[feat] Add P/D attention select for draft model (#9755)

Co-authored-by: 纬杭 <ximing.wxm@antgroup.com>

python/sglang/srt/speculative/eagle_worker.py

@@ -187,137 +187,183 @@ class EAGLEWorker(TpModelWorker):
         self.has_prefill_wrapper_verify = False
         self.draft_extend_attn_backend = None
 
-        if self.server_args.attention_backend == "flashinfer":
+        # Initialize decode attention backend
+        self.draft_attn_backend = self._create_decode_backend()
+
+        # Initialize prefill attention backend
+        self.draft_extend_attn_backend = self._create_draft_extend_backend()
+
+        self.draft_model_runner.draft_attn_backend = self.draft_attn_backend
+
+    def _create_backend(
+        self, backend_name: str, backend_map: dict, error_template: str
+    ):
+        backend_type = getattr(self.server_args, backend_name)
+        if backend_type is None:
+            backend_type = self.server_args.attention_backend
+
+        if backend_type not in backend_map:
+            raise ValueError(error_template.format(backend_type=backend_type))
+
+        return backend_map[backend_type]()
+
+    def _create_decode_backend(self):
+        backend_map = {
+            "flashinfer": self._create_flashinfer_decode_backend,
+            "triton": self._create_triton_decode_backend,
+            "aiter": self._create_aiter_decode_backend,
+            "fa3": self._create_fa3_decode_backend,
+            "flashmla": self._create_flashmla_decode_backend,
+            "trtllm_mha": self._create_trtllm_mha_decode_backend,
+            "trtllm_mla": self._create_trtllm_mla_decode_backend,
+        }
+
+        return self._create_backend(
+            "decode_attention_backend",
+            backend_map,
+            "EAGLE is not supported in decode attention backend {backend_type}",
+        )
+
+    def _create_draft_extend_backend(self):
+        backend_map = {
+            "flashinfer": self._create_flashinfer_prefill_backend,
+            "triton": self._create_triton_prefill_backend,
+            "aiter": self._create_aiter_prefill_backend,
+            "fa3": self._create_fa3_prefill_backend,
+            "trtllm_mha": self._create_trtllm_mha_prefill_backend,
+            "trtllm_mla": self._create_trtllm_mla_prefill_backend,
+        }
+
+        return self._create_backend(
+            "prefill_attention_backend",
+            backend_map,
+            "EAGLE is not supported in prefill attention backend {backend_type}",
+        )
+
+    def _create_flashinfer_decode_backend(self):
         if not global_server_args_dict["use_mla_backend"]:
             from sglang.srt.layers.attention.flashinfer_backend import (
-                    FlashInferAttnBackend,
                 FlashInferMultiStepDraftBackend,
             )
 
-                self.draft_attn_backend = FlashInferMultiStepDraftBackend(
-                    self.draft_model_runner,
-                    self.topk,
-                    self.speculative_num_steps,
-                )
-                self.draft_extend_attn_backend = FlashInferAttnBackend(
-                    self.draft_model_runner,
-                    skip_prefill=False,
+            self.has_prefill_wrapper_verify = True
+            return FlashInferMultiStepDraftBackend(
+                self.draft_model_runner, self.topk, self.speculative_num_steps
             )
         else:
             from sglang.srt.layers.attention.flashinfer_mla_backend import (
-                    FlashInferMLAAttnBackend,
                 FlashInferMLAMultiStepDraftBackend,
             )
 
-                self.draft_attn_backend = FlashInferMLAMultiStepDraftBackend(
-                    self.draft_model_runner,
-                    self.topk,
-                    self.speculative_num_steps,
-                )
-                self.draft_extend_attn_backend = FlashInferMLAAttnBackend(
-                    self.draft_model_runner,
-                    skip_prefill=False,
-                )
             self.has_prefill_wrapper_verify = True
-        elif self.server_args.attention_backend == "triton":
+            return FlashInferMLAMultiStepDraftBackend(
+                self.draft_model_runner, self.topk, self.speculative_num_steps
+            )
+
+    def _create_triton_decode_backend(self):
         from sglang.srt.layers.attention.triton_backend import (
-                TritonAttnBackend,
             TritonMultiStepDraftBackend,
         )
 
-            self.draft_attn_backend = TritonMultiStepDraftBackend(
-                self.draft_model_runner,
-                self.topk,
-                self.speculative_num_steps,
-            )
-            self.draft_extend_attn_backend = TritonAttnBackend(
-                self.draft_model_runner,
-                skip_prefill=False,
-            )
-        elif self.server_args.attention_backend == "aiter":
-            from sglang.srt.layers.attention.aiter_backend import (
-                AiterAttnBackend,
-                AiterMultiStepDraftBackend,
+        return TritonMultiStepDraftBackend(
+            self.draft_model_runner, self.topk, self.speculative_num_steps
         )
 
-            self.draft_attn_backend = AiterMultiStepDraftBackend(
-                self.draft_model_runner,
-                self.topk,
-                self.speculative_num_steps,
-            )
-            self.draft_extend_attn_backend = AiterAttnBackend(
-                self.draft_model_runner,
-                skip_prefill=False,
+    def _create_aiter_decode_backend(self):
+        from sglang.srt.layers.attention.aiter_backend import AiterMultiStepDraftBackend
+
+        return AiterMultiStepDraftBackend(
+            self.draft_model_runner, self.topk, self.speculative_num_steps
         )
-            self.has_prefill_wrapper_verify = False
-        elif self.server_args.attention_backend == "fa3":
+
+    def _create_fa3_decode_backend(self):
         from sglang.srt.layers.attention.flashattention_backend import (
-                FlashAttentionBackend,
             FlashAttentionMultiStepBackend,
         )
 
