[Minor][Spec Decode] Add use_eagle to SpeculativeConfig (#17213)

Signed-off-by: Woosuk Kwon <woosuk.kwon@berkeley.edu>

vllm/config.py

@@ -2566,6 +2566,9 @@ class SpeculativeConfig:
         """
         return self.num_speculative_tokens
 
+    def use_eagle(self) -> bool:
+        return self.method in ("eagle", "eagle3")
+
     def __repr__(self) -> str:
         method = self.method
         model = None if method == "ngram" else self.draft_model_config.model

vllm/v1/core/sched/scheduler.py

@@ -126,7 +126,7 @@ class Scheduler(SchedulerInterface):
         self.num_spec_tokens = self.num_lookahead_tokens = 0
         if speculative_config:
             self.num_spec_tokens = speculative_config.num_speculative_tokens
-            if speculative_config.method in ("eagle", "eagle3"):
+            if speculative_config.use_eagle():
                 self.num_lookahead_tokens = self.num_spec_tokens
 
     def schedule(self) -> SchedulerOutput:

vllm/v1/worker/gpu_model_runner.py

@@ -171,8 +171,7 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             if get_pp_group().is_last_rank:
                 if self.speculative_config.method == "ngram":
                     self.drafter = NgramProposer(self.vllm_config)
-                elif self.speculative_config.method == "eagle" or \
-                        self.speculative_config.method == "eagle3":
+                elif self.speculative_config.use_eagle():
                     self.drafter = EagleProposer(self.vllm_config,
                                                  self.device)  # type: ignore
                     if self.speculative_config.method == "eagle3":
@@ -1192,8 +1191,7 @@ class GPUModelRunner(LoRAModelRunnerMixin):
             assert isinstance(self.drafter, NgramProposer)
             spec_token_ids = self.generate_draft_token_ids(
                 valid_sampled_token_ids, sampling_metadata)
-        elif self.speculative_config.method == "eagle" or \
-                self.speculative_config.method == "eagle3":
+        elif self.speculative_config.use_eagle():
             assert isinstance(self.drafter, EagleProposer)
             # TODO(woosuk): Refactor the loop.
             next_token_ids: list[int] = []