 CPython JIT

ID: cpython-jit

To enable tested on Ubuntu 25.04:

git clone https://github.com/python/cpython
cd cpython
git checkout v3.13.7
./configure --enable-experimental-jit
make -j

However, the JIT appears to be useless tested as of this Python version, lol:

time ./python python/inc_loop.py 10000000

but the result is just as pathetic as without JIT currently, taking about 1 second for only 10m loops.

This can be compared with the optimal assembly from c/inc_loop_asm.c:

time ./inc_loop_asm.out 1000000000

which does 1 billion loops in about half a second on P14s.

For comparison, PyPy actually speeds things up and does 1 billion loops in about a second, so only 2x worse than native.

TODO triple check that JIT is enabled. Many threads say the command is:

./python -c 'import sysconfig; sysconfig.get_config_var("JIT_DEPS")'

but that fails with:

ModuleNotFoundError: No module named '_sysconfigdata__linux_x86_64-linux-gnu'

For comparison with a properly implemented dynamic language JIT running nodejs/inc_loop.js does 1 billion loops in 0.6s on v22.14.0, close to native.

tonybaloney.github.io/posts/python-gets-a-jit.html documents what the initial "JIT" implementation does. It is just an extremely naive concatenation of instructions that avoids a for + switch. No wonder it doesn't speed things up much at all.

 New to topics? Read the docs here!