[Core] Subclass ModelRunner to support cross-attention & encoder sequences...

[Core] Subclass ModelRunner to support cross-attention & encoder sequences (towards eventual encoder/decoder model support) (#4942)
Co-authored-by: Andrew Feldman <afeld2012@gmail.com>
Co-authored-by: Nick Hill <nickhill@us.ibm.com>

vllm/engine/arg_utils.py

@@ -69,7 +69,7 @@ class EngineArgs:
     rope_theta: Optional[float] = None
     tokenizer_revision: Optional[str] = None
     quantization: Optional[str] = None
-    enforce_eager: bool = False
+    enforce_eager: Optional[bool] = None
     max_context_len_to_capture: Optional[int] = None
     max_seq_len_to_capture: int = 8192
     disable_custom_all_reduce: bool = False

vllm/entrypoints/llm.py

@@ -121,12 +121,21 @@ class LLM:
         gpu_memory_utilization: float = 0.9,
         swap_space: int = 4,
         cpu_offload_gb: float = 0,
-        enforce_eager: bool = False,
+        enforce_eager: Optional[bool] = None,
         max_context_len_to_capture: Optional[int] = None,
         max_seq_len_to_capture: int = 8192,
         disable_custom_all_reduce: bool = False,
         **kwargs,
     ) -> None:
+        '''
+        LLM constructor.
+
+        Note: if enforce_eager is unset (enforce_eager is None)
+        it defaults to False for decoder-only models and True
+        for encoder/decoder models, since encoder/decoder models
+        do not currently support CUDAGraph.
+        '''
+
         if "disable_log_stats" not in kwargs:
             kwargs["disable_log_stats"] = True
         removed_vision_keys = ("image_token_id", "image_feature_size",
@@ -297,8 +306,8 @@ class LLM:
         """
         if self.llm_engine.model_config.embedding_mode:
             raise ValueError(
-                "LLM.generate() is only supported for generation models "
-                "(XForCausalLM).")
+                "LLM.generate() is only supported for (conditional) generation "
+                "models (XForCausalLM, XForConditionalGeneration).")
 
         if prompt_token_ids is not None:
             inputs = self._convert_v1_inputs(
@@ -631,3 +640,9 @@ class LLM:
         # This is necessary because some requests may be finished earlier than
         # its previous requests.
         return sorted(outputs, key=lambda x: int(x.request_id))
+
+    def _is_encoder_decoder_model(self):
+        return self.llm_engine.is_encoder_decoder_model()
+
+    def _is_embedding_model(self):
+        return self.llm_engine.is_embedding_model()

vllm/inputs/__init__.py

-from .data import (LLMInputs, ParsedText, ParsedTokens, PromptInputs,
-                   TextPrompt, TokensPrompt, parse_and_batch_prompt)
+from .data import (ExplicitEncoderDecoderPrompt, LLMInputs, ParsedText,
+                   ParsedTokens, PromptInputs, SingletonPromptInputs,
+                   TextPrompt, TokensPrompt, get_prompt_type,
+                   is_valid_encoder_decoder_llm_inputs, parse_and_batch_prompt)
 from .registry import InputContext, InputRegistry
 
 INPUT_REGISTRY = InputRegistry()
@@ -12,7 +14,18 @@ See also:
 """
 
 __all__ = [
-    "ParsedText", "ParsedTokens", "parse_and_batch_prompt", "TextPrompt",
-    "TokensPrompt", "PromptInputs", "LLMInputs", "INPUT_REGISTRY",
-    "InputContext", "InputRegistry"
+    "ParsedText",
+    "ParsedTokens",
+    "parse_and_batch_prompt",
+    "TextPrompt",
+    "TokensPrompt",
+    "PromptInputs",
+    "LLMInputs",
+    "INPUT_REGISTRY",
+    "InputContext",
+    "InputRegistry",
+    "get_prompt_type",
+    "is_valid_encoder_decoder_llm_inputs",
+    "ExplicitEncoderDecoderPrompt",
+    "SingletonPromptInputs",
 ]

vllm/inputs/data.py

@@ -92,15 +92,114 @@ class TokensPrompt(TypedDict):
     """
 
 
-PromptInputs = Union[str, TextPrompt, TokensPrompt]
+SingletonPromptInputs = Union[str, TextPrompt, TokensPrompt]
 """
-The inputs to the LLM, which can take one of the following forms:
+Set of possible schemas for a single LLM input:
 
 - A text prompt (:class:`str` or :class:`TextPrompt`)
 - A tokenized prompt (:class:`TokensPrompt`)
+
+Note that "singleton" is as opposed to a data structure
+which encapsulates multiple prompts, i.e. of the sort
+which may be utilized for encoder/decoder models when
+the user desires to express both the encoder & decoder
+prompts explicitly, i.e. ExplicitEncoderDecoderPrompt
+
+A prompt of type SingletonPromptInputs may be employed
+as (1) input to a decoder-only model, (2) input to
+the encoder of an encoder/decoder model, in the scenario
+where the decoder-prompt is not specified explicitly, or
+(3) as a member of a larger data structure encapsulating
+more than one prompt, i.e. ExplicitEncoderDecoderPrompt
 """
 
