[Platform][Refactor] Extract func get_default_attn_backend to Platform

[MengqingCao]

Extrct func get_default_attn_backend to Platform and implement it on different backends.

Part of #9268

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[youkaichao]

LGTM, thanks for the refactor!

[DarkLight1337]

PTAL at the failing kernels tests. You can ignore the HF connection errors.

[mergify]

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

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

[MengqingCao]

PTAL at the failing kernels tests. You can ignore the HF connection errors.

Well, when getting the default attention backend via the current_platform runtime instance, we can no longer mock different backends via mock vllm.attention.selector.current_platform.is_cpu. I will take a look at how to change the test cases to adapt to the current changes.

[youkaichao]

maybe you can directly mock which_attn_to_use

[MengqingCao]

maybe you can directly mock which_attn_to_use

Won't this invalidate the test? I mean this might skip the actual execution of the test.

[youkaichao]

Won't this invalidate the test?

good point.

maybe:

if device == "cpu":
    from vllm.platforns.cpu import CpuPlatform
    with patch("vllm.platforms.current_platform", CpuPlatform()):

[MengqingCao]

if device == "cpu":
    from vllm.platforns.cpu import CpuPlatform
    with patch("vllm.platforms.current_platform", CpuPlatform()):

Thanks! Mocking current_platform works, but with a slight change, i.e. we need to mock vllm.attention.selector.current_platform

[mergify]

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

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

[MengqingCao]

CI failed because VllmConfig was not set before calling CustomOp. I'll fix this in the next commit.

[MengqingCao]

I fixed the UTs in tests/kernels/test_layernorm.py, tests/kernels/test_activation.py, tests/kernels/test_pos_encoding.py and tests/kernels/test_rotary_embedding.py

However, I have some trouble in triton now. Thus, I didn't fix tests/kernels/test_moe.py and tests/kernels/test_awq_marlin.py

@youkaichao Could you help fix the remaining UTs in tests/kernels/test_moe.py and tests/kernels/test_awq_marlin.py ?

[youkaichao]

@MengqingCao sorry for the trouble. these errors should be fixed by #10431 . please merge main to fix the test error. and you can revert the changes to tests/kernels/test_rotary_embedding.py etc.

[MengqingCao]

@MengqingCao sorry for the trouble. these errors should be fixed by #10431 . please merge main to fix the test error. and you can revert the changes to tests/kernels/test_rotary_embedding.py etc.

Thanks, got it