[Model] Automatic conversion of classification and reward models

docs/source/models/supported_models.md

@@ -28,7 +28,7 @@ llm = LLM(model=..., task="generate")  # Name or path of your model
 output = llm.generate("Hello, my name is")
 print(output)
 
-# For pooling models (task={embed,classify,reward}) only
+# For pooling models (task={embed,classify,reward,score}) only
 llm = LLM(model=..., task="embed")  # Name or path of your model
 output = llm.encode("Hello, my name is")
 print(output)
@@ -59,7 +59,7 @@ llm = LLM(model=..., revision=..., task=..., trust_remote_code=True)
 output = llm.generate("Hello, my name is")
 print(output)
 
-# For pooling models (task={embed,classify,reward}) only
+# For pooling models (task={embed,classify,reward,score}) only
 output = llm.encode("Hello, my name is")
 print(output)
 ```
@@ -369,14 +369,6 @@ you should explicitly specify the task type to ensure that the model is used in
 
 #### Text Embedding (`--task embed`)
 
-Any text generation model can be converted into an embedding model by passing {code}`--task embed`.
-
-```{note}
-To get the best results, you should use pooling models that are specifically trained as such.
-```
-
-The following table lists those that are tested in vLLM.
-
 ```{eval-rst}
 .. list-table::
   :widths: 25 25 50 5 5
@@ -437,6 +429,10 @@ On the other hand, its 1.5B variant ({code}`Alibaba-NLP/gte-Qwen2-1.5B-instruct`
 despite being described otherwise on its model card.
 ```
 
+If your model is not in the above list, we will try to automatically convert the model using
+:func:`vllm.model_executor.models.adapters.as_embedding_model`. By default, the embeddings
+of the whole prompt are extracted from the normalized hidden state corresponding to the last token.
+
 #### Reward Modeling (`--task reward`)
 
 ```{eval-rst}
@@ -461,6 +457,9 @@ despite being described otherwise on its model card.
     - ✅︎
 ```
 
+If your model is not in the above list, we will try to automatically convert the model using
+:func:`vllm.model_executor.models.adapters.as_reward_model`. By default, we return the hidden states of each token directly.
+
 ```{important}
 For process-supervised reward models such as {code}`peiyi9979/math-shepherd-mistral-7b-prm`, the pooling config should be set explicitly,
 e.g.: {code}`--override-pooler-config '{"pooling_type": "STEP", "step_tag_id": 123, "returned_token_ids": [456, 789]}'`.
@@ -490,6 +489,9 @@ e.g.: {code}`--override-pooler-config '{"pooling_type": "STEP", "step_tag_id": 1
     - ✅︎
 ```
 
+If your model is not in the above list, we will try to automatically convert the model using
+:func:`vllm.model_executor.models.adapters.as_classification_model`. By default, the class probabilities are extracted from the softmaxed hidden state corresponding to the last token.
+
 #### Sentence Pair Scoring (`--task score`)
 
 ```{eval-rst}

tests/models/embedding/language/test_cls_models.py

@@ -1,7 +1,4 @@
-"""Compare the outputs of HF and vLLM when using greedy sampling.
-
-This test only tests small models. Big models such as 7B should be tested from
-test_big_models.py because it could use a larger instance to run tests.
+"""Compare the classification outputs of HF and vLLM models.
 
 Run `pytest tests/models/test_cls_models.py`.
 """

tests/models/embedding/language/test_scoring.py

@@ -1,6 +1,6 @@
-"""Compare the embedding outputs of HF and vLLM models.
+"""Compare the scoring outputs of HF and vLLM models.
 
-Run `pytest tests/models/embedding/language/test_embedding.py`.
+Run `pytest tests/models/embedding/language/test_scoring.py`.
 """
 import math
 

tests/models/test_registry.py

@@ -6,7 +6,9 @@
 from vllm.model_executor.models import (is_pooling_model,
                                         is_text_generation_model,
                                         supports_multimodal)
-from vllm.model_executor.models.adapters import as_embedding_model
+from vllm.model_executor.models.adapters import (as_classification_model,
+                                                 as_embedding_model,
+                                                 as_reward_model)
 from vllm.model_executor.models.registry import (_MULTIMODAL_MODELS,
                                                  _SPECULATIVE_DECODING_MODELS,
                                                  _TEXT_GENERATION_MODELS,
@@ -29,9 +31,10 @@ def test_registry_imports(model_arch):
             or model_arch in _MULTIMODAL_MODELS):
         assert is_text_generation_model(model_cls)
 
