[ROCm][Spec Decode] Fix probabilistic draft probs test attention backend

[stefankoncarevic]

Purpose

test_propose_stores_probabilistic_draft_probs hardcodes the FLASH_ATTN
attention backend, which builds FlashAttentionMetadata. On ROCm, the
speculative-decoding proposer only accepts Triton/Rocm/AITER metadata
(allowed_attn_types is built under current_platform.is_rocm() in
vllm/v1/spec_decode/llm_base_proposer.py), so the test fails on AMD MI
architectures (gfx942 / MI325, gfx950 / MI355) with:

ValueError: Unsupported attention metadata type for speculative decoding
with num_speculative_tokens > 1: FlashAttentionMetadata. Supported types
are: (TritonAttentionMetadata, RocmAttentionMetadata, ...,
AiterFlashAttentionMetadata, ...)

The fix selects TRITON_ATTN on ROCm and keeps FLASH_ATTN on CUDA,
matching the per-backend pattern already used by test_propose in the
same file. No behavior change on CUDA.

Test Plan

pytest -x -v tests/v1/spec_decode/test_eagle.py::test_propose_stores_probabilistic_draft_probs

Run on ROCm (gfx950 / MI355).

Test Result

Before (ROCm, gfx950 / MI355):

FAILED tests/v1/spec_decode/test_eagle.py::test_propose_stores_probabilistic_draft_probs
ValueError: Unsupported attention metadata type for speculative decoding ... FlashAttentionMetadata
vllm/v1/spec_decode/llm_base_proposer.py:568: ValueError

After (ROCm, gfx950 / MI355):

tests/v1/spec_decode/test_eagle.py::test_propose_stores_probabilistic_draft_probs PASSED
1 passed in 8.81s

This is the only failing test in the tests/v1/spec_decode/ group on ROCm
(141 passed, 1 failed before the fix), so the change turns the V1 Spec
Decode group green on AMD. The same failure was also confirmed on
gfx942 / MI325. CUDA is unaffected (still uses FLASH_ATTN).

---

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[AndreasKaratzas]

Also, under

https://github.com/vllm-project/vllm/blob/main/.buildkite/test_areas/spec_decode.yaml#L1-L14

can you add

...
  mirror:
    amd:
      device: mi300_1
      timeout_in_minutes: 65
      depends_on:
      - image-build-amd
      source_file_dependencies:
      - vllm/v1/spec_decode/
      - vllm/v1/worker/gpu/spec_decode/
      - vllm/model_executor/model_loader/
      - vllm/v1/sample/
      - vllm/model_executor/layers/
      - tests/v1/e2e/spec_decode/
      - vllm/platforms/rocm.py

[AndreasKaratzas]

Can we maybe make the backends to test a list under a @pytest.mark.parametrize setting? For ROCm use both ROCM_ATTN and TRITON_ATTN, and for CUDA FLASH ATTN. Mostly to include the default backend too in the test cadence.

[stefankoncarevic]

Done, switched to @pytest.mark.parametrize. On ROCm it now runs both ROCM_ATTN and TRITON_ATTN, and on CUDA FLASH_ATTN, so the default backend is covered too. Verified locally on MI355 (gfx950): both ROCm cases pass (2 passed).

[stefankoncarevic]

Also, under

https://github.com/vllm-project/vllm/blob/main/.buildkite/test_areas/spec_decode.yaml#L1-L14

can you add

...
  mirror:
    amd:
      device: mi300_1
      timeout_in_minutes: 65
      depends_on:
      - image-build-amd
      source_file_dependencies:
      - vllm/v1/spec_decode/
      - vllm/v1/worker/gpu/spec_decode/
      - vllm/model_executor/model_loader/
      - vllm/v1/sample/
      - vllm/model_executor/layers/
      - tests/v1/e2e/spec_decode/
      - vllm/platforms/rocm.py

Added the AMD mirror for the Spec Decode Eagle step on mi300_1 in spec_decode.yaml, matching the other mirrored steps.
Could you add the ready label when you get a chance so CI can run? Thanks!

[AndreasKaratzas]

Thank you @mawong-amd for the correction.
@stefankoncarevic I gave you the wrong file to gate, apologies. The test to target is under:

vllm/.buildkite/test_areas/misc.yaml

Line 23 in 9c7c74b

- pytest -v -s -m 'not slow_test' v1/spec_decode

And it resolves:
https://buildkite.com/vllm/amd-ci/builds/9636/list?sid=019ed4cf-5bb1-47f7-83ea-f4a258bf43a7&tab=output

[stefankoncarevic]

Thank you @mawong-amd for the correction. @stefankoncarevic I gave you the wrong file to gate, apologies. The test to target is under:

vllm/.buildkite/test_areas/misc.yaml

Line 23 in 9c7c74b

- pytest -v -s -m 'not slow_test' v1/spec_decode

And it resolves: https://buildkite.com/vllm/amd-ci/builds/9636/list?sid=019ed4cf-5bb1-47f7-83ea-f4a258bf43a7&tab=output

Thanks @mawong-amd and @AndreasKaratzas for the catch, you're right, the "Spec Decode Eagle" group only runs the e2e tests and doesn't cover tests/v1/spec_decode/test_eagle.py. I moved the AMD mirror to the V1 Spec Decode step in misc.yaml, so the fix is now actually gated on AMD.

[AndreasKaratzas]

LGTM