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vllm-project#49649) AITER has no non-persistent sparse-MLA decode kernel for gqa_ratio=64 fp8/fp8 (asm_mla.cu:949: "fp8/fp8 with gqa_ratio=64 only supports persistent mode"). A persistent-kernel gate that falls back to the non-persistent split-KV path for such groupings (e.g. chunked-prefill continuations, cf. vllm-project#47567) crashes the prefill worker deterministically for GLM-5.1-FP8 DSA disaggregated serving (DP=8/TP=1 => gqa_ratio=64). Adds `sparse_mla_requires_persistent(num_heads_per_head_k, kv_cache_dtype)` that encodes the invariant, and a fail-fast guard in the sparse-MLA decode path that raises a clear error (pointing to vllm-project#49649) if persistent metadata is ever absent for a persistent-only grouping, instead of the opaque asm_mla.cu:949 kernel crash. main is already always-persistent, so this is a safety net that keeps a future gate from silently breaking gqa_ratio=64 fp8. Includes a CPU-only reproducer/regression test for the decision function. Refs vllm-project#49649 (also vllm-project#47567, vllm-project#47766, ROCm/aiter#4076). Signed-off-by: Mohit Deopujari <Mohit.Deopujari@amd.com>
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Purpose
Fixes #49649.
AITER has no non-persistent sparse-MLA decode kernel for
gqa_ratio == 64fp8/fp8:A persistent-kernel gate that falls back to the non-persistent split-KV MLA path for such groupings (e.g. the chunked-prefill-continuation fallback discussed in #47567) therefore crashes the prefill worker deterministically for GLM-5.1-FP8 DSA disaggregated serving at
data_parallel_size=8, tensor_parallel_size=1(per-rankgqa_ratio=64), surfacing downstream as a gloo "Connection reset by peer" in DP coordination.main'srocm_aiter_mla_sparse.py::build()is already always-persistent (it always precomputeswork_meta_data), so this PR is a safety net that encodes the invariant rather than a behavior change onmain: it makes any future gate that would drop persistent metadata for a persistent-only grouping fail fast with a clear message instead of the opaqueasm_mla.cu:949kernel crash.Changes
sparse_mla_requires_persistent(num_heads_per_head_k, kv_cache_dtype)invllm/v1/attention/backends/mla/rocm_aiter_mla_sparse.py— returnsTrueforgqa_ratio==64+ fp8 (persistent-only).ROCMAiterMLASparseImpl._forward_mla: ifwork_meta_dataisNonefor a persistent-only grouping, raise a clearValueErrorpointing to this issue (instead of letting the kernel OOB/abort).tests/kernels/attention/test_rocm_aiter_mla_sparse_persistent_guard.pycovering the decision function (no ROCm/AITER/GPU required).Recommendation for gate authors
If #47567 (or any persistent-kernel gate) lands, skip the gate when the head grouping has no non-persistent kernel — i.e. keep
use_persistent = Trueforgqa_ratio == 64fp8. This preservesmain's current (correct) behavior for that config. Note #47766 (6-field sparse-MLA metadata key) already makes the persistent kernel correct across chunked prefill — validated with NIAH up to 96k on both 1P1D EP8 and 2P2D EP16.Test
pytest tests/kernels/attention/test_rocm_aiter_mla_sparse_persistent_guard.py(CPU-only).Env where the crash was observed: ROCm 7.2.3, MI300X (gfx942), vLLM 0.25.1 + #47766, AITER v0.1.18, MoRI 1.1.2.dev43+g42e895472, GLM-5.1-FP8.
Related: #49649, #47567, #47766, ROCm/aiter#4076.