 
+class ExplicitEncoderDecoderPrompt(TypedDict):
+    """Represents an encoder/decoder model input prompt,
+    comprising an explicit encoder prompt and a 
+    decoder prompt.
+
+    The encoder and decoder prompts, respectively,
+    may formatted according to any of the
+    SingletonPromptInputs schemas, and are not
+    required to have the same schema.
+
+    Only the encoder prompt may have multi-modal data.
+
+    Note that an ExplicitEncoderDecoderPrompt may not
+    be used as an input to a decoder-only model,
+    and that the `encoder_prompt` and `decoder_prompt`
+    fields of this data structure may not themselves
+    must be SingletonPromptInputs instances.
+    """
+
+    encoder_prompt: SingletonPromptInputs
+
+    decoder_prompt: SingletonPromptInputs
+
+
+PromptInputs = Union[SingletonPromptInputs, ExplicitEncoderDecoderPrompt]
+"""
+Set of possible schemas for an LLM input, including
+both decoder-only and encoder/decoder input types:
+
+- A text prompt (:class:`str` or :class:`TextPrompt`)
+- A tokenized prompt (:class:`TokensPrompt`)
+- A single data structure containing both an encoder and a decoder prompt
+  (:class:`ExplicitEncoderDecoderPrompt`)
+"""
+
+
+def _has_required_keys(
+    d: dict,
+    required_keys: set,
+) -> bool:
+    return required_keys.issubset(d.keys())
+
+
+def get_prompt_type(prompt: Optional[PromptInputs]) -> Optional[str]:
+    """
+    Get the type-name of the prompt argument instance, given that
+    isinstance() cannot apply to TypedDict subclasses directly.
+    If the prompt is None, return 'None' as the type name.
+
+    Arguments:
+
+    * prompt: LLM input prompt or None
+
+    Returns:
+
+    * String representation of prompt type
+    """
+
+    if prompt is None:
+        return 'None'
+
+    required_keys_dict = {
+        'TextPrompt': {'prompt'},
+        'TokensPrompt': {'prompt_token_ids'},
+        'ExplicitEncoderDecoder': {'encoder_prompt', 'decoder_prompt'},
+    }
+
+    if isinstance(prompt, dict):
+        for (ptype, required_keys) in required_keys_dict.items():
+            # Ignore type checking in the conditional below because type
+            # checker does not understand that is_dict(prompt) narrows
+            # down the possible types
+            if _has_required_keys(
+                    prompt,  # type: ignore
+                    required_keys):
+                return ptype
+
+        raise ValueError(f"Invalid prompt {prompt}, valid types are "
+                         "required_keys_dict={required_keys_dict}")
+
+    if isinstance(prompt, str):
+        return "str"
+
+    raise ValueError(f"Invalid prompt {prompt}")
+
+
 class LLMInputs(TypedDict):
     """
     The inputs in :class:`~vllm.LLMEngine` before they are
@@ -114,8 +213,29 @@ class LLMInputs(TypedDict):
     The original prompt text corresponding to the token IDs, if available.
     """
 
+    encoder_prompt_token_ids: NotRequired[List[int]]
+    """The token IDs of the encoder prompt."""
+
+    encoder_prompt: NotRequired[Optional[str]]
+    """
+    The original encoder prompt text corresponding to the token IDs, if
+    available.
+    """
+
     multi_modal_data: NotRequired[Optional["MultiModalDataDict"]]
     """
     Optional multi-modal data to pass to the model,
     if the model supports it.
     """
+
+
+def is_valid_encoder_decoder_llm_inputs(inputs: LLMInputs) -> bool:
+    """
+    Return True if the LLMInputs instance has the correct configuration
+    for encoder/decoder.
+    """
+
+    # True if encoder prompt token ids field exists &
+    # is not None
+    return ('encoder_prompt_token_ids' in inputs
+            and inputs['encoder_prompt_token_ids'] is not None)

vllm/model_executor/models/__init__.py

@@ -83,7 +83,16 @@ _EMBEDDING_MODELS = {
     "MistralModel": ("llama_embedding", "LlamaEmbeddingModel"),
 }
 
-_MODELS = {**_GENERATION_MODELS, **_EMBEDDING_MODELS}
+_CONDITIONAL_GENERATION_MODELS = {
+    "BartModel": ("bart", "BartForConditionalGeneration"),
+    "BartForConditionalGeneration": ("bart", "BartForConditionalGeneration"),
+}
+
+_MODELS = {
+    **_GENERATION_MODELS,
+    **_EMBEDDING_MODELS,
+    **_CONDITIONAL_GENERATION_MODELS
+}
 
 # Architecture -> type.
 # out of tree models

vllm/outputs.py

@@ -70,12 +70,20 @@ class RequestOutput:
     Args:
         request_id: The unique ID of the request.
         prompt: The prompt string of the request.
+                For encoder/decoder models, this is the
+                decoder input prompt.
         prompt_token_ids: The token IDs of the prompt.
+                          For encoder/decoder models, this is the
+                          decoder input prompt token ids.
         prompt_logprobs: The log probabilities to return per prompt token.
         outputs: The output sequences of the request.
         finished: Whether the whole request is finished.
         metrics: Metrics associated with the request.
         lora_request: The LoRA request that was used to generate the output.
+        encoder_prompt: The encoder prompt string of the request; 
+                        None if decoder-only
+        encoder_prompt_token_ids: The token IDs of the encoder prompt;
+                                  None if decoder-only
     """
 
     def __init__(
@@ -88,6 +96,8 @@ class RequestOutput:
         finished: bool,
         metrics: Optional[RequestMetrics] = None,
         lora_request: Optional[LoRARequest] = None,
+        encoder_prompt: Optional[str] = None,
+        encoder_prompt_token_ids: Optional[List[int]] = None,
     ) -> None:
         self.request_id = request_id
         self.prompt = prompt
@@ -97,6 +107,8 @@ class RequestOutput:
         self.finished = finished
         self.metrics = metrics
         self.lora_request = lora_request
+        self.encoder_prompt = encoder_prompt
+        self.encoder_prompt_token_ids = encoder_prompt_token_ids
 
