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GeezerVison is showing github.com — gh-161676: Reduce perf trampoline overhead by pablogsal · Pull Request #161677 · python/cpython

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@pablogsal

@pablogsal pablogsal commented Nov 9, 2026 •
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Two changes to reduce the -X perf overhead:

  1. Move the co_extra lookup out of py_trampoline_evaluator so it tail-calls the trampoline instead of keeping an extra native frame per call.
  2. Keep specialized calls and generator resumes when the PEP 523 hook is the perf trampoline. _PUSH_FRAME enters the frame through the hook, so perf still sees every Python frame.

Slowdown with -X perf relative to main without it (PGO + ThinLTO, Clang 21):

Benchmark main This PR
generators +234% +105%
generator_resumes +72% +62%
python_calls +50% +30%
scimark_lu +42% +35%
base32_small +11% +5%
json_loads +1% +2%
geometric mean (above) +55% +36%
pyperformance geomean (121) +11.9% +8.1%

No measurable change without -X perf.

  • Issue: Reduce perf trampoline overhead #161676

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@bedevere-app bedevere-app Bot mentioned this pull request Nov 9, 2026
Reduce perf trampoline overhead #161676
Open
@bedevere-app bedevere-app Bot added the type-feature A feature request or enhancement label Nov 9, 2026
@pablogsal pablogsal added the performance Performance or resource usage label Nov 9, 2026 — with ChatGPT Codex Connector
@pablogsal
pythongh-161676: Let the perf trampoline evaluator tail-call the tram…
bd91c37 
…poline
@pablogsal
pablogsal force-pushed the perf-trampoline-specialized-calls branch from 5afac8d to bd91c37 Compare November 9, 2026 17:49
@pablogsal pablogsal changed the title gh-161676: Reduce perf trampoline overhead gh-161676: Let the perf trampoline evaluator tail-call the trampoline Nov 9, 2026
pablogsal added 2 commits November 9, 2026 17:50
@pablogsal
Fix continuation line alignment
dc00633
@pablogsal
pythongh-161676: Keep specialized calls enabled under the perf trampo…
88c2e1b 
…line
@pablogsal pablogsal changed the title gh-161676: Let the perf trampoline evaluator tail-call the trampoline gh-161676: Reduce perf trampoline overhead Nov 9, 2026
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@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently will be requested when the pull request is marked ready for review ericsnowcurrently is a code owner
@ZeroIntensity ZeroIntensity Awaiting requested review from ZeroIntensity ZeroIntensity will be requested when the pull request is marked ready for review ZeroIntensity is a code owner
@FFY00 FFY00 Awaiting requested review from FFY00 FFY00 will be requested when the pull request is marked ready for review FFY00 is a code owner
@markshannon markshannon Awaiting requested review from markshannon markshannon will be requested when the pull request is marked ready for review markshannon is a code owner

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@pablogsal
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