[V1][PP] Fix & Pin Ray version in requirements-cuda.txt

[WoosukKwon]

Pipeline parallelism in V1 requires ray[adag] instead of ray[default].
Also, because of the API changes in 2.42.0, we have to pin the version to 2.41.0 (or 2.40.0).

NOTE: Importantly, having ray[adag] will add CuPy (cu12) as a dependency. Since PP is not used for all models, we can consider keeping ray[adag] as an optional dependency if it's not acceptable.

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[comaniac]

cc @ruisearch42 @richardliaw

[youkaichao]

i think it’s fine, as long as vllm does not directly use cupy .
one thing about cupy is, it has cupy-cuda11x and cupy-cuda12x . I’m not sure how ray deals with it. will it break the cuda 11.8 build of vllm?

[WoosukKwon]

@youkaichao It seems to use cupy-cu12. However, IIUC, it doesn't break anything on our cu11.8 build unless the user explicitly chooses Ray?

[youkaichao]

@youkaichao It seems to use cupy-cu12. However, IIUC, it doesn't break anything on our cu11.8 build unless the user explicitly chooses Ray?

sounds good, then it's a ray-related issue, whether they want to support cuda 11.8 . we can go ahead with ray[adag] .

[ruisearch42]

ray[adag] uses cupy-cuda12x. BTW, there is an issue in ray 2.42 and is being fixed. After that we can upgrade to the latest version with a small API change.

[darthhexx]

The issue with pinning to a specific Ray version is that anyone with a long running cluster will not be able to upgrade vLLM services unless they upgrade the entire Ray cluster.

Please can we rather look at a range specifier (i.e. ray[adag]>=2.43.0), once 2.43.0 comes out with the fix?

[ruisearch42]

Hi @darthhexx , that makes sense. This is a short term fix and the plan is to support a ray version range.