Reduce overhead of bindings requiring cuPythonInit()

[mdboom]

Description

This reduces the calling overhead of binding functions that require cuPythonInit or cudaPythonInit to be called.

This reduces the time it takes to call driver.cuDeviceGet(0) (for example) by about 50ns (on my machine):

• Base: Mean +- std dev: 149 ns +- 8 ns
• This PR: Mean +- std dev: 101 ns +- 2 ns

Note that these times include the work done by the actual underlying cuDeviceGet call, not just the function call overhead.

Why this works

The cuPythonInit function is extremely large, so no C compiler is likely to ever inline it. By creating a small wrapper function just to check the init flag and then delegate to the big function, the C compiler inlines it. This not only removes a C function call, but probably helps out the branch predictor when checking the flag.

closes

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[Copilot]

Pull Request Overview

This PR optimizes the initialization check for CUDA Python bindings by reducing function call overhead. The optimization splits the existing cuPythonInit() and cudaPythonInit() functions into two parts: a small wrapper function that checks if initialization has already occurred, and a larger function that performs the actual initialization work.

• Refactors initialization functions to use a small wrapper pattern for better compiler inlining
• Moves the initialization flag check to a separate small function to enable C compiler optimization
• Applies the same pattern across three binding files for consistency

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
cyruntime.pyx.in	Splits cudaPythonInit() into wrapper and implementation functions
cynvrtc.pyx.in	Splits cuPythonInit() into wrapper and implementation functions
cydriver.pyx.in	Splits cuPythonInit() into wrapper and implementation functions

Comments suppressed due to low confidence (1)

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[mdboom]

/ok to test

[github-actions]

Doc Preview CI
🚀 View preview at https://nvidia.github.io/cuda-python/pr-preview/pr-894/
https://nvidia.github.io/cuda-python/pr-preview/pr-894/cuda-core/
https://nvidia.github.io/cuda-python/pr-preview/pr-894/cuda-bindings/
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[leofang]

Let's also add a release note to 13.X.Y. (I want to backport it to 12.9.X, so perhaps also a good idea to touch its release note. Note that we only generate docs on the main branch #809.)

Also we need to backport this to the codegen 🙂

[mdboom]

Let's also add a release note to 13.X.Y. (I want to backport it to 12.9.X, so perhaps also a good idea to touch its release note. Note that we only generate docs on the main branch #809.)

👍

Also we need to backport this to the codegen 🙂

Sure, will do. The upstream of the generator at [email protected]:NVIDIA/cuda-python-private.git doesn't seem to have the free-threading fix yet (so running the generator for this change reverts all that). Is that just because that fix hasn't been implemented in the generator yet, or am I using the wrong branch or something on my end?

[leofang]

I guess you're blocked by me now... let me get to it asap

[leofang]

/ok to test 4c6a057