-    # All vLLM models should be convertible to an embedding model
-    embed_model = as_embedding_model(model_cls)
-    assert is_pooling_model(embed_model)
+    # All vLLM models should be convertible to a pooling model
+    assert is_pooling_model(as_classification_model(model_cls))
+    assert is_pooling_model(as_embedding_model(model_cls))
+    assert is_pooling_model(as_reward_model(model_cls))
 
     if model_arch in _MULTIMODAL_MODELS:
         assert supports_multimodal(model_cls)

vllm/model_executor/model_loader/utils.py

@@ -7,7 +7,9 @@
 
 from vllm.config import ModelConfig
 from vllm.model_executor.models import ModelRegistry
-from vllm.model_executor.models.adapters import as_embedding_model
+from vllm.model_executor.models.adapters import (as_classification_model,
+                                                 as_embedding_model,
+                                                 as_reward_model)
 
 
 @contextlib.contextmanager
@@ -35,8 +37,12 @@ def get_model_architecture(
         architectures = ["QuantMixtralForCausalLM"]
 
     model_cls, arch = ModelRegistry.resolve_model_cls(architectures)
-    if model_config.runner_type == "pooling":
+    if model_config.task == "embed":
         model_cls = as_embedding_model(model_cls)
+    elif model_config.task == "classify":
+        model_cls = as_classification_model(model_cls)
+    elif model_config.task == "reward":
+        model_cls = as_reward_model(model_cls)
 
     return model_cls, arch
 

vllm/model_executor/models/adapters.py

@@ -1,29 +1,48 @@
 from collections.abc import Iterable
-from typing import Any, TypeVar
+from typing import TYPE_CHECKING, Any, Optional, TypeVar
 
 import torch
 import torch.nn as nn
 
 from .interfaces_base import VllmModelForPooling, is_pooling_model
 
+if TYPE_CHECKING:
+    from vllm.model_executor.layers.pooler import PoolingType
+
 _T = TypeVar("_T", bound=type[nn.Module])
 
+_GENERATE_SUFFIXES = [
+    "ForCausalLM",
+    "ForConditionalGeneration",
+    "ChatModel",
+    "LMHeadModel",
+]
 
-def as_embedding_model(cls: _T) -> _T:
-    """Subclass an existing vLLM model to support embeddings."""
-    # Avoid modifying existing embedding models
-    if is_pooling_model(cls):
-        return cls
 
+def _get_pooling_model_name(orig_model_name: str, pooling_suffix: str) -> str:
+    model_name = orig_model_name
+
+    for generate_suffix in _GENERATE_SUFFIXES:
+        model_name = model_name.removesuffix(generate_suffix)
+
+    return model_name + pooling_suffix
+
+
+def _create_pooling_model_cls(
+    orig_cls: _T,
+    *,
+    default_pooling_type: "PoolingType",
+    default_normalize: bool,
+    default_softmax: bool,
+) -> _T:
     # Lazy import
     from vllm.config import VllmConfig
-    from vllm.model_executor.layers.pooler import (Pooler, PoolerOutput,
-                                                   PoolingType)
+    from vllm.model_executor.layers.pooler import Pooler, PoolerOutput
     from vllm.model_executor.pooling_metadata import PoolingMetadata
 
     from .utils import AutoWeightsLoader, WeightsMapper
 
-    class ModelForEmbedding(cls, VllmModelForPooling):
+    class ModelForPooling(orig_cls, VllmModelForPooling):
 
         def __init__(
             self,
@@ -34,7 +53,7 @@ def __init__(
         ) -> None:
             super().__init__(vllm_config=vllm_config, prefix=prefix, **kwargs)
 
-            # These are not used in embedding models
+            # These are not used in pooling models
             for attr in ("lm_head", "logits_processor"):
                 if hasattr(self, attr):
                     delattr(self, attr)
@@ -46,9 +65,9 @@ def __init__(
             if not getattr(self, "_pooler", None):
                 self._pooler = Pooler.from_config_with_defaults(
                     pooler_config,
-                    pooling_type=PoolingType.LAST,
-                    normalize=True,
-                    softmax=False,
+                    pooling_type=default_pooling_type,
+                    normalize=default_normalize,
+                    softmax=default_softmax,
                 )
 
         def pooler(
@@ -82,17 +101,148 @@ def load_weights(self, weights: Iterable[tuple[str, torch.Tensor]]):
                     return
 
             # For most other models
-            if hasattr(cls, "load_weights"):
-                cls.load_weights(self, weights)  # type: ignore
+            if hasattr(orig_cls, "load_weights"):
+                orig_cls.load_weights(self, weights)  # type: ignore
             # Fallback
             else:
                 loader = AutoWeightsLoader(self)
                 loader.load_weights(weights)
 