     @classmethod
     def from_seq_group(cls, seq_group: SequenceGroup) -> "RequestOutput":
@@ -137,6 +149,8 @@ class RequestOutput:
         # Every sequence in the sequence group should have the same prompt.
         prompt = seq_group.prompt
         prompt_token_ids = seq_group.prompt_token_ids
+        encoder_prompt = seq_group.encoder_prompt
+        encoder_prompt_token_ids = seq_group.encoder_prompt_token_ids
         prompt_logprobs = seq_group.prompt_logprobs
         finished = seq_group.is_finished()
         finished_time = time.time() if finished else None
@@ -148,12 +162,16 @@ class RequestOutput:
                    outputs,
                    finished,
                    seq_group.metrics,
-                   lora_request=seq_group.lora_request)
+                   lora_request=seq_group.lora_request,
+                   encoder_prompt=encoder_prompt,
+                   encoder_prompt_token_ids=encoder_prompt_token_ids)
 
     def __repr__(self) -> str:
         return (f"RequestOutput(request_id={self.request_id}, "
                 f"prompt={self.prompt!r}, "
                 f"prompt_token_ids={self.prompt_token_ids}, "
+                f"encoder_prompt={self.encoder_prompt!r}, "
+                f"encoder_prompt_token_ids={self.encoder_prompt_token_ids}, "
                 f"prompt_logprobs={self.prompt_logprobs}, "
                 f"outputs={self.outputs}, "
                 f"finished={self.finished}, "

vllm/sequence.py

@@ -7,10 +7,11 @@ from array import array
 from collections import defaultdict
 from dataclasses import dataclass, field
 from typing import (TYPE_CHECKING, Dict, List, Mapping, Optional, Set, Tuple,
-                    Union)
+                    Union, cast)
 
 import torch
 
+from vllm.inputs import is_valid_encoder_decoder_llm_inputs
 from vllm.lora.request import LoRARequest
 from vllm.pooling_params import PoolingParams
 from vllm.prompt_adapter.request import PromptAdapterRequest
@@ -244,13 +245,26 @@ class SequenceData:
 class Sequence:
     """Stores the data, status, and block information of a sequence.
 
+    The sequence is constructed from the LLMInputs instance passed
+    in through the `inputs` constructor argument.
+
+    For encoder/decoder models, LLMInputs encapsulates both a
+    decoder and encoder prompt, creating an ambiguity about which
+    prompt to construct the sequence from. The `from_decoder_prompt`
+    constructor argument signals whether to construct the Sequence
+    from the LLMInputs decoder prompt, or encoder prompt.
+
     Args:
         seq_id: The ID of the sequence.
         inputs: The inputs of the sequence.
         block_size: The block size of the sequence. Should be the same as the
             block size used by the block manager and cache engine.
+        eos_token_id: The end-of-sequence (EOS) token id recognized by this LLM.
         lora_request: LoRA request.
         prompt_adapter_request: Prompt Adapter request.
+        from_decoder_prompt: Construct Sequence from LLMInputs decoder prompt
+                             (True) or encoder prompt (False.) Must be True
+                             for decoder-only model.
 
     """
 
@@ -261,7 +275,8 @@ class Sequence:
         block_size: int,
         eos_token_id: Optional[int] = None,
         lora_request: Optional[LoRARequest] = None,
-            prompt_adapter_request: Optional[PromptAdapterRequest] = None
+        prompt_adapter_request: Optional[PromptAdapterRequest] = None,
+        from_decoder_prompt: bool = True,
     ) -> None:
         self.seq_id = seq_id
         self.inputs = inputs
@@ -269,6 +284,36 @@ class Sequence:
         self.eos_token_id = eos_token_id
         self.lora_request = lora_request
         self.prompt_adapter_request = prompt_adapter_request
+        self.from_decoder_prompt = from_decoder_prompt
+        self._prompt: Optional[str] = None
+        self._prompt_token_ids: Optional[List[int]] = None
+
+        # For decoder-only models, a Sequence is constructed
+        # from an LLMInputs instance (the `inputs` arg.)
+        #
+        # For encoder/decoder models the same `inputs`
+        # instance could be utilized to construct either an
+        # encoder sequence or a decoder sequence, because
+        # `LLMInputs` has both decoder- and encoder-oriented
+        # member variables (i.e. it encapsulates both an encoder
+        # and a decoder prompt.) The decision of which type of sequence
+        # to generate is determined by the `from_decoder_prompt` argument.
+        #
+        # When constructing a encoder sequence
+        # (`from_decoder_prompt` False) it matters that
+        # the `LLMInputs` instance stored in `inputs` is valid
+        # in the sense that its encoder-related member variables are
+        # populated; below, an exception is raised if this is
+        # not the case.
+        #
+        # When constructing a decoder sequence (`from_decoder_prompt` True)
+        # it does not matter whether `inputs` has its encoder-related
+        # member variables populated.
+        if not (from_decoder_prompt
+                or is_valid_encoder_decoder_llm_inputs(inputs)):
+            raise ValueError("Cannot extract encoder input prompt from "
+                             f"invalid input {inputs}; did you forget the "
+                             "encoder input prompt fields?")
 
         self.data = SequenceData(self.prompt_token_ids)
         self.output_logprobs: SampleLogprobs = []
@@ -289,11 +334,35 @@ class Sequence:
 
     @property
     def prompt(self) -> Optional[str]:
-        return self.inputs.get("prompt")
+        if self._prompt is not None:
+            # Reuse precomputed prompt string
+            return self._prompt
+
+        # Select decoder or encoder input prompt str,
+        # as appropriate
+        prompt_key: str = ("prompt"
+                           if self.from_decoder_prompt else "encoder_prompt")
+
+        # Cache prompt
+        self._prompt = cast(Optional[str], self.inputs.get(prompt_key))
+        return self._prompt
 
     @property
     def prompt_token_ids(self) -> List[int]:
-        return self.inputs["prompt_token_ids"]
+        if self._prompt_token_ids is not None:
+            # Reuse precomputed prompt token ids
+            return self._prompt_token_ids
+
+        # Select decoder or encoder input prompt
+        # token ids, as appropriate
+        prompt_token_ids_key: str = ("prompt_token_ids"
+                                     if self.from_decoder_prompt else
+                                     "encoder_prompt_token_ids")
+
+        # Cache computed prompt token ids
+        self._prompt_token_ids = cast(List[int],
+                                      self.inputs.get(prompt_token_ids_key))
+        return self._prompt_token_ids
 
