gh-141504: Factor out tracing and optimization heuristics into a single object by corona10 · Pull Request #143381 · python/cpython · GitHub

Issue: Factor out tracing and optimization heuristics into a single "policy" object. #141504

We may need to extract utility function to handle those things.

Can you rename this to _PyJitPolicy pleases?

Also please then wrap this into an overall struct called _PyPolicies. The reason is that we might want to add more structs later, like for the interpreter.

So it should be

Suggested change

      
            typedef struct _PyJitMetrics {
          
                uint16_t jump_backward_initial_value;
          
                uint16_t jump_backward_initial_backoff;
          
                uint16_t side_exit_initial_value;
          
                uint16_t side_exit_initial_backoff;
          
            } _PyJitMetrics;
          
            typedef struct _PyJitPolicy {
          
                uint16_t jump_backward_initial_value;
          
                uint16_t jump_backward_initial_backoff;
          
                uint16_t side_exit_initial_value;
          
                uint16_t side_exit_initial_backoff;
          
            } _PyJitPolicy;
          
            typedef struct _PyPolicy {
          
                _PyJitPolicy jit;
          
            } _PyPolicy;

@Fidget-Spinner
The crash is directly related to this line.
But ENABLE_SPECIALIZATION_FT does not mean TIER2 is enabled.

Do we need to move jump_backward_initial_value and jump_backward_initial_backoff to policy.interpreter?

JUMP_BACKWARD_INITIAL_VALUE is only used by the JIT. On normal build/FT build, the CACHE of JUMP_BACKWARD is unused. So we can just keep it for the JIT.

Hmm I realised the CI is now failing because FT doesn't build with JIT.

In that case, yes please move this to an interpreter policy.

This needs to be moved out of the ifdef. CI is failing.

Some comments to cleanup the code. After this I will approve. Thanks!

This should take a single value _tstate/tstate and grab the jump backward values from it.

Same here.

Rename to init_policy

rename here as well

Great. Thanks!

Note: the names are a little lengthy. But considering this is an internal CPython only env var used for testing, we can determine proper names later when/if we decide to expose them.

I have some questions.

Why set thresholds per thread, rather than per interpreter. Why would we want per-thread values?
Why set and store the threshold and backoff separately rather than as a single backoff counter?

I've added a new comment on the issue, that will hopefully clarify what I was after.

…a single object (pythongh-143381)

corona10 added 3 commits January 3, 2026 15:30

pythongh-141504 : Configurable JIT optimization thresholds

0ebb67a

Add NEWS.d

2b1cbbc

nit

7fce731

corona10 requested review from Fidget-Spinner, ZeroIntensity, ericsnowcurrently and markshannon as code owners January 3, 2026 07:02

bedevere-app Bot added the awaiting core review label Jan 3, 2026

bedevere-app Bot mentioned this pull request Jan 3, 2026

Factor out tracing and optimization heuristics into a single "policy" object. #141504

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corona10 changed the title gh-141504: Factor out tracing and optimization heuristics into a single object [WIP] gh-141504: Factor out tracing and optimization heuristics into a single object Jan 3, 2026

corona10 marked this pull request as draft January 3, 2026 07:23

bedevere-app Bot removed the awaiting core review label Jan 3, 2026

corona10 commented Jan 3, 2026

View reviewed changes

fix

d01f572

corona10 changed the title [WIP] gh-141504: Factor out tracing and optimization heuristics into a single object gh-141504: Factor out tracing and optimization heuristics into a single object Jan 3, 2026

nit

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corona10 marked this pull request as ready for review January 3, 2026 07:59

bedevere-app Bot added the awaiting core review label Jan 3, 2026

Fidget-Spinner reviewed Jan 3, 2026

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corona10 added 2 commits January 3, 2026 20:55

Address code review

a0e6965

nit

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corona10 commented Jan 3, 2026

View reviewed changes

Address code review

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corona10 requested a review from Fidget-Spinner January 3, 2026 13:38

Fidget-Spinner reviewed Jan 3, 2026

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fix

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corona10 requested a review from Fidget-Spinner January 3, 2026 14:22

Fidget-Spinner reviewed Jan 3, 2026

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corona10 added 2 commits January 3, 2026 23:49

Address code review

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nit

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Fidget-Spinner approved these changes Jan 3, 2026

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bedevere-app Bot removed the awaiting core review label Jan 3, 2026

fix

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bedevere-app Bot added the awaiting merge label Jan 3, 2026

corona10 added 2 commits January 3, 2026 23:54

nit

fe0d38a

nit

304c70c

corona10 enabled auto-merge (squash) January 3, 2026 14:56

nit

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corona10 disabled auto-merge January 3, 2026 14:58

corona10 enabled auto-merge (squash) January 3, 2026 14:58

corona10 merged commit 12283f6 into python:main Jan 3, 2026
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bedevere-app Bot removed the awaiting merge label Jan 3, 2026

thunder-coding pushed a commit to thunder-coding/cpython that referenced this pull request Feb 15, 2026

pythongh-141504 : Factor out tracing and optimization heuristics into …

8ede7a5

…a single object (pythongh-143381)

+                      PyThreadState *tstate = _PyThreadState_GET();
+                      _PyThreadStateImpl *tstate_impl = (_PyThreadStateImpl *)tstate;
+                      jump_counter = initial_jump_backoff_counter(
+                          tstate_impl->policy.jit.jump_backward_initial_value,

               #endif
               #if _Py_TIER2
                   _PyJitTracerState jit_tracer_state;
+                  _PyPolicy policy;

               #define JUMP_BACKWARD_INITIAL_BACKOFF 6
               static inline _Py_BackoffCounter
-              initial_jump_backoff_counter(void)
+              initial_jump_backoff_counter(uint16_t initial_value, uint16_t initial_backoff)

+                  _tstate->jit_metrics.side_exit_initial_value = SIDE_EXIT_INITIAL_VALUE;
+                  _tstate->jit_metrics.side_exit_initial_backoff = SIDE_EXIT_INITIAL_BACKOFF;
+                  char *env = Py_GETENV("PYTHON_JIT_JUMP_BACKWARD_INITIAL_VALUE");

               static inline _Py_BackoffCounter
-              initial_temperature_backoff_counter(void)
+              initial_temperature_backoff_counter(uint16_t initial_value, uint16_t initial_backoff)

               }
+              static inline void
+              init_jit_metric(uint16_t *target, const char *env_name, uint16_t default_value,

                   _tstate->asyncio_running_task = NULL;
+                  // Initialize interpreter policy from environment variables
+                  init_jit_metric(&_tstate->policy.interp.jump_backward_initial_value,

gh-141504: Factor out tracing and optimization heuristics into a single object by corona10 · Pull Request #143381 · python/cpython · GitHub

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gh-141504: Factor out tracing and optimization heuristics into a single object - #143381

gh-141504: Factor out tracing and optimization heuristics into a single object#143381corona10 merged 15 commits intopython:mainpython/cpython:mainfrom corona10:gh-141504corona10/cpython:gh-141504Copy head branch name to clipboard

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gh-141504: Factor out tracing and optimization heuristics into a single object#143381
corona10 merged 15 commits into
python:mainfrom
corona10:gh-141504

corona10 commented Jan 3, 2026 •
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