[Test] Test multiple attn backend for chunked prefill.

[rkooo567]

Add multi attn backend test for chunked prefill.

I also found the previous approach didin't work because of lru_cache usage

vllm/vllm/attention/selector.py

Line 24 in c2b4a1b

@lru_cache(maxsize=None)

So I instead setting the env var from pipeline.yaml

---

PR Checklist (Click to Expand)

Thank you for your contribution to vLLM! Before submitting the pull request, please ensure the PR meets the following criteria. This helps vLLM maintain the code quality and improve the efficiency of the review process.

PR Title and Classification

Only specific types of PRs will be reviewed. The PR title is prefixed appropriately to indicate the type of change. Please use one of the following:

• [Bugfix] for bug fixes.
• [CI/Build] for build or continuous integration improvements.
• [Doc] for documentation fixes and improvements.
• [Model] for adding a new model or improving an existing model. Model name should appear in the title.
• [Frontend] For changes on the vLLM frontend (e.g., OpenAI API server, LLM class, etc.)
• [Kernel] for changes affecting CUDA kernels or other compute kernels.
• [Core] for changes in the core vLLM logic (e.g., LLMEngine, AsyncLLMEngine, Scheduler, etc.)
• [Hardware][Vendor] for hardware-specific changes. Vendor name should appear in the prefix (e.g., [Hardware][AMD]).
• [Misc] for PRs that do not fit the above categories. Please use this sparingly.

Note: If the PR spans more than one category, please include all relevant prefixes.

Code Quality

The PR need to meet the following code quality standards:

• We adhere to Google Python style guide and Google C++ style guide.
• Pass all linter checks. Please use format.sh to format your code.
• The code need to be well-documented to ensure future contributors can easily understand the code.
• Include sufficient tests to ensure the project to stay correct and robust. This includes both unit tests and integration tests.
• Please add documentation to docs/source/ if the PR modifies the user-facing behaviors of vLLM. It helps vLLM user understand and utilize the new features or changes.

Notes for Large Changes

Please keep the changes as concise as possible. For major architectural changes (>500 LOC excluding kernel/data/config/test), we would expect a GitHub issue (RFC) discussing the technical design and justification. Otherwise, we will tag it with rfc-required and might not go through the PR.

What to Expect for the Reviews

The goal of the vLLM team is to be a transparent reviewing machine. We would like to make the review process transparent and efficient and make sure no contributor feel confused or frustrated. However, the vLLM team is small, so we need to prioritize some PRs over others. Here is what you can expect from the review process:

• After the PR is submitted, the PR will be assigned to a reviewer. Every reviewer will pick up the PRs based on their expertise and availability.
• After the PR is assigned, the reviewer will provide status update every 2-3 days. If the PR is not reviewed within 7 days, please feel free to ping the reviewer or the vLLM team.
• After the review, the reviewer will put an action-required label on the PR if there are changes required. The contributor should address the comments and ping the reviewer to re-review the PR.
• Please respond to all comments within a reasonable time frame. If a comment isn't clear or you disagree with a suggestion, feel free to ask for clarification or discuss the suggestion.

Thank You

Finally, thank you for taking the time to read these guidelines and for your interest in contributing to vLLM. Your contributions make vLLM a great tool for everyone!

[simon-mo]

Can you add other backends as well?

[zhuohan123]

LGTM! Does this change how we run the test locally? If so, can you change the comments on how to run the tests as well?

[rkooo567]

It doesn't change how it is tested locally because in that case, it just uses the default (same as master). But it'd be good to explain how to test different backends, so I will add comments to test files!

[rkooo567]

@simon-mo I found there's torch sdpa and rocm. I assume rocm doesn't make much sense (can it run on cuda gpus?) and sdpa was for cpu? Do you suggest to add sdpa attn backend here?

[simon-mo]

I believe the torch version can serve as a reference implementation. And the rocm is triton based? Please try it and if not working then feel free to remove them.

[rkooo567]

SPDA -> it is not using GPU path anymore; 8afca50. So this PR won't cover it.

ROCM -> there was a bug with naive attention, and I fixed it in this PR.

None native attention + ROCM on GPU seems to fail with odd issue

TypeError: got an unexpected keyword argument 'waves_per_eu'

So I didn't handle it

[rkooo567]

I think the failures are unrelated, and it may be caused by #4012

[jeejeelee]

I think the failures are unrelated, and it may be caused by #4012

I also notice this error, I will process it as soon as possible