     @property
     def multi_modal_data(self) -> "MultiModalDataDict":
@@ -472,6 +541,22 @@ class SequenceGroup:
         # We use the prompt of an arbitrary sequence.
         return self.seqs[0].prompt_token_ids
 
+    @property
+    def encoder_prompt(self) -> Optional[str]:
+        # There are either 0 or 1 encoder sequences
+        # If one is present, its prompt is distinct
+        # from the decoder's.
+        return (self.encoder_seq.prompt
+                if self.encoder_seq is not None else None)
+
+    @property
+    def encoder_prompt_token_ids(self) -> Optional[List[int]]:
+        # There are either 0 or 1 encoder sequences
+        # If one is present, its prompt token ids are
+        # distinct from the decoder's.
+        return (self.encoder_seq.prompt_token_ids
+                if self.encoder_seq is not None else None)
+
     @property
     def multi_modal_data(self) -> "MultiModalDataDict":
         # All sequences in the group should have the same multi-modal data.

vllm/utils.py

@@ -27,10 +27,93 @@ from typing_extensions import ParamSpec
 
 import vllm.envs as envs
 from vllm import _custom_ops as ops
+from vllm.inputs import (ExplicitEncoderDecoderPrompt, PromptInputs,
+                         SingletonPromptInputs)
 from vllm.logger import enable_trace_function_call, init_logger
 
 logger = init_logger(__name__)
 
+# Exception strings for non-implemented encoder/decoder scenarios
+
+STR_NOT_IMPL_ENC_DEC_SWA = \
+    "Sliding window attention for encoder/decoder models " + \
+                    "is not currently supported."
+
+STR_NOT_IMPL_ENC_DEC_PREFIX_CACHE = \
+    "Prefix caching for encoder/decoder models " + \
+                    "is not currently supported."
+
+STR_NOT_IMPL_ENC_DEC_CHUNKED_PREFILL = \
+    "Chunked prefill for encoder/decoder models " + \
+                    "is not currently supported."
+
+STR_NOT_IMPL_ENC_DEC_LOGIT_SOFTCAP = (
+    "Models with logits_soft_cap "
+    "require FlashInfer backend, which is "
+    "currently not supported for encoder/decoder "
+    "models.")
+
+STR_NOT_IMPL_ENC_DEC_LORA = ("LoRA is currently not currently "
+                             "supported with encoder/decoder "
+                             "models.")
+
+STR_NOT_IMPL_ENC_DEC_PP = ("Pipeline parallelism is not "
+                           "currently supported with "
+                           "encoder/decoder models.")
+
+STR_NOT_IMPL_ENC_DEC_MM = ("Multimodal is not currently "
+                           "supported with encoder/decoder "
+                           "models.")
+
+STR_NOT_IMPL_ENC_DEC_SPEC_DEC = ("Speculative decoding is not "
+                                 "currently supported with encoder/"
+                                 "decoder models.")
+
+STR_NOT_IMPL_ENC_DEC_CUDAGRAPH = ("CUDAGraph is not "
+                                  "currently supported with encoder/"
+                                  "decoder models.")
+
+STR_NOT_IMPL_ENC_DEC_BACKEND = ("XFormers is the only backend "
+                                "currently supported with encoder/"
+                                "decoder models.")
+
+STR_NOT_IMPL_ENC_DEC_PROMPT_ADAPTER = ("Prompt adapters are not "
+                                       "currently supported with encoder/"
+                                       "decoder models.")
+
+# Efficiently import all enc/dec error strings
+# rather than having to import all of the above
+STR_NOT_IMPL_ENC_DEC_ERR_STRS = {
+    "STR_NOT_IMPL_ENC_DEC_SWA": STR_NOT_IMPL_ENC_DEC_SWA,
+    "STR_NOT_IMPL_ENC_DEC_PREFIX_CACHE": STR_NOT_IMPL_ENC_DEC_PREFIX_CACHE,
+    "STR_NOT_IMPL_ENC_DEC_CHUNKED_PREFILL":
+    STR_NOT_IMPL_ENC_DEC_CHUNKED_PREFILL,
+    "STR_NOT_IMPL_ENC_DEC_LOGIT_SOFTCAP": STR_NOT_IMPL_ENC_DEC_LOGIT_SOFTCAP,
+    "STR_NOT_IMPL_ENC_DEC_LORA": STR_NOT_IMPL_ENC_DEC_LORA,
+    "STR_NOT_IMPL_ENC_DEC_PP": STR_NOT_IMPL_ENC_DEC_PP,
+    "STR_NOT_IMPL_ENC_DEC_MM": STR_NOT_IMPL_ENC_DEC_MM,
+    "STR_NOT_IMPL_ENC_DEC_SPEC_DEC": STR_NOT_IMPL_ENC_DEC_SPEC_DEC,
+    "STR_NOT_IMPL_ENC_DEC_CUDA_GRAPH": STR_NOT_IMPL_ENC_DEC_CUDAGRAPH,
+    "STR_NOT_IMPL_ENC_DEC_BACKEND": STR_NOT_IMPL_ENC_DEC_BACKEND,
+    "STR_NOT_IMPL_ENC_DEC_PROMPT_ADAPTER": STR_NOT_IMPL_ENC_DEC_PROMPT_ADAPTER,
+}
+
+# Constants related to forcing the attention backend selection
+
+# String name of register which may be set in order to
+# force auto-selection of attention backend by Attention
+# wrapper
+STR_BACKEND_ENV_VAR: str = "VLLM_ATTENTION_BACKEND"
+
+# Possible string values of STR_BACKEND_ENV_VAR
+# register, corresponding to possible backends
+STR_FLASHINFER_ATTN_VAL: str = "FLASHINFER"
+STR_TORCH_SDPA_ATTN_VAL: str = "TORCH_SDPA"
+STR_ROCM_FLASH_ATTN_VAL: str = "ROCM_FLASH"
+STR_XFORMERS_ATTN_VAL: str = "XFORMERS"
+STR_FLASH_ATTN_VAL: str = "FLASH_ATTN"
+STR_INVALID_VAL: str = "INVALID"
+
 STR_DTYPE_TO_TORCH_DTYPE = {
     "half": torch.half,
     "bfloat16": torch.bfloat16,
@@ -1029,3 +1112,50 @@ async def _run_task_with_lock(task: Callable, lock: asyncio.Lock, *args,
     """Utility function to run async task in a lock"""
     async with lock:
         return await task(*args, **kwargs)
+
+
+def is_encoder_decoder_model_config(model_config) -> bool:
+    '''
+    Extract the HF encoder/decoder model flag from the ModelConfig instance.
+    Return False if model_config is None.
+    '''
+    return model_config is not None and \
+                getattr(model_config.hf_config,
+                        "is_encoder_decoder",
+                        False)
+
+
+def is_embedding_model_config(model_config) -> bool:
+    '''
+    Extract the embedding model flag from the ModelConfig instance.
+    Return False if model_config is None.
+    '''
+    return model_config is not None and \
+                model_config.embedding_mode
+
+
+def build_explicit_enc_dec_prompt(
+    encoder_prompt: SingletonPromptInputs,
+    decoder_prompt: SingletonPromptInputs,
+) -> ExplicitEncoderDecoderPrompt:
+    return ExplicitEncoderDecoderPrompt(encoder_prompt=encoder_prompt,
+                                        decoder_prompt=decoder_prompt)
+
+
+def zip_enc_dec_prompt_lists(
+    enc_prompt_list: List[SingletonPromptInputs],
+    dec_prompt_list: List[SingletonPromptInputs],
+) -> List[ExplicitEncoderDecoderPrompt]:
+    return [
+        build_explicit_enc_dec_prompt(encoder_prompt, decoder_prompt)
+        for (encoder_prompt,
+             decoder_prompt) in zip(enc_prompt_list, dec_prompt_list)
+    ]
+
+
+def to_enc_dec_tuple_list(
+    enc_dec_prompts: List[ExplicitEncoderDecoderPrompt],
+) -> List[Tuple[PromptInputs, PromptInputs]]:
+    return [(enc_dec_prompt['encoder_prompt'],
+             enc_dec_prompt['decoder_prompt'])
+            for enc_dec_prompt in enc_dec_prompts]