-            self.draft_attn_backend = FlashAttentionMultiStepBackend(
-                self.draft_model_runner,
-                self.topk,
-                self.speculative_num_steps,
-            )
-            self.draft_extend_attn_backend = FlashAttentionBackend(
-                self.draft_model_runner,
-                skip_prefill=False,
+        return FlashAttentionMultiStepBackend(
+            self.draft_model_runner, self.topk, self.speculative_num_steps
         )
-        elif self.server_args.attention_backend == "flashmla":
+
+    def _create_flashmla_decode_backend(self):
         from sglang.srt.layers.attention.flashmla_backend import (
             FlashMLAMultiStepDraftBackend,
         )
 
-            self.draft_attn_backend = FlashMLAMultiStepDraftBackend(
-                self.draft_model_runner,
-                self.topk,
-                self.speculative_num_steps,
+        return FlashMLAMultiStepDraftBackend(
+            self.draft_model_runner, self.topk, self.speculative_num_steps
         )
-        elif self.server_args.attention_backend == "trtllm_mha":
+
+    def _create_trtllm_mha_decode_backend(self):
         from sglang.srt.layers.attention.trtllm_mha_backend import (
-                TRTLLMHAAttnBackend,
             TRTLLMHAAttnMultiStepDraftBackend,
         )
 
-            self.draft_attn_backend = TRTLLMHAAttnMultiStepDraftBackend(
-                self.draft_model_runner,
-                self.topk,
-                self.speculative_num_steps,
-            )
-            self.draft_extend_attn_backend = TRTLLMHAAttnBackend(
-                self.draft_model_runner,
-                skip_prefill=False,
-            )
         self.has_prefill_wrapper_verify = True
-        elif self.server_args.attention_backend == "trtllm_mla":
+        return TRTLLMHAAttnMultiStepDraftBackend(
+            self.draft_model_runner, self.topk, self.speculative_num_steps
+        )
+
+    def _create_trtllm_mla_decode_backend(self):
         if not global_server_args_dict["use_mla_backend"]:
             raise ValueError(
                 "trtllm_mla backend requires MLA model (use_mla_backend=True)."
             )
 
         from sglang.srt.layers.attention.trtllm_mla_backend import (
-                TRTLLMMLABackend,
             TRTLLMMLAMultiStepDraftBackend,
         )
 
-            self.draft_attn_backend = TRTLLMMLAMultiStepDraftBackend(
-                self.draft_model_runner,
-                self.topk,
-                self.speculative_num_steps,
+        self.has_prefill_wrapper_verify = True
+        return TRTLLMMLAMultiStepDraftBackend(
+            self.draft_model_runner, self.topk, self.speculative_num_steps
         )
-            self.draft_extend_attn_backend = TRTLLMMLABackend(
-                self.draft_model_runner,
-                skip_prefill=False,
+
+    def _create_flashinfer_prefill_backend(self):
+        if not global_server_args_dict["use_mla_backend"]:
+            from sglang.srt.layers.attention.flashinfer_backend import (
+                FlashInferAttnBackend,
             )
-            self.has_prefill_wrapper_verify = True
+
+            return FlashInferAttnBackend(self.draft_model_runner, skip_prefill=False)
         else:
+            from sglang.srt.layers.attention.flashinfer_mla_backend import (
+                FlashInferMLAAttnBackend,
+            )
+
+            return FlashInferMLAAttnBackend(self.draft_model_runner, skip_prefill=False)
+
+    def _create_triton_prefill_backend(self):
+        from sglang.srt.layers.attention.triton_backend import TritonAttnBackend
+
+        return TritonAttnBackend(self.draft_model_runner, skip_prefill=False)
+
+    def _create_aiter_prefill_backend(self):
+        from sglang.srt.layers.attention.aiter_backend import AiterAttnBackend
+
+        return AiterAttnBackend(self.draft_model_runner, skip_prefill=False)
+
+    def _create_fa3_prefill_backend(self):
+        from sglang.srt.layers.attention.flashattention_backend import (
+            FlashAttentionBackend,
+        )
+
+        return FlashAttentionBackend(self.draft_model_runner, skip_prefill=False)
+
+    def _create_trtllm_mha_prefill_backend(self):
+        from sglang.srt.layers.attention.trtllm_mha_backend import TRTLLMHAAttnBackend
+
+        return TRTLLMHAAttnBackend(self.draft_model_runner, skip_prefill=False)
+
+    def _create_trtllm_mla_prefill_backend(self):
+        if not global_server_args_dict["use_mla_backend"]:
             raise ValueError(
-                f"EAGLE is not supported in attention backend {self.server_args.attention_backend}"
+                "trtllm_mla backend requires MLA model (use_mla_backend=True)."
             )
 
-        self.draft_model_runner.draft_attn_backend = self.draft_attn_backend
+        from sglang.srt.layers.attention.trtllm_mla_backend import TRTLLMMLABackend
+
+        return TRTLLMMLABackend(self.draft_model_runner, skip_prefill=False)
 
     def init_cuda_graphs(self):
         """Capture cuda graphs."""