Intake of open upstream PR vllm-project/vllm#58449.
With MTP num_speculative_tokens > 1, the V2 autoregressive speculator
reuses one attention-metadata build across draft steps only when every
group's builder sets supports_draft_decode_metadata_update. The QSA
side-cache builder (QWEN4_EXP_EXP_QSA_STATE) did not, so every draft
step rebuilt attention metadata for the whole model.
QSAMetadataBuilder now implements update_draft_decode_metadata: it
re-launches the kernel with in-place seq_lens updates, so one metadata
build serves every draft step.
Co-Authored-By: Hinata <hinata@idihore.id>
Signed-off-by: MOVZX <movzx@yahoo.com>
QSAMetadataBuilder did not set supports_draft_decode_metadata_update, so
MTP with num_speculative_tokens > 1 fell back to rebuilding attention
metadata between draft steps for the whole model.
Opt the builder in. update_draft_decode_metadata re-launches the builder's
own _build_qsa_metadata_kernel in place on the metadata's persistent
tensors, so draft-step token_to_req, logical_positions, visible_blocks,
slot_mapping and k_work_metadata come from the same code path as build().
The kernel launch is factored into _launch_qsa_metadata_kernel, and
QSAForwardMetadata carries common_slot_mapping and num_mapped_tokens so
the update does not read query_start_loc_cpu. The PyTorch fallback builder
keeps the rebuild path.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Signed-off-by: bilikas <valdas@vbtech.eu>
MOVZX