vllm/worker/enc_dec_model_runner.py

+import dataclasses
+from typing import Any, Dict, List, Optional, Tuple, Type, cast
+
+import torch
+import torch.distributed
+
+from vllm.attention.backends.abstract import (AttentionBackend,
+                                              AttentionMetadata)
+from vllm.attention.selector import (_Backend, get_env_variable_attn_backend,
+                                     get_global_forced_attn_backend,
+                                     global_force_attn_backend)
+from vllm.config import (CacheConfig, DeviceConfig, LoadConfig, LoRAConfig,
+                         ModelConfig, MultiModalConfig, ParallelConfig,
+                         PromptAdapterConfig, SchedulerConfig)
+from vllm.inputs import INPUT_REGISTRY
+from vllm.logger import init_logger
+from vllm.model_executor import SamplingMetadata
+from vllm.sampling_params import SamplingParams
+from vllm.sequence import (IntermediateTensors, PoolerOutput, SamplerOutput,
+                           SequenceGroupMetadata)
+from vllm.utils import STR_NOT_IMPL_ENC_DEC_BACKEND, make_tensor_with_pad
+from vllm.worker.model_runner import (_PAD_SLOT_ID, GPUModelRunnerBase,
+                                      ModelInputForGPUBuilder,
+                                      ModelInputForGPUWithSamplingMetadata)
+from vllm.worker.model_runner_base import (
+    _add_attn_metadata_broadcastable_dict,
+    _add_sampling_metadata_broadcastable_dict)
+from vllm.worker.utils import assert_enc_dec_mr_supported_scenario
+
+logger = init_logger(__name__)
+
+
+@dataclasses.dataclass(frozen=True)
+class EncoderDecoderModelInput(ModelInputForGPUWithSamplingMetadata):
+    """
+    Used by the EncoderDecoderModelRunner.
+    """
+    encoder_input_tokens: Optional[torch.Tensor] = None
+    encoder_input_positions: Optional[torch.Tensor] = None
+
+    def as_broadcastable_tensor_dict(self) -> Dict[str, Any]:
+        tensor_dict = {
+            "input_tokens": self.input_tokens,
+            "input_positions": self.input_positions,
+            "encoder_input_tokens": self.encoder_input_tokens,
+            "encoder_input_positions": self.encoder_input_positions,
+            "virtual_engine": self.virtual_engine,
+            "request_ids_to_seq_ids": self.request_ids_to_seq_ids,
+            "finished_requests_ids": self.finished_requests_ids,
+        }
+        _add_attn_metadata_broadcastable_dict(tensor_dict, self.attn_metadata)
+        _add_sampling_metadata_broadcastable_dict(tensor_dict,
+                                                  self.sampling_metadata)
+        return tensor_dict
+
+    @classmethod
+    def from_broadcasted_tensor_dict(
+        cls,
+        tensor_dict: Dict[str, Any],
+        attn_backend: Optional["AttentionBackend"] = None,
+    ) -> "EncoderDecoderModelInput":
+        return cast(
+            EncoderDecoderModelInput,
+            super().from_broadcasted_tensor_dict(tensor_dict, attn_backend))
+
+
+class EncoderDecoderModelRunner(GPUModelRunnerBase[EncoderDecoderModelInput]):
+    _model_input_cls: Type[EncoderDecoderModelInput] = (
+        EncoderDecoderModelInput)
+    _builder_cls: Type[ModelInputForGPUBuilder] = (ModelInputForGPUBuilder)
+
+    def __init__(
+        self,
+        model_config: ModelConfig,
+        parallel_config: ParallelConfig,
+        scheduler_config: SchedulerConfig,
+        device_config: DeviceConfig,
+        cache_config: CacheConfig,
+        load_config: LoadConfig,
+        lora_config: Optional[LoRAConfig],
+        kv_cache_dtype: Optional[str] = "auto",
+        is_driver_worker: bool = False,
+        prompt_adapter_config: Optional[PromptAdapterConfig] = None,
+        multimodal_config: Optional[MultiModalConfig] = None,
+    ):
+        '''
+        EncoderDecoderModelRunner constructor.
+
+        `lora_config`, `multimodal_config`, and prompt_adapter_config are
+        unused (since these features are not yet supported for encoder/decoder
+        models) but these arguments are present here for compatibility with 
+        the base-class constructor.
+        '''
+
+        self._maybe_force_supported_attention_backend()
+
+        super().__init__(
+            model_config,
+            parallel_config,
+            scheduler_config,
+            device_config,
+            cache_config,
+            load_config,
+            lora_config=None,
+            kv_cache_dtype=kv_cache_dtype,
+            is_driver_worker=is_driver_worker,
+        )
+
+        # Crash for unsupported encoder/scenarios
+        assert_enc_dec_mr_supported_scenario(self)
+
+    def _maybe_force_supported_attention_backend(self):
+        '''
+        Force vLLM to use the XFormers attention backend,
+        which is currently the only supported option.
+        '''
+
+        def raise_backend_err():
+            # The user has specified an attention backend override
+            # which is invalid for encoder/decoder models
+            raise NotImplementedError(STR_NOT_IMPL_ENC_DEC_BACKEND)
+
+        maybe_env_var_forced_backend = get_env_variable_attn_backend()
+        maybe_global_forced_backend = get_global_forced_attn_backend()
+        is_forced_by_global = maybe_global_forced_backend is not None
+        is_forced_by_env_var = maybe_env_var_forced_backend is not None
+
+        if not (is_forced_by_global or is_forced_by_env_var):
+            # The user has not already specified an attention backend
+            # override
+            logger.info("EncoderDecoderModelRunner requires "
+                        "XFormers backend; overriding backend "
+                        "auto-selection and forcing XFormers.")
+            global_force_attn_backend(_Backend.XFORMERS)
+        elif is_forced_by_global:
+            # Backend override enforced by global variable takes
+            # precedence over vLLM backend environment variable.
+            if maybe_global_forced_backend != _Backend.XFORMERS:
+                raise_backend_err()
+        elif is_forced_by_env_var:
+            # Backend override enforced by vLLM backend
+            # environment variable
+            if maybe_env_var_forced_backend != _Backend.XFORMERS:
+                raise_backend_err()
+
+    def _list_to_int32_tensor(
+        self,
+        _list: List[int],
+    ) -> torch.Tensor:
+        return torch.tensor(_list, dtype=torch.int32, device=self.device)
+
+    def _list_to_long_tensor(
+        self,
+        _list: List[int],
+    ) -> torch.Tensor:
+        return torch.tensor(_list, dtype=torch.long, device=self.device)
+
+    def _empty_int32_tensor(self) -> torch.Tensor:
+        return self._list_to_int32_tensor([])
+
