PEP 744: JIT Compilation

[brandtbucher]

(Sorry for the late reply.)

@vstinner

Would it be possible to have a a way to configure Python to disable the JIT by default, but have a command line options (ex: env var and/or CLI option) to enable it? The use case is to ship a single binary in Fedora with JIT disabled, to avoid any issues with the JIT by default, but let early adopters to play with it.

Example:

• python3.13 runs Python without the JIT (disabled)
• python3.13 -X jit runs Python with the JIT enabled

Fedora discussion: Handling --enable-experimental-jit in Python 3.13 - python-devel - Fedora Mailing-Lists

So I’ve talked this over with the rest of the Faster CPython team, and we think the following scheme would make sense for 3.13 (names subject to bikeshedding):

• --enable-experimental-jit=no (the default): Do not build the JIT or the micro-op interpreter. The new PYTHON_JIT environment variable has no effect.

• --enable-experimental-jit=interpreter: Do not build the JIT, but do build and enable the micro-op interpreter. This is useful for those of us who find ourselves developing or debugging micro-ops (but don’t want to deal with the JIT), and is equivalent to using the -X uops or PYTHON_UOPS=1 options today. PYTHON_JIT=0 can be used to disable the micro-op interpreter at runtime.

• --enable-experimental-jit=yes-off: Build the JIT, but do not enable it by default. PYTHON_JIT=1 can be used to enable it at runtime.

• --enable-experimental-jit=yes (or just --enable-experimental-jit): Build the JIT and enable it by default. PYTHON_JIT=0 can be used to disable it at runtime.

I think this is sufficiently flexible that it covers the most common use-cases… for example, @markshannon can build with --enable-experimental-jit=interpreter, Fedora can build with --enable-experimental-jit=yes-off, and I can build with --enable-experimental-jit. And if it isn’t flexible enough, we can always add more configurations later.