[Bugfix] Add use_cross_encoder flag to use correct activation in ClassifierPooler

vllm/entrypoints/llm.py

@@ -1204,7 +1204,7 @@ def _cross_encoding_score(
 
         input_pairs = [(t1, t2) for t1, t2 in zip(text_1, text_2)]
 
-        pooling_params = PoolingParams()
+        pooling_params = PoolingParams(use_cross_encoder=True)
 
         tokenization_kwargs: dict[str, Any] = {}
         _validate_truncation_size(self.llm_engine.model_config.max_model_len,

vllm/model_executor/layers/pooler.py

@@ -15,6 +15,7 @@
 from vllm.model_executor.pooling_metadata import PoolingTensors
 from vllm.sequence import PoolerOutput, PoolingSequenceGroupOutput
 from vllm.transformers_utils.config import (
+    get_classification_activation_function,
     get_cross_encoder_activation_function)
 from vllm.v1.pool.metadata import PoolingMetadata as V1PoolingMetadata
 
@@ -388,15 +389,14 @@ def __init__(
         self.classifier = classifier
         self.pooler = pooler
 
-        if config.task == "score":
-            self.default_activation_function = \
-                get_cross_encoder_activation_function(config.hf_config)
-        elif config.task == "classify":
-            self.default_activation_function = nn.Sigmoid() \
-                if config.hf_config.num_labels == 1 else nn.Softmax()
-        else:
-            raise NotImplementedError(f"task={config.task!r} is not supported"
-                                      " with the classification pooler")
+        self.classification_act_fn = get_classification_activation_function(
+            config.hf_config)
+        self.cross_encoder_act_fn = get_cross_encoder_activation_function(
+            config.hf_config)
+
+    def _get_act_fn(self, use_cross_encoder: bool):
+        return (self.cross_encoder_act_fn
+                if use_cross_encoder else self.classification_act_fn)
 
     def get_prompt_lens(
         self,
@@ -446,8 +446,29 @@ def forward(
             # apply classifier once on the full batch if possible
             pooled_output = self.classifier(pooled_output)
 
-        # shape: (batch_size, num_labels)
-        scores = self.default_activation_function(pooled_output)
+        if isinstance(pooling_metadata, V0PoolingMetadata):
+            use_cross_encoder_list = [
+                pooling_param.use_cross_encoder
+                for _, pooling_param in pooling_metadata.seq_groups
+            ]
+        else:
+            assert isinstance(pooled_data, list)
+            use_cross_encoder_list = [
+                pooling_param.use_cross_encoder
+                for pooling_param in pooling_metadata.pooling_params
+            ]
+
+        # shape of scores: (batch_size, num_labels)
+        if all(use_cross_encoder == use_cross_encoder_list[0]
+               for use_cross_encoder in use_cross_encoder_list):
+            act_fn = self._get_act_fn(use_cross_encoder_list[0])
+            scores = act_fn(pooled_output)
+        else:
+            scores = torch.stack([
+                self._get_act_fn(use_cross_encoder)(vecs)
+                for use_cross_encoder, vecs in zip(use_cross_encoder_list,
+                                                   pooled_data)
+            ])
 
         pooled_outputs = [PoolingSequenceGroupOutput(data) for data in scores]
         return PoolerOutput(outputs=pooled_outputs)

vllm/model_executor/models/bert.py

@@ -25,8 +25,6 @@
 from vllm.model_executor.model_loader.weight_utils import default_weight_loader
 from vllm.model_executor.pooling_metadata import PoolingMetadata
 from vllm.sequence import IntermediateTensors, PoolerOutput
-from vllm.transformers_utils.config import (
-    get_cross_encoder_activation_function)
 
 from .interfaces import SupportsCrossEncoding, SupportsQuant, SupportsV0Only
 from .utils import WeightsMapper, maybe_prefix
@@ -462,9 +460,6 @@ def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
         super().__init__()
         config = vllm_config.model_config.hf_config
 
-        self.default_activation_function = \
-            get_cross_encoder_activation_function(config)
-
         self.num_labels = config.num_labels
         self.bert = BertModel(vllm_config=vllm_config,
                               prefix=maybe_prefix(prefix, "bert"),

vllm/model_executor/models/roberta.py

@@ -18,8 +18,6 @@
 from vllm.model_executor.models.utils import WeightsMapper, maybe_prefix
 from vllm.model_executor.pooling_metadata import PoolingMetadata
 from vllm.sequence import IntermediateTensors, PoolerOutput
-from vllm.transformers_utils.config import (
-    get_cross_encoder_activation_function)
 
 from .bert_with_rope import BertWithRope, JinaRobertaModel
 from .interfaces import SupportsCrossEncoding, SupportsV0Only
@@ -178,9 +176,6 @@ def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
         super().__init__()
         config = vllm_config.model_config.hf_config
 
-        self.default_activation_function = \
-            get_cross_encoder_activation_function(config)
-
         self.num_labels = config.num_labels
         self.roberta = BertModel(vllm_config=vllm_config,
                                  prefix=maybe_prefix(prefix, "bert"),

vllm/pooling_params.py

@@ -24,12 +24,14 @@ class PoolingParams(
     """
 
     dimensions: Optional[int] = None
+    use_cross_encoder: bool = False
     additional_data: Optional[Any] = None
     output_kind: RequestOutputKind = RequestOutputKind.FINAL_ONLY
 
     def clone(self) -> "PoolingParams":
         """Returns a deep copy of the PoolingParams instance."""
         return PoolingParams(dimensions=self.dimensions,
+                             use_cross_encoder=self.use_cross_encoder,
                              additional_data=self.additional_data)
 
     def verify(self, model_config: "ModelConfig") -> None:
@@ -54,6 +56,7 @@ def verify(self, model_config: "ModelConfig") -> None:
     def __repr__(self) -> str:
         return (f"PoolingParams("
                 f"dimensions={self.dimensions}, "
+                f"use_cross_encoder={self.use_cross_encoder}, "
                 f"additional_metadata={self.additional_data})")
 
     def __post_init__(self) -> None:

vllm/transformers_utils/config.py

@@ -866,24 +866,26 @@ def try_get_generation_config(
             return None
 
 
-def get_cross_encoder_activation_function(config: PretrainedConfig):
+def get_classification_activation_function(config: PretrainedConfig):
+    return nn.Sigmoid() if config.num_labels == 1 else nn.Identity()
+
 
+def get_cross_encoder_activation_function(config: PretrainedConfig):
     function_name: Optional[str] = None
-    if hasattr(config, "sentence_transformers") and "activation_fn" in \
-        config.sentence_transformers:
+    if (hasattr(config, "sentence_transformers")
+            and "activation_fn" in config.sentence_transformers):
         function_name = config.sentence_transformers["activation_fn"]
-
     elif (hasattr(config, "sbert_ce_default_activation_function")
           and config.sbert_ce_default_activation_function is not None):
         function_name = config.sbert_ce_default_activation_function
 
     if function_name is not None:
-        assert function_name.startswith("torch.nn.modules."), \
-            "Loading of activation functions is restricted to " \
-            "torch.nn.modules for security reasons"
+        assert function_name.startswith("torch.nn.modules."), (
+            "Loading of activation functions is restricted to "
+            "torch.nn.modules for security reasons")
         return resolve_obj_by_qualname(function_name)()
-    else:
-        return nn.Sigmoid() if config.num_labels == 1 else nn.Identity()
+
+    return get_classification_activation_function(config)
 
 
 def try_get_safetensors_metadata(