+    def _empty_long_tensor(self) -> torch.Tensor:
+        return self._list_to_long_tensor([])
+
+    @torch.inference_mode()
+    def execute_model(
+        self,
+        model_input: EncoderDecoderModelInput,
+        kv_caches: List[torch.Tensor],
+        intermediate_tensors: Optional[IntermediateTensors] = None,
+        num_steps: int = 1,
+    ) -> Optional[List[PoolerOutput]]:
+        if num_steps > 1:
+            raise ValueError("num_steps > 1 is not supported in "
+                             "EncoderDecoderModelRunner")
+
+        model_executable = self.model
+
+        seqlen_agnostic_kwargs = {
+            "finished_requests_ids": model_input.finished_requests_ids,
+            "request_ids_to_seq_ids": model_input.request_ids_to_seq_ids,
+        } if self.has_seqlen_agnostic else {}
+        hidden_or_intermediate_states = model_executable(
+            input_ids=model_input.input_tokens,
+            positions=model_input.input_positions,
+            encoder_input_ids=model_input.encoder_input_tokens,
+            encoder_positions=model_input.encoder_input_positions,
+            kv_caches=kv_caches,
+            attn_metadata=model_input.attn_metadata,
+            intermediate_tensors=intermediate_tensors,
+            **seqlen_agnostic_kwargs)
+
+        logits = self.model.compute_logits(hidden_or_intermediate_states,
+                                           model_input.sampling_metadata)
+
+        if not self.is_driver_worker:
+            return []
+
+        # Sample the next token.
+        output: SamplerOutput = self.model.sample(
+            logits=logits,
+            sampling_metadata=model_input.sampling_metadata,
+        )
+
+        return [output]
+
+    def make_model_input_from_broadcasted_tensor_dict(
+            self, tensor_dict: Dict[str, Any]) -> EncoderDecoderModelInput:
+        return EncoderDecoderModelInput.from_broadcasted_tensor_dict(
+            tensor_dict,
+            attn_backend=self.attn_backend,
+        )
+
+    def prepare_model_input(
+        self,
+        seq_group_metadata_list: List[SequenceGroupMetadata],
+        virtual_engine: int = 0,
+        finished_requests_ids: Optional[List[str]] = None
+    ) -> EncoderDecoderModelInput:
+        """Prepare the model input based on a given sequence group, including
+        metadata for the sampling step.
+
+        Since chunked prefill is not supported for encoder/decoder models,
+        `input_tokens` is assumed to be either entirely prefill tokens or
+        entirely decode tokens.
+
+        """
+        model_input = self._prepare_model_input_tensors(
+            seq_group_metadata_list, finished_requests_ids)
+
+        (
+            attn_metadata,
+            encoder_input_tokens_tensor,
+            encoder_input_positions_tensor,
+        ) = (self._prepare_encoder_model_input_tensors(seq_group_metadata_list,
+                                                       model_input))
+
+        # Inject attn_metadata encoder/cross-attention fields &
+        # encoder input tokens/positions into model_input.
+        # Frozen dataclass fields cannot be modified, so use
+        # dataclasses.replace to construct a new model input
+        # instance.
+        model_input = dataclasses.replace(
+            model_input,
+            attn_metadata=attn_metadata,
+            encoder_input_tokens=encoder_input_tokens_tensor,
+            encoder_input_positions=encoder_input_positions_tensor,
+        )
+
+        sampling_metadata = SamplingMetadata.prepare(seq_group_metadata_list,
+                                                     model_input.seq_lens,
+                                                     model_input.query_lens,
+                                                     self.device,
+                                                     self.pin_memory)
+        is_prompt = (seq_group_metadata_list[0].is_prompt
+                     if seq_group_metadata_list else None)
+        return dataclasses.replace(model_input,
+                                   sampling_metadata=sampling_metadata,
+                                   is_prompt=is_prompt,
+                                   virtual_engine=virtual_engine)
+
+    @torch.inference_mode()
+    def profile_run(self) -> None:
+        # Enable top-k sampling to reflect the accurate memory usage.
+        sampling_params = SamplingParams(top_p=0.99, top_k=self.vocab_size - 1)
+        max_num_batched_tokens = self.scheduler_config.max_num_batched_tokens
+        max_num_seqs = self.scheduler_config.max_num_seqs
+
+        # Profile memory usage with max_num_sequences sequences and the total
+        # number of tokens equal to max_num_batched_tokens.
+        seqs: List[SequenceGroupMetadata] = []
+
+        model_config = self.model_config
+
+        batch_size = 0
+        for group_id in range(max_num_seqs):
+            seq_len = (max_num_batched_tokens // max_num_seqs +
+                       (group_id < max_num_batched_tokens % max_num_seqs))
+            batch_size += seq_len
+
+            seq_data, _ = INPUT_REGISTRY \
+                .dummy_data_for_profiling(model_config, seq_len)
+
+            # Having more tokens is over-conservative but otherwise fine
+            assert len(seq_data.prompt_token_ids) >= seq_len, (
+                f"Expected at least {seq_len} dummy tokens for profiling, "
+                f"but got: {len(seq_data.prompt_token_ids)}")
+
+            seq = SequenceGroupMetadata(
+                request_id=str(group_id),
+                is_prompt=True,
+                seq_data={group_id: seq_data},
+                sampling_params=sampling_params,
+                block_tables=None,
+                encoder_seq_data=seq_data,
+                cross_block_table=None,
+            )
+            seqs.append(seq)
+
+        # Run the model with the dummy inputs.
+        num_layers = self.model_config.get_num_layers(self.parallel_config)
+        kv_caches = [None] * num_layers
+        finished_requests_ids = [seq.request_id for seq in seqs]
+        model_input = self.prepare_model_input(
+            seqs, finished_requests_ids=finished_requests_ids)
+        intermediate_tensors = None
+        self.execute_model(model_input, kv_caches, intermediate_tensors)
+        torch.cuda.synchronize()
+        return
+
+    def _prepare_encoder_model_input_tensors(
+        self,
+        seq_group_metadata_list: List[SequenceGroupMetadata],
+        model_input: EncoderDecoderModelInput,
+    ) -> Tuple[AttentionMetadata, Optional[torch.Tensor],
+               Optional[torch.Tensor]]:
+        """Helper method to prepare the encoder- and cross-attn-related
