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gh-116968: Reimplement Tier 2 counters (#117144)

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Introduce a unified 16-bit backoff counter type (``_Py_BackoffCounter``),
shared between the Tier 1 adaptive specializer and the Tier 2 optimizer. The
API used for adaptive specialization counters is changed but the behavior is
(supposed to be) identical.

The behavior of the Tier 2 counters is changed:
- There are no longer dynamic thresholds (we never varied these).
- All counters now use the same exponential backoff.
- The counter for ``JUMP_BACKWARD`` starts counting down from 16.
- The ``temperature`` in side exits starts counting down from 64.
This commit is contained in:
Guido van Rossum 2024-04-04 08:03:27 -07:00 • committed by GitHub
parent 63bbe77d9b
commit 060a96f1a9
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19 changed files with 313 additions and 235 deletions
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Python/specialize.c
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@ -419,22 +419,20 @@ _PyCode_Quicken(PyCodeObject *code)
int caches = _PyOpcode_Caches[opcode];
if (caches) {
// The initial value depends on the opcode
int initial_value;
switch (opcode) {
case JUMP_BACKWARD:
initial_value = 0;
instructions[i + 1].counter = initial_jump_backoff_counter();
break;
case POP_JUMP_IF_FALSE:
case POP_JUMP_IF_TRUE:
case POP_JUMP_IF_NONE:
case POP_JUMP_IF_NOT_NONE:
initial_value = 0x5555; // Alternating 0, 1 bits
instructions[i + 1].cache = 0x5555; // Alternating 0, 1 bits
break;
default:
initial_value = adaptive_counter_warmup();
instructions[i + 1].counter = adaptive_counter_warmup();
break;
}
instructions[i + 1].cache = initial_value;
i += caches;
}
}