-    ModelForEmbedding.__name__ = cls.__name__ \
-        .removesuffix("ForCausalLM") \
-        .removesuffix("ForConditionalGeneration") \
-        .removesuffix("ChatModel") \
-        .removesuffix("LMHeadModel") + "ForEmbedding"
+    return ModelForPooling  # type: ignore
+
+
+def as_embedding_model(cls: _T) -> _T:
+    """
+    Subclass an existing vLLM model to support embeddings.
+
+    By default, the embeddings of the whole prompt are extracted from the
+    normalized hidden state corresponding to the last token.
+
+    Note:
+        We assume that no extra layers are added to the original model;
+        please implement your own model if this is not the case.
+    """
+    # Avoid modifying existing embedding models
+    if is_pooling_model(cls):
+        return cls
+
+    # Lazy import
+    from vllm.model_executor.layers.pooler import PoolingType
+
+    ModelForEmbedding = _create_pooling_model_cls(
+        cls,
+        default_pooling_type=PoolingType.LAST,
+        default_normalize=True,
+        default_softmax=False,
+    )
+    ModelForEmbedding.__name__ = \
+        _get_pooling_model_name(cls.__name__, "ForEmbedding")
 
     return ModelForEmbedding  # type: ignore
+
+
+def as_classification_model(cls: _T) -> _T:
+    """
+    Subclass an existing vLLM model to support classification.
+
+    By default, the class probabilities are extracted from the softmaxed
+    hidden state corresponding to the last token.
+
+    Note:
+        We assume that the classification head is a single linear layer
+        stored as the attribute `score` of the top-level model;
+        please implement your own model if this is not the case.
+    """
+    # Avoid modifying existing classification models
+    if is_pooling_model(cls):
+        return cls
+
+    # Lazy import
+    from vllm.attention import AttentionMetadata
+    from vllm.config import VllmConfig
+    from vllm.model_executor.layers.linear import RowParallelLinear
+    from vllm.model_executor.layers.pooler import PoolingType
+    from vllm.sequence import IntermediateTensors
+
+    from .utils import maybe_prefix
+
+    ModelForPooling = _create_pooling_model_cls(
+        cls,
+        default_pooling_type=PoolingType.LAST,
+        default_normalize=False,
+        default_softmax=True,
+    )
+
+    class ModelForClassification(ModelForPooling):
+
+        def __init__(
+            self,
+            *,
+            vllm_config: "VllmConfig",
+            prefix: str = "",
+            **kwargs: Any,
+        ) -> None:
+            super().__init__(vllm_config=vllm_config, prefix=prefix, **kwargs)
+
+            config = vllm_config.model_config.hf_config
+            quant_config = vllm_config.quant_config
+
+            self.score = RowParallelLinear(config.hidden_size,
+                                           config.num_labels,
+                                           quant_config=quant_config,
+                                           input_is_parallel=False,
+                                           bias=False,
+                                           prefix=maybe_prefix(
+                                               prefix, "score"))
+
+        def forward(
+            self,
+            input_ids: torch.Tensor,
+            positions: torch.Tensor,
+            kv_caches: list[torch.Tensor],
+            attn_metadata: AttentionMetadata,
+            intermediate_tensors: Optional[IntermediateTensors] = None,
+            inputs_embeds: Optional[torch.Tensor] = None,
+        ) -> torch.Tensor:
+            hidden_states = super().forward(input_ids, positions, kv_caches,
+                                            attn_metadata,
+                                            intermediate_tensors,
+                                            inputs_embeds)
+            logits, _ = self.score(hidden_states)
+            return logits
+
+
+    ModelForClassification.__name__ = \
+        _get_pooling_model_name(cls.__name__, "ForClassification")
+
+    return ModelForClassification  # type: ignore
+
+
+def as_reward_model(cls: _T) -> _T:
+    """
+    Subclass an existing vLLM model to support reward modeling.
+
+    By default, we return the hidden states of each token directly.
+
+    Note:
+        We assume that no extra layers are added to the original model;
+        please implement your own model if this is not the case.
+    """
+    # Avoid modifying existing reward models
+    if is_pooling_model(cls):
+        return cls
+
+    # Lazy import
+    from vllm.model_executor.layers.pooler import PoolingType
+
+    ModelForReward = _create_pooling_model_cls(
+        cls,
+        default_pooling_type=PoolingType.ALL,
+        default_normalize=False,
+        default_softmax=False,
+    )
+
+    ModelForReward.__name__ = \
+        _get_pooling_model_name(cls.__name__, "ForReward")
+
+    return ModelForReward  # type: ignore

vllm/model_executor/models/qwen2.py

@@ -545,8 +545,8 @@ def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
         self.model = Qwen2Model(vllm_config=vllm_config,
                                 prefix=maybe_prefix(prefix, "model"))
 
-        # TODO: Replace this model class with for_embedding(Qwen2ForCausalLM),
-        # after changing the default pooling method
+        # TODO: Replace this model class with as_embedding_model(
+        # Qwen2ForCausalLM) after changing the default pooling method
         if pooler_config.pooling_type is None:
             logger.warning(
                 "This embedding model will default to last-token pooling in "