[Platform] allow platform to init dp group

[wangxiyuan]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

When init dp group, it's always set to "gloo", we should allow platform to init dp group by itself. This PR allow platform init dp group and fallback to "gloo" if failed.

For cuda platfrom, stateless_init_device_torch_dist_pg is not used anywhere, let's remove it now.

Test Plan

Test Result

(Optional) Documentation Update

[gemini-code-assist]

Code Review

This pull request refactors the data parallel process group initialization to be platform-specific, allowing different backends like nccl on GPUs. The change is generally good, but I've identified a critical issue in the error handling. The current implementation could silently fall back to the gloo backend if a platform-specific initialization (e.g., nccl) fails, potentially masking errors and causing severe performance degradation. I've suggested a more robust error handling mechanism to prevent this.

[github-actions]

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[DarkLight1337]

PTAL at the test failure

[wangxiyuan]

@DarkLight1337 Thanks for the quick reply. the problem seems caused by gloo to nccl chaning. I'll take a look ASAP

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @wangxiyuan.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[hmellor]

FYI the ParallelConfig has moved to vllm/config/parallel.py

[wangxiyuan]

@hmellor thanks for the reminding. And we've figured out the CI problem @zhaowei1936 will rebase and keep working on this PR.

[DarkLight1337]

Please merge from main to fix merge conflict

[hmellor]

Failing test is the flaky tool choice one