/ceval.c
View file

@ -37,6 +37,7 @@ typedef struct {
PyCodeObject *code; // The code object for the bounds. May be NULL.
int instr_prev; // Only valid if code != NULL.
PyCodeAddressRange bounds; // Only valid if code != NULL.
CFrame cframe;
} PyTraceInfo;
@ -1109,8 +1110,6 @@ match_class(PyThreadState *tstate, PyObject *subject, PyObject *type,
static int do_raise(PyThreadState *tstate, PyObject *exc, PyObject *cause);
static int unpack_iterable(PyThreadState *, PyObject *, int, int, PyObject **);
#define _Py_TracingPossible(ceval) ((ceval)->tracing_possible)
PyObject *
PyEval_EvalCode(PyObject *co, PyObject *globals, PyObject *locals)
@ -1307,7 +1306,7 @@ eval_frame_handle_pending(PyThreadState *tstate)
#define DISPATCH() \
{ \
if (_Py_TracingPossible(ceval2) OR_DTRACE_LINE OR_LLTRACE) { \
if (trace_info.cframe.use_tracing OR_DTRACE_LINE OR_LLTRACE) { \
goto tracing_dispatch; \
} \
f->f_lasti = INSTR_OFFSET(); \
@ -1595,8 +1594,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
int oparg; /* Current opcode argument, if any */
PyObject **fastlocals, **freevars;
PyObject *retval = NULL; /* Return value */
struct _ceval_state * const ceval2 = &tstate->interp->ceval;
_Py_atomic_int * const eval_breaker = &ceval2->eval_breaker;
_Py_atomic_int * const eval_breaker = &tstate->interp->ceval.eval_breaker;
PyCodeObject *co;
const _Py_CODEUNIT *first_instr;
@ -1616,11 +1614,20 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
/* Mark trace_info as uninitialized */
trace_info.code = NULL;
/* WARNING: Because the CFrame lives on the C stack,
* but can be accessed from a heap allocated object (tstate)
* strict stack discipline must be maintained.
*/
CFrame *prev_cframe = tstate->cframe;
trace_info.cframe.use_tracing = prev_cframe->use_tracing;
trace_info.cframe.previous = prev_cframe;
tstate->cframe = &trace_info.cframe;
/* push frame */
tstate->frame = f;
co = f->f_code;
if (tstate->use_tracing) {
if (trace_info.cframe.use_tracing) {
if (tstate->c_tracefunc != NULL) {
/* tstate->c_tracefunc, if defined, is a
function that will be called on *every* entry
@ -1782,7 +1789,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
/* line-by-line tracing support */
if (_Py_TracingPossible(ceval2) &&
if (trace_info.cframe.use_tracing &&
tstate->c_tracefunc != NULL && !tstate->tracing) {
int err;
/* see maybe_call_line_trace()
@ -4543,7 +4550,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
PUSH(val);
PUSH(exc);
JUMPTO(handler);
if (_Py_TracingPossible(ceval2)) {
if (trace_info.cframe.use_tracing) {
trace_info.instr_prev = INT_MAX;
}
/* Resume normal execution */
@ -4567,7 +4574,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
f->f_stackdepth = 0;
f->f_state = FRAME_RAISED;
exiting:
if (tstate->use_tracing) {
if (trace_info.cframe.use_tracing) {
if (tstate->c_tracefunc) {
if (call_trace_protected(tstate->c_tracefunc, tstate->c_traceobj,
tstate, f, &trace_info, PyTrace_RETURN, retval)) {
@ -4584,6 +4591,10 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
/* pop frame */
exit_eval_frame:
/* Restore previous cframe */
tstate->cframe = trace_info.cframe.previous;
tstate->cframe->use_tracing = trace_info.cframe.use_tracing;
if (PyDTrace_FUNCTION_RETURN_ENABLED())
dtrace_function_return(f);
_Py_LeaveRecursiveCall(tstate);
@ -5507,7 +5518,7 @@ call_trace(Py_tracefunc func, PyObject *obj,
if (tstate->tracing)
return 0;
tstate->tracing++;
tstate->use_tracing = 0;
tstate->cframe->use_tracing = 0;
if (frame->f_lasti < 0) {
frame->f_lineno = frame->f_code->co_firstlineno;
}
@ -5517,7 +5528,7 @@ call_trace(Py_tracefunc func, PyObject *obj,
}
result = func(obj, frame, what, arg);
frame->f_lineno = 0;
tstate->use_tracing = ((tstate->c_tracefunc != NULL)
tstate->cframe->use_tracing = ((tstate->c_tracefunc != NULL)
|| (tstate->c_profilefunc != NULL));
tstate->tracing--;
return result;
@ -5528,15 +5539,15 @@ _PyEval_CallTracing(PyObject *func, PyObject *args)
{
PyThreadState *tstate = _PyThreadState_GET();
int save_tracing = tstate->tracing;
int save_use_tracing = tstate->use_tracing;
int save_use_tracing = tstate->cframe->use_tracing;
PyObject *result;
tstate->tracing = 0;
tstate->use_tracing = ((tstate->c_tracefunc != NULL)
tstate->cframe->use_tracing = ((tstate->c_tracefunc != NULL)
|| (tstate->c_profilefunc != NULL));
result = PyObject_Call(func, args, NULL);
tstate->tracing = save_tracing;
tstate->use_tracing = save_use_tracing;
tstate->cframe->use_tracing = save_use_tracing;
return result;
}
@ -5590,7 +5601,7 @@ _PyEval_SetProfile(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
tstate->c_profilefunc = NULL;
tstate->c_profileobj = NULL;
/* Must make sure that tracing is not ignored if 'profileobj' is freed */
tstate->use_tracing = tstate->c_tracefunc != NULL;
tstate->cframe->use_tracing = tstate->c_tracefunc != NULL;
Py_XDECREF(profileobj);
Py_XINCREF(arg);
@ -5598,7 +5609,7 @@ _PyEval_SetProfile(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
tstate->c_profilefunc = func;
/* Flag that tracing or profiling is turned on */
tstate->use_tracing = (func != NULL) || (tstate->c_tracefunc != NULL);
tstate->cframe->use_tracing = (func != NULL) || (tstate->c_tracefunc != NULL);
return 0;
}
@ -5626,14 +5637,12 @@ _PyEval_SetTrace(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
return -1;
}
struct _ceval_state *ceval2 = &tstate->interp->ceval;
PyObject *traceobj = tstate->c_traceobj;
ceval2->tracing_possible += (func != NULL) - (tstate->c_tracefunc != NULL);
tstate->c_tracefunc = NULL;
tstate->c_traceobj = NULL;
/* Must make sure that profiling is not ignored if 'traceobj' is freed */
tstate->use_tracing = (tstate->c_profilefunc != NULL);
tstate->cframe->use_tracing = (tstate->c_profilefunc != NULL);
Py_XDECREF(traceobj);
Py_XINCREF(arg);
@ -5641,7 +5650,7 @@ _PyEval_SetTrace(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
tstate->c_tracefunc = func;
/* Flag that tracing or profiling is turned on */
tstate->use_tracing = ((func != NULL)
tstate->cframe->use_tracing = ((func != NULL)
|| (tstate->c_profilefunc != NULL));
return 0;
@ -5836,7 +5845,7 @@ PyEval_GetFuncDesc(PyObject *func)
}
#define C_TRACE(x, call) \
if (tstate->use_tracing && tstate->c_profilefunc) { \
if (trace_info->cframe.use_tracing && tstate->c_profilefunc) { \
if (call_trace(tstate->c_profilefunc, tstate->c_profileobj, \
tstate, tstate->frame, trace_info, \
PyTrace_C_CALL, func)) { \
@ -5917,7 +5926,7 @@ call_function(PyThreadState *tstate,
Py_ssize_t nargs = oparg - nkwargs;
PyObject **stack = (*pp_stack) - nargs - nkwargs;
if (tstate->use_tracing) {
if (trace_info->cframe.use_tracing) {
x = trace_call_function(tstate, trace_info, func, stack, nargs, kwnames);
}
else {
@ -5950,7 +5959,7 @@ do_call_core(PyThreadState *tstate,
}
else if (Py_IS_TYPE(func, &PyMethodDescr_Type)) {
Py_ssize_t nargs = PyTuple_GET_SIZE(callargs);
if (nargs > 0 && tstate->use_tracing) {
if (nargs > 0 && trace_info->cframe.use_tracing) {
/* We need to create a temporary bound method as argument
for profiling.

