Three initialization and config defects found serving Qwen4Exp, each with a
regression test.
**The MTP hidden buffer lands on the ambient device.** torch.empty for the
spec-decode hidden buffer takes no device, so it follows whatever device is
current rather than vllm_config.device_config.device. The allocation was
duplicated verbatim in the NVIDIA and AMD backends; it moves to
common/mtp.py so the two cannot drift, and the caller passes is_last_rank
rather than reaching for the process group from shared code.
**M-RoPE keys are reported as unrecognized.** Qwen4Exp drives M-RoPE through
mrope_section and mrope_interleaved, which transformers' rope validator does
not know for rope_type="default", so every load warns about a configuration
the model genuinely uses. Declare them at rope validation on the text config
and on the outer config that mirrors it; every other key still warns.
**transformers' layer_types spelling is unread.** Its Qwen4Exp config
canonicalizes "full_attention" entries to "qwen_sparse_attention" in memory,
so checkpoints re-exported through it serialize that name. vLLM keys QSA off
"full_attention" plus indexer_n_heads, so map the spelling back.
**Qwen4Exp is missing from the Triton warmup set.** Its GDN prefill and QSA
run on other backends, but the kernels this warmup covers -- the gated RMS
norm, the causal conv, the post-conv preparation, the decode state update --
are Triton whichever prefill kernel is chosen, so they compile on the first
prompt instead. qwen4_exp_mtp stays out: kernel_warmup passes the worker's
own model_config, which is the target model's.
tests/models/qwen4_exp/test_config.py: 15 passed.
tests/model_executor/test_qwen_triton_warmup.py: 6 passed.
ruff check, ruff format --check and mypy (Python 3.10) report what they
already report on the base commit.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: lesj0610 <lesj0610@users.noreply.github.com>
