Support Cross encoder models (#10400)

Signed-off-by: Max de Bayser <maxdebayser@gmail.com>
Signed-off-by: Max de Bayser <mbayser@br.ibm.com>
Signed-off-by: Flavia Beo <flavia.beo@ibm.com>
Co-authored-by: Flavia Beo <flavia.beo@ibm.com>

vllm/transformers_utils/config.py

@@ -9,6 +9,7 @@ from huggingface_hub import (file_exists, hf_hub_download,
 from huggingface_hub.utils import (EntryNotFoundError, LocalEntryNotFoundError,
                                    RepositoryNotFoundError,
                                    RevisionNotFoundError)
+from torch import nn
 from transformers import GenerationConfig, PretrainedConfig
 from transformers.models.auto.image_processing_auto import (
     get_image_processor_config)
@@ -31,6 +32,7 @@ from vllm.transformers_utils.configs import (ChatGLMConfig, DbrxConfig,
                                              UltravoxConfig)
 # yapf: enable
 from vllm.transformers_utils.utils import check_gguf_file
+from vllm.utils import resolve_obj_by_qualname
 
 if VLLM_USE_MODELSCOPE:
     from modelscope import AutoConfig
@@ -577,3 +579,16 @@ def try_get_generation_config(
             return GenerationConfig.from_model_config(config)
         except OSError:  # Not found
             return None
+
+
+def get_cross_encoder_activation_function(config: PretrainedConfig):
+    if (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
+        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()