Cuni: Tracing JITs in the real world @ CPython Core Dev Sprint

Date:
Thu, 25 Sep 2025 19:13:19 +0000

Description:
Longtime PyPy developer Antonio Cuni has a lengthy
blog post that describes his talk at the recently completed 2025
CPython
Core Dev Sprint , held at Arm in Cambridge, UK. The talk, entitled
"Tracing JIT and real world Python aka: what we can learn from PyPy" was
meant to try to pass on some of his experiences " optimizing existing
code for PyPy at a high-frequency trading firm " to the
developers working on the CPython JIT compiler . His goal was
to raise awareness of some of the problems he encountered: Until now
CPython's performance has been particularly predictable, there are well established "performance tricks" to make code faster, and generally speaking you can mostly reason about the speed of a given piece of code "locally". Adding a JIT completely changes how we reason about performance of a given program, for two reasons: JITted code can be very fast if your code conforms to the heuristics applied by the JIT compiler, but unexpectedly slow(-ish) otherwise; the speed of a given piece of code might depend heavily on what
happens elsewhere in the program, making it much harder to reason about
performance locally. The end result is that modifying a line of code can significantly impact seemingly unrelated code. This effect becomes more pronounced as the JIT becomes more sophisticated. Cuni also gave a talk on Python performance, which LWN covered , at
EuroPython 2025 in July.

======================================================================
Link to news story:
https://lwn.net/Articles/1039612/


--- Mystic BBS v1.12 A49 (Linux/64)
* Origin: tqwNet UK HUB @ hub.uk.erb.pw (1337:1/100)