[GLM5.3 Perf] Inplace update draft decode metadata, 1.7% E2E Throughput Improvement (#61873)

Signed-off-by: yewentao256 <zhyanwentao@126.com>

vllm/v1/attention/backends/mla/flashinfer_mla_sparse.py

@@ -35,6 +35,7 @@ from vllm.v1.attention.backends.mla.sparse_utils import (
     flat_kv_row_view,
     prepare_sparse_mla_safe_lengths,
 )
+from vllm.v1.attention.ops.metadata import compute_token_to_req_indices
 from vllm.v1.kv_cache_interface import AttentionSpec, KVCacheSpec
 
 if TYPE_CHECKING:
@@ -297,6 +298,11 @@ class FlashInferMLASparseTRTLLMMetadataBuilder(FlashInferMLASparseMetadataBuilde
         device: torch.device,
     ) -> None:
         super().__init__(kv_cache_spec, layer_names, vllm_config, device)
+        self.supports_draft_decode_metadata_update = (
+            self.dcp_world_size == 1
+            and self.pcp_world_size == 1
+            and vllm_config.attention_config.hisparse_config is None
+        )
 
         # Under DCP the workspace must hold the trtllm-gen softmax-stats slab.
         # The buffer address is baked into CUDA graphs, so it has to reach its
@@ -314,6 +320,18 @@ class FlashInferMLASparseTRTLLMMetadataBuilder(FlashInferMLASparseMetadataBuilde
                 ),
             )
 
+    def update_draft_decode_metadata(
+        self, metadata: FlashInferMLASparseMetadata
+    ) -> None:
+        num_tokens = metadata.num_decode_tokens
+        if num_tokens:
+            compute_token_to_req_indices(
+                metadata.query_start_loc,
+                metadata.req_id_per_token,
+                num_tokens,
+                num_tokens,
+            )
+
 
 # Global workspace buffer (lazily initialized)
 _fi_sparse_workspace: torch.Tensor | None = None