Reflections on 2 years of CPython's JIT Compiler: The good, the bad, the ugly

10 months ago

The CPython JIT is still experimental and not ready for prime time.
The JIT was initially a solo effort but has grown into a community-driven project.
Efforts have been made to make the JIT easier to work on and teach, including using a tracing JIT for easier static analysis.
CPython 3.13's JIT is often slower than the interpreter, especially when built with modern compilers like Clang 20.
Performance improvements in CPython 3.14's JIT are mixed, with some benchmarks showing speedups and others showing slowdowns.
Media coverage has sometimes misrepresented the JIT's performance, leading to incorrect expectations.
Despite current performance issues, there is optimism for future improvements due to a growing community and ongoing optimization efforts.
The author acknowledges personal shortcomings in contributing to the JIT's development and clarifies points about performance metrics.

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