3
Python/pystate.c
View file

@ -624,7 +624,8 @@ new_threadstate(PyInterpreterState *interp, int init)
tstate->recursion_headroom = 0;
tstate->stackcheck_counter = 0;
tstate->tracing = 0;
tstate->use_tracing = 0;
tstate->root_cframe.use_tracing = 0;
tstate->cframe = &tstate->root_cframe;
tstate->gilstate_counter = 0;
tstate->async_exc = NULL;
tstate->thread_id = PyThread_get_thread_ident();

8
Python/sysmodule.c
View file

@ -252,7 +252,7 @@ sys_audit_tstate(PyThreadState *ts, const char *event,
/* Disallow tracing in hooks unless explicitly enabled */
ts->tracing++;
ts->use_tracing = 0;
ts->cframe->use_tracing = 0;
while ((hook = PyIter_Next(hooks)) != NULL) {
_Py_IDENTIFIER(__cantrace__);
PyObject *o;
@ -265,14 +265,14 @@ sys_audit_tstate(PyThreadState *ts, const char *event,
break;
}
if (canTrace) {
ts->use_tracing = (ts->c_tracefunc || ts->c_profilefunc);
ts->cframe->use_tracing = (ts->c_tracefunc || ts->c_profilefunc);
ts->tracing--;
}
PyObject* args[2] = {eventName, eventArgs};
o = _PyObject_FastCallTstate(ts, hook, args, 2);
if (canTrace) {
ts->tracing++;
ts->use_tracing = 0;
ts->cframe->use_tracing = 0;
}
if (!o) {
break;
@ -280,7 +280,7 @@ sys_audit_tstate(PyThreadState *ts, const char *event,
Py_DECREF(o);
Py_CLEAR(hook);
}
ts->use_tracing = (ts->c_tracefunc || ts->c_profilefunc);
ts->cframe->use_tracing = (ts->c_tracefunc || ts->c_profilefunc);
ts->tracing--;
if (_PyErr_Occurred(ts)) {
goto exit;