[BugFix] Fix min_tokens behaviour for multiple eos tokens (vllm-project#5849)

Author: njhill

vllm/engine/llm_engine.py

@@ -606,12 +606,9 @@ def _create_sequence_group_with_sampling(
         # Defensive copy of SamplingParams, which are used by the sampler,
         # this doesn't deep-copy LogitsProcessor objects
         sampling_params = sampling_params.clone()
-        # Add the eos token id into the sampling_params to support min_tokens
-        # processing
-        if seq.eos_token_id is not None:
-            sampling_params.all_stop_token_ids.add(seq.eos_token_id)
+
         sampling_params.update_from_generation_config(
-            self.generation_config_fields)
+            self.generation_config_fields, seq.eos_token_id)
 
         # Create the sequence group.
         seq_group = SequenceGroup(

vllm/sampling_params.py

@@ -280,17 +280,30 @@ def _verify_greedy_sampling(self) -> None:
                              f"Got {self.best_of}.")
 
     def update_from_generation_config(
-            self, generation_config: Dict[str, Any]) -> None:
+            self,
+            generation_config: Dict[str, Any],
+            model_eos_token_id: Optional[int] = None) -> None:
         """Update if there are non-default values from generation_config"""
+
+        if model_eos_token_id is not None:
+            # Add the eos token id into the sampling_params to support
+            # min_tokens processing.
+            self.all_stop_token_ids.add(model_eos_token_id)
+
         # Update eos_token_id for generation
-        if (not self.ignore_eos) and (eos_ids :=
-                                      generation_config.get("eos_token_id")):
+        if (eos_ids := generation_config.get("eos_token_id")) is not None:
             # it can be either int or list of int
-            if isinstance(eos_ids, int):
-                eos_ids = [eos_ids]
-            original_stop_token_ids = set(self.stop_token_ids)
-            original_stop_token_ids.update(eos_ids)
-            self.stop_token_ids = list(original_stop_token_ids)
+            eos_ids = {eos_ids} if isinstance(eos_ids, int) else set(eos_ids)
+            if model_eos_token_id is not None:
+                # We don't need to include the primary eos_token_id in
+                # stop_token_ids since it's handled separately for stopping
+                # purposes.
+                eos_ids.discard(model_eos_token_id)
+            if eos_ids:
+                self.all_stop_token_ids.update(eos_ids)
+                if not self.ignore_eos:
+                    eos_ids.update(self.stop_token_ids)
+                    self.stop_token_ids = list(eos_ids)
 
     @cached_property
     def sampling_type(self) -> SamplingType: