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GH-93354: Use exponential backoff to avoid excessive specialization attempts. #93355

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merged 2 commits into from
May 31, 2022
Merged

GH-93354: Use exponential backoff to avoid excessive specialization attempts. #93355

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530fa9b
Use exponential backoff to avoid excessive specialization attempts.
markshannon May 30, 2022
89acc3e
Add comment explaining counters and exponential backoff.
markshannon May 30, 2022
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32 changes: 30 additions & 2 deletions Include/internal/pycore_code.h
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Original file line number Diff line number Diff line change
Expand Up @@ -227,8 +227,10 @@ extern void _PyLineTable_InitAddressRange(
extern int _PyLineTable_NextAddressRange(PyCodeAddressRange *range);
extern int _PyLineTable_PreviousAddressRange(PyCodeAddressRange *range);


#define ADAPTIVE_CACHE_BACKOFF 64
/* With a 16 counter, we have 12 bits for the counter value, and 4 bits for the backoff */
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#define ADAPTIVE_BACKOFF_BITS 4
/* The initial counter value is backoff**2-1, so a backoff of 5 gives a value of 31 */
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#define ADAPTIVE_BACKOFF_START 5

/* Specialization functions */

Expand Down Expand Up @@ -423,6 +425,32 @@ write_location_entry_start(uint8_t *ptr, int code, int length)
}


static inline uint16_t
adaptive_counter_bits(int value, int backoff) {
return (value << ADAPTIVE_BACKOFF_BITS) |
(backoff & ((1<<ADAPTIVE_BACKOFF_BITS)-1));
}

#define MAX_BACKOFF_VALUE (16 - ADAPTIVE_BACKOFF_BITS)

static inline uint16_t
adaptive_counter_start(void) {
unsigned int value = (1 << ADAPTIVE_BACKOFF_START) - 1;
return adaptive_counter_bits(value, ADAPTIVE_BACKOFF_START);
}

static inline uint16_t
adaptive_counter_backoff(uint16_t counter) {
unsigned int backoff = counter & ((1<<ADAPTIVE_BACKOFF_BITS)-1);
backoff++;
if (backoff > MAX_BACKOFF_VALUE) {
backoff = MAX_BACKOFF_VALUE;
}
unsigned int value = (1 << backoff) - 1;
return adaptive_counter_bits(value, backoff);
}


#ifdef __cplusplus
}
#endif
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2022-05-30-15-35-42.gh-issue-93354.RZk8gs.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Use exponential backoff for specialization counters in the interpreter. Can
reduce the number of failed specializations significantly and avoid slowdown
for those parts of a program that are not suitable for specialization.
46 changes: 25 additions & 21 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1561,7 +1561,11 @@ eval_frame_handle_pending(PyThreadState *tstate)
dtrace_function_entry(frame); \
}

#define ADAPTIVE_COUNTER_IS_ZERO(cache) \
(cache)->counter < (1<<ADAPTIVE_BACKOFF_BITS)

#define DECREMENT_ADAPTIVE_COUNTER(cache) \
(cache)->counter -= (1<<ADAPTIVE_BACKOFF_BITS)

static int
trace_function_entry(PyThreadState *tstate, _PyInterpreterFrame *frame)
Expand Down Expand Up @@ -2156,7 +2160,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int

TARGET(BINARY_SUBSCR_ADAPTIVE) {
_PyBinarySubscrCache *cache = (_PyBinarySubscrCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *sub = TOP();
PyObject *container = SECOND();
next_instr--;
Expand All @@ -2167,7 +2171,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(BINARY_SUBSCR, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(BINARY_SUBSCR);
}
}
Expand Down Expand Up @@ -2321,7 +2325,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int