+        model inputs based on a given sequence group. These additional inputs
+        are used to augment an already-computed `EncoderDecoderModelInput`
+        data structure which already has decoder-related model inputs
+        populated.
+
+        Sets the following attn_metadata fields:
+        * `num_encoder_tokens`
+        * `encoder_seq_lens`
+        * `encoder_seq_lens_tensor`
+        * `max_encoder_seq_len`
+        * `cross_slot_mapping`
+        * `cross_block_tables`
+
+        Constructs a new model inputs data structure, based on
+        (1) the existing fields in the `model_inputs` argument,
+        and (2) the following additional fields which are
+        computed (or in the case of `attn_metadata`, updated) 
+        by this function:
+        * attn_metadata
+        * encoder_input_tokens
+        * encoder_input_positions
+
+        Arguments:
+
+        * seq_group_metadata_list: list of sequence groups for which to
+                                   compute inputs
+        * model_inputs: model inputs data structure with decoder-oriented
+                        fields already computed.
+
+        Return:
+
+        * Updated model inputs data structure
+        """
+
+        if len(seq_group_metadata_list) == 0:
+            return (model_input.attn_metadata, None, None)
+
+        # Since we are not supporting chunked prefill either the entire
+        # batch is prefill or it is decode
+        is_prompt = seq_group_metadata_list[0].is_prompt
+
+        # Build encoder inputs
+        encoder_seq_lens: List[int] = []
+        if is_prompt:
+            # Prefill phase.
+            cross_block_tables = self._empty_int32_tensor().view(
+                len(seq_group_metadata_list), -1)
+
+            # Extract input tokens/positions, cross-attention slot-mapping,
+            # & seq len from each sequence group metadata
+            (
+                encoder_input_tokens,
+                encoder_input_positions,
+                cross_slot_mapping,
+            ) = (
+                [],
+                [],
+                [],
+            )
+            for seq_group_metadata in seq_group_metadata_list:
+                # Build seq lens
+                seq_len = seq_group_metadata.encoder_seq_data.get_len()
+                token_ids = seq_group_metadata.encoder_seq_data.get_token_ids()
+                encoder_seq_lens.append(seq_len)
+
+                # Build slot mapping
+                is_profile_run = (seq_group_metadata.block_tables is None)
+                if is_profile_run:
+                    # During memory profiling, the block tables are not
+                    # initialized yet. In this case, we just use a dummy
+                    # slot mapping.
+                    # In embeddings, the block tables are {seq_id: None}.
+                    cross_slot_mapping.extend([_PAD_SLOT_ID] * seq_len)
+                else:
+                    for i in range(0, seq_len):
+                        block_number = seq_group_metadata.cross_block_table[
+                            i // self.block_size]
+                        block_offset = i % self.block_size
+                        slot = block_number * self.block_size + block_offset
+                        cross_slot_mapping.append(slot)
+
+                # Build encoder input tokens
+                encoder_input_tokens.extend(token_ids)
+                encoder_input_positions.extend(list(range(0, seq_len)))
+
+            # Convert tokens/positions & cross-attention
+            # slot-mapping to encoder input tensors
+            encoder_input_tokens_tensor = self._list_to_long_tensor(
+                encoder_input_tokens)
+            encoder_input_positions_tensor = self._list_to_long_tensor(
+                encoder_input_positions)
+            cross_slot_mapping_tensor = self._list_to_long_tensor(
+                cross_slot_mapping)
+
+        else:
+            # Decode phase.
+            encoder_input_tokens_tensor = self._empty_long_tensor()
+            encoder_input_positions_tensor = self._empty_long_tensor()
+            cross_slot_mapping_tensor = self._empty_long_tensor()
+
+            # Extract cross-attention block tables &
+            # seq len from each sequence group metadata.
+            # Cross-attention block tables are empty
+            # during vLLM memory profiling.
+            cross_block_tables = []
+            for seq_group_metadata in seq_group_metadata_list:
+                encoder_seq_lens.append(
+                    seq_group_metadata.encoder_seq_data.get_len())
+                cross_block_table = seq_group_metadata.cross_block_table
+                cross_block_tables.append([] if (
+                    cross_block_table is None) else cross_block_table)
+
+            # Convert cross-attention block tables to encoder input tensor
+            cross_block_tables = make_tensor_with_pad(
+                cross_block_tables,
+                max_len=max(
+                    len(block_table) for block_table in cross_block_tables),
+                pad=0,
+                dtype=torch.int32,
+                device=self.device,
+            )
+
+        # Compute encoder sequence lengths & encoder
+        # sequence starting offset tensors
+        max_encoder_seq_len = max(encoder_seq_lens, default=0)
+        encoder_seq_lens_tensor = self._list_to_int32_tensor(encoder_seq_lens)
+        encoder_seq_start_loc = torch.zeros(encoder_seq_lens_tensor.shape[0] +
+                                            1,
+                                            dtype=torch.int32,
+                                            device=self.device)
+        torch.cumsum(encoder_seq_lens_tensor,
+                     dim=0,
+                     dtype=encoder_seq_start_loc.dtype,
+                     out=encoder_seq_start_loc[1:])
+
+        # Update attention metadata with encoder-oriented attributes
+        attn_metadata = model_input.attn_metadata
+        assert attn_metadata is not None
+        (
+            attn_metadata.num_encoder_tokens,
+            attn_metadata.encoder_seq_lens,
+            attn_metadata.encoder_seq_lens_tensor,
+            attn_metadata.max_encoder_seq_len,
+            attn_metadata.cross_slot_mapping,
+            attn_metadata.cross_block_tables,
+        ) = (
+            sum(encoder_seq_lens),
+            encoder_seq_lens,
+            encoder_seq_lens_tensor,
+            max_encoder_seq_len,
+            cross_slot_mapping_tensor,
+            cross_block_tables,
+        )
+
+        return (attn_metadata, encoder_input_tokens_tensor,
+                encoder_input_positions_tensor)

