[ROCm][MoE] Route batched expert layout through flat-reshape wrapper for AITER FP8

[chaeminlim-mb]

Purpose

Enable ROCm AITER FP8 MoE when the prepare/finalize path produces BatchedExperts activations, such as deepep_low_latency and nixl_ep. The existing AiterExperts kernel only advertises Standard activations, so AITER could not be selected for those batched expert layouts.

Test Plan

Primary vLLM serve shape for this path:

VLLM_ROCM_USE_AITER=1 VLLM_ROCM_USE_AITER_MOE=1 \
vllm serve <local DeepSeek-R1-FP8 checkpoint> \
  --trust-remote-code \
  --tensor-parallel-size 1 \
  --data-parallel-size 16 \
  --data-parallel-size-local 8 \
  --enable-expert-parallel \
  --all2all-backend deepep_low_latency \
  --moe-backend aiter \
  --max-model-len 1024 \
  --max-num-batched-tokens 1024

Targeted checks:

python3 -m py_compile \
  vllm/model_executor/layers/fused_moe/config.py \
  vllm/model_executor/layers/fused_moe/experts/rocm_aiter_moe.py \
  vllm/model_executor/layers/fused_moe/oracle/fp8.py \
  vllm/model_executor/layers/quantization/fp8.py \
  tests/kernels/moe/test_aiter_batched_experts.py

python3 -m pytest -q tests/kernels/moe/test_aiter_batched_experts.py

Test Result

• ROCm/AITER containers on two 8-GPU nodes: 18 passed on each node.
• Installed-package ROCm/AITER smoke on two 8-GPU nodes: auto and explicit moe_backend="aiter" both selected BATCHED_AITER.
• Two-node vllm serve smoke with the command shape above reached Using BATCHED_AITER Fp8 MoE backend and completed checkpoint loading. Request-level readiness was blocked by a DeepEP/rocSHMEM transport bootstrap timeout in the test environment.

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[chaeminlim-mb]

Thanks for the review feedback. I updated the branch to keep the implementation comments focused on the ROCm/AITER path and moved the longer explanation into the PR description.

Changes made:

• Removed the verbose inline comment block from the FP8 oracle priority list.
• Rewrote AiterBatchedExpertsFp8 to have a shorter, self-contained class docstring.
• Moved the longer BatchedExperts/router-weight caveat into a collapsed PR-description note.
• Removed DeepEP/NIXL-specific wording from the ROCm AITER wrapper comments, including the remaining DeepEP-LL example in the latest follow-up commit.

I also kept the short code-site comment explaining that BatchedExperts prepare/finalize owns router weighting and reduction, since that is the non-obvious contract the wrapper depends on.

[chaeminlim-mb]

Follow-up cleanup after the review feedback:

• Fixed the output-dimension typo in the batched-experts assertion text (N -> K) and added an explicit check plus a contiguity assertion.
• Switched from to so the inner AITER kernel is guaranteed to write into the runtime-allocated output buffer rather than a temporary copy.
• Removed the unnecessary markers in the unit test and consolidated imports.

No behavioral change in the tested TP8/DP8EP paths; this is defensive hardening for the output-buffer aliasing contract.

[chaeminlim-mb]

Clarifying the previous follow-up comment with the code fragments that the shell ate:

• Added assert output.shape == hidden_states.shape and assert output.is_contiguous() before flattening.
• Changed flat_out = output.reshape(E_local * M_e, output.size(-1)) to flat_out = output.view(E_local * M_e, K) so the inner AITER kernel writes directly into the runtime-allocated output buffer.
• Removed the unnecessary # noqa: E402 markers in tests/kernels/moe/test_aiter_batched_experts.py and consolidated the import block.

[chaeminlim-mb]

Co-authored by @edwinlim0919 (Edwin Lim, MangoBoost) — credited in the commit trailers for this PR. Tagging him here so he is looped in and can follow the review.

[AndreasKaratzas]

There is no skip for non rocm platforms here, or did I miss something?

[chaeminlim-mb]

Thanks for catching this. I should have made the intent clearer. This file is intended as CPU-level wrapper/oracle coverage, not a ROCm kernel test. The inner AITER call is stubbed out, and the oracle path is monkeypatched, so it should be safe and useful on non-ROCm CI as import/routing coverage. If you’d prefer this to match the ROCm-specific test convention, I’m happy to add a module-level skip before the AITER imports.

[AndreasKaratzas]

Please take some time to read my comment instead of generating one. An aiter test regardless of what the test should be skipped on non rocm platforms as well as on platforms that do not support AITER (eg mi250)

[chaeminlim-mb]

You are right, I missed the actual point. I added a module-level guard before the ROCm AITER imports so the test is skipped on non-ROCm and on ROCm platforms without supported AITER. I also trimmed the wrapper comments so the code keeps only the local contract.

[tjtanaa]

Keep these comments.

[tjtanaa]

we shouldn't just use the function as it is semantically incorrect. The flag is for flash infer (CUDA)

vllm/vllm/model_executor/layers/fused_moe/config.py

Lines 1052 to 1056 in 04c2a8d

	@property
	def use_fi_nvl_two_sided_kernels(self):
	return self.use_all2all_kernels and (
	self.all2all_backend == "flashinfer_all2allv"
	or self.all2all_backend == "flashinfer_nvlink_two_sided"

vllm/vllm/model_executor/layers/fused_moe/config.py

Lines 1060 to 1064 in 04c2a8d

	def use_fi_nvl_one_sided_kernels(self):
	return (
	self.use_all2all_kernels
	and self.all2all_backend == "flashinfer_nvlink_one_sided"
	)

Please define new enum and property based on current situation.

[tjtanaa]

Please provide more input test case (with sufficient test configurations) to validate the logics, not just a single config.

Example:
https://github.com/vllm-project/vllm/blob/main/tests/kernels/moe/test_deepep_moe.py#L437-L458

[mergify]

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

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

[AndreasKaratzas]

I just came from another PR of yours. It looks to me that your PRs have minimal human involvement. Please revamp all your PRs wrt the architecture and procedure of this open source community.

[chaeminlim-mb]

After re-evaluating this PR against the deployment path I need to validate, I no longer think this change is the right one to pursue.

I verified backend selection on both upstream and this branch for the MoRI EP path. It continues to use the existing AITER backend selection there, so this PR does not provide the right coverage or value for that work.

Keeping this PR open would add code and tests for a path I am not pursuing. I am closing it and will focus validation/fixes on the actual MoRI EP path separately.