TARGET(STORE_SUBSCR_ADAPTIVE) {
_PyStoreSubscrCache *cache = (_PyStoreSubscrCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *sub = TOP();
PyObject *container = SECOND();
next_instr--;
Expand All @@ -2332,7 +2336,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(STORE_SUBSCR, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(STORE_SUBSCR);
}
}
Expand Down Expand Up @@ -2815,15 +2819,15 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
TARGET(UNPACK_SEQUENCE_ADAPTIVE) {
assert(cframe.use_tracing == 0);
_PyUnpackSequenceCache *cache = (_PyUnpackSequenceCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *seq = TOP();
next_instr--;
_Py_Specialize_UnpackSequence(seq, next_instr, oparg);
NOTRACE_DISPATCH_SAME_OPARG();
}
else {
STAT_INC(UNPACK_SEQUENCE, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(UNPACK_SEQUENCE);
}
}
Expand Down Expand Up @@ -3056,7 +3060,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
TARGET(LOAD_GLOBAL_ADAPTIVE) {
assert(cframe.use_tracing == 0);
_PyLoadGlobalCache *cache = (_PyLoadGlobalCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *name = GETITEM(names, oparg>>1);
next_instr--;
if (_Py_Specialize_LoadGlobal(GLOBALS(), BUILTINS(), next_instr, name) < 0) {
Expand All @@ -3066,7 +3070,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(LOAD_GLOBAL, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(LOAD_GLOBAL);
}
}
Expand Down Expand Up @@ -3480,7 +3484,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
TARGET(LOAD_ATTR_ADAPTIVE) {
assert(cframe.use_tracing == 0);
_PyAttrCache *cache = (_PyAttrCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *owner = TOP();
PyObject *name = GETITEM(names, oparg);
next_instr--;
Expand All @@ -3491,7 +3495,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(LOAD_ATTR, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(LOAD_ATTR);
}
}
Expand Down Expand Up @@ -3589,7 +3593,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
TARGET(STORE_ATTR_ADAPTIVE) {
assert(cframe.use_tracing == 0);
_PyAttrCache *cache = (_PyAttrCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *owner = TOP();
PyObject *name = GETITEM(names, oparg);
next_instr--;
Expand All @@ -3600,7 +3604,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(STORE_ATTR, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(STORE_ATTR);
}
}
Expand Down Expand Up @@ -3719,7 +3723,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
TARGET(COMPARE_OP_ADAPTIVE) {
assert(cframe.use_tracing == 0);
_PyCompareOpCache *cache = (_PyCompareOpCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *right = TOP();
PyObject *left = SECOND();
next_instr--;
Expand All @@ -3728,7 +3732,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(COMPARE_OP, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(COMPARE_OP);
}
}
Expand Down Expand Up @@ -4526,7 +4530,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
TARGET(LOAD_METHOD_ADAPTIVE) {
assert(cframe.use_tracing == 0);
_PyLoadMethodCache *cache = (_PyLoadMethodCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *owner = TOP();
PyObject *name = GETITEM(names, oparg);
next_instr--;
Expand All @@ -4537,7 +4541,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(LOAD_METHOD, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(LOAD_METHOD);
}
}
Expand Down Expand Up @@ -4775,7 +4779,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int

TARGET(CALL_ADAPTIVE) {
_PyCallCache *cache = (_PyCallCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
next_instr--;
int is_meth = is_method(stack_pointer, oparg);
int nargs = oparg + is_meth;
Expand All @@ -4789,7 +4793,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(CALL, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
goto call_function;
}
}
Expand Down Expand Up @@ -5521,7 +5525,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
TARGET(BINARY_OP_ADAPTIVE) {
assert(cframe.use_tracing == 0);
_PyBinaryOpCache *cache = (_PyBinaryOpCache *)next_instr;
if (cache->counter == 0) {
if (ADAPTIVE_COUNTER_IS_ZERO(cache)) {
PyObject *lhs = SECOND();
PyObject *rhs = TOP();
next_instr--;
Expand All @@ -5530,7 +5534,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
else {
STAT_INC(BINARY_OP, deferred);
cache->counter--;
DECREMENT_ADAPTIVE_COUNTER(cache);
JUMP_TO_INSTRUCTION(BINARY_OP);
}
}
Expand Down Expand Up @@ -5658,7 +5662,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
assert(adaptive_opcode);
_Py_SET_OPCODE(next_instr[-1], adaptive_opcode);
STAT_INC(opcode, deopt);
*counter = ADAPTIVE_CACHE_BACKOFF;
*counter = adaptive_counter_start();
}
next_instr--;
DISPATCH_GOTO();
Expand Down
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