vllm/worker/utils.py

+'''
+Worker-related helper functions.
+'''
+
+from vllm.utils import STR_NOT_IMPL_ENC_DEC_ERR_STRS
+from vllm.worker.model_runner import GPUModelRunnerBase
+
+
+def assert_enc_dec_mr_supported_scenario(
+        enc_dec_mr: GPUModelRunnerBase) -> None:
+    '''
+    Asserted that the provided encoder/decoder model runner instance reflects
+    a supported scenario.
+    '''
+
+    if enc_dec_mr.cache_config.enable_prefix_caching:
+        raise NotImplementedError(
+            STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_PREFIX_CACHE'])
+
+    if enc_dec_mr.sliding_window is not None:
+        raise NotImplementedError(
+            STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_SWA'])
+
+    if enc_dec_mr.scheduler_config.chunked_prefill_enabled:
+        raise NotImplementedError(STR_NOT_IMPL_ENC_DEC_ERR_STRS[
+            'STR_NOT_IMPL_ENC_DEC_CHUNKED_PREFILL'])
+
+    if getattr(enc_dec_mr.model_config.hf_config, 'attn_logit_softcapping',
+               None) is not None:
+        raise NotImplementedError(
+            STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_LOGIT_SOFTCAP']
+        )
+
+    if enc_dec_mr.lora_config is not None:
+        raise NotImplementedError(
+            STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_LORA'])
+
+    if enc_dec_mr.parallel_config.pipeline_parallel_size > 1:
+        raise NotImplementedError(
+            STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_PP'])
+
+    if enc_dec_mr.multimodal_config is not None:
+        raise NotImplementedError(
+            STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_MM'])
+
+    if enc_dec_mr.scheduler_config.num_lookahead_slots > 0:
+        raise NotImplementedError(
+            STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_SPEC_DEC'])
+
+    if not enc_dec_mr.model_config.enforce_eager:
+        raise NotImplementedError(
+            STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_CUDA_GRAPH'])
+
+    if enc_dec_mr.prompt_adapter_config is not None:
+        raise NotImplementedError(STR_NOT_IMPL_ENC_DEC_ERR_STRS[
+            'STR_NOT_IMPL_ENC_DEC_PROMPT_ADAPTER'])

vllm/worker/worker.py

@