[Spec] Support FlashInfer CUDA graph for EAGLE draft-extend (#28782)

python/sglang/srt/layers/attention/flashinfer_backend.py

@@ -572,6 +572,18 @@ class FlashInferAttnBackend(AttentionBackend):
                 encoder_lens=encoder_lens[:bs] if encoder_lens is not None else None,
                 spec_info=None,
             )
+        elif forward_mode.is_draft_extend_v2():
+            self.indices_updater_prefill.update(
+                req_pool_indices[:bs],
+                seq_lens[:bs],
+                seq_lens_cpu[:bs] if seq_lens_cpu is not None else None,
+                seq_lens_sum,
+                prefix_lens=None,
+                prefill_wrappers=self.draft_extend_cuda_graph_metadata[bs],
+                use_ragged=False,
+                encoder_lens=encoder_lens[:bs] if encoder_lens is not None else None,
+                spec_info=spec_info,
+            )
         else:
             raise ValueError("Invalid forward mode")
 
@@ -678,6 +690,7 @@ class FlashInferAttnBackend(AttentionBackend):
                 fixed_split_size=self.prefill_split_tile_size,
                 multi_item_params=multi_item_params,
                 cross_attention_custom_mask=forward_batch.cross_attention_custom_mask,
+                extend_prefix_lens_cpu=forward_batch.extend_prefix_lens_cpu,
             )
             self.forward_metadata = PrefillMetadata(
                 self.prefill_wrappers_paged,
@@ -797,6 +810,11 @@ class FlashInferAttnBackend(AttentionBackend):
             self.forward_metadata = PrefillMetadata(
                 prefill_wrappers, forward_mode.is_dllm_extend(), False
             )
+        elif forward_mode.is_draft_extend_v2():
+            # Draft-extend: causal paged prefill over the full sequence (no mask).
+            prefill_wrappers = self._create_prefill_wrappers(bs, use_custom_mask=False)
+            self.draft_extend_cuda_graph_metadata[bs] = prefill_wrappers
+            self.forward_metadata = PrefillMetadata(prefill_wrappers, False, False)
         else:
             raise ValueError(f"Invalid mode: {forward_mode=}")
 
@@ -1306,6 +1324,7 @@ class FlashInferIndicesUpdaterPrefill:
         fixed_split_size: Optional[int] = None,
         multi_item_params: Optional[MultiItemScoringParams] = None,
         cross_attention_custom_mask: Optional[torch.Tensor] = None,
+        extend_prefix_lens_cpu: Optional[List[int]] = None,
     ):
         # Keep the signature for type checking. It will be assigned during runtime.
         raise NotImplementedError()
@@ -1324,13 +1343,16 @@ class FlashInferIndicesUpdaterPrefill:
         fixed_split_size: Optional[int] = None,
         multi_item_params: Optional[MultiItemScoringParams] = None,
         cross_attention_custom_mask: Optional[torch.Tensor] = None,
+        extend_prefix_lens_cpu: Optional[List[int]] = None,
     ):
         if use_ragged:
             assert prefix_lens is not None
-            # TODO: remove this device sync, we can use forward_batch.extend_prefix_lens_cpu
-            # and forward_batch.extend_seq_lens_cpu
             paged_kernel_lens = prefix_lens
-            paged_kernel_lens_sum = paged_kernel_lens.sum().item()
+            if extend_prefix_lens_cpu is not None:
+                # Host-known prefix lens; avoids a per-step D2H sync.
+                paged_kernel_lens_sum = sum(extend_prefix_lens_cpu)
+            else:
+                paged_kernel_lens_sum = paged_kernel_lens.sum().item()
         else:
             paged_kernel_lens = seq_lens
             paged_kernel_lens_sum = seq_lens_sum
@@ -1366,6 +1388,7 @@ class FlashInferIndicesUpdaterPrefill:
         fixed_split_size: Optional[int] = None,
         multi_item_params: Optional[MultiItemScoringParams] = None,
         cross_attention_custom_mask: Optional[torch.Tensor] = None,
+        extend_prefix_lens_cpu: Optional[List[int]] = None,
     ):
         if prefix_lens is None:
             num_accept_tokens = getattr(spec_info, "num_accept_tokens", None)
@@ -1486,6 +1509,7 @@ class FlashInferIndicesUpdaterPrefill:
         fixed_split_size: Optional[int] = None,
         multi_item_params: Optional[MultiItemScoringParams] = None,
         cross_attention_custom_mask: Optional[torch.Tensor] = None,
+        extend_prefix_lens_cpu: Optional[List[int]] = None,
     ):
         for wrapper_id in range(2):
             if wrapper_id == 0:

python/sglang/srt/speculative/eagle_draft_extend_cuda_graph_runner.py

@@ -340,6 +340,8 @@ class EAGLEDraftExtendCudaGraphRunner(DecodeCudaGraphRunner):
             hidden_states=hidden_states,
             num_correct_drafts=num_correct_drafts,
             num_accept_tokens=num_accept_tokens,
+            # Padded tree width per req; drives the constant qo layout.
+            num_tokens_per_req=self.num_tokens_per_bs,
         )
 
         forward_batch = ForwardBatch(

python/sglang/srt/speculative/eagle_info.py

@@ -418,8 +418,14 @@ class EagleDraftExtendInput(SpecInput):
     ):
         device = req_pool_indices.device
         bs = self.num_correct_drafts.numel()
-        qo_indptr = torch.zeros((bs + 1,), dtype=torch.int32, device=device)
+        # Constant num_tokens_per_req qo layout (required for cuda-graph capture).
-        qo_indptr[1:] = torch.cumsum(self.num_accept_tokens, dim=0)
+        qo_indptr = torch.arange(
+            0,
+            (bs + 1) * self.num_tokens_per_req,
+            step=self.num_tokens_per_req,
+            dtype=torch.int32,
+            device=device,
+        )
         cum_kv_seq_len = torch.zeros((bs + 1,), dtype=torch.int32, device=device)
         cum_kv_seq_len[1:] = torch.cumsum(paged_kernel_lens, dim=0)
 

python/sglang/srt/speculative/eagle_worker_v2.py

@@ -14,6 +14,7 @@ from sglang.srt.hardware_backend.npu.graph_runner.eagle_draft_npu_graph_runner i
 )
 from sglang.srt.hardware_backend.npu.graph_runner.npu_graph_runner import NPUGraphRunner
 from sglang.srt.kv_canary.runner.canary_manager import context_tuple
+from sglang.srt.layers.attention.flashinfer_backend import FlashInferAttnBackend
 from sglang.srt.layers.attention.tokenspeed_mla_backend import TokenspeedMLABackend
 from sglang.srt.layers.attention.triton_backend import TritonAttnBackend
 from sglang.srt.layers.attention.trtllm_mha_backend import TRTLLMHAAttnBackend
@@ -407,8 +408,9 @@ class EagleDraftWorker(EagleDraftWorkerBase):
                 self.draft_attn_backend, AiterMultiStepDraftBackend
             )
 
-        supports_cuda_draft_extend_graph = (_is_cuda or _is_musa) and isinstance(
+        draft_extend_backend = self.draft_extend_attn_backend
-            self.draft_extend_attn_backend,
+        graph_supported_backend = isinstance(
+            draft_extend_backend,
             (
                 TritonAttnBackend,
                 TRTLLMMLABackend,
@@ -416,6 +418,15 @@ class EagleDraftWorker(EagleDraftWorkerBase):
                 TokenspeedMLABackend,
             ),
         )
+        # FlashInfer draft-extend graph does not support a reduced draft vocab
+        # (speculative_token_map / FR-Spec); fall back to eager in that case.
+        flashinfer_graph_supported = (
+            isinstance(draft_extend_backend, FlashInferAttnBackend)
+            and self.server_args.speculative_token_map is None
+        )
+        supports_cuda_draft_extend_graph = (_is_cuda or _is_musa) and (
+            graph_supported_backend or flashinfer_graph_supported
+        )
         # Capture extend
         # TODO: support draft extend cuda graph for more attention backends
         if self.draft_extend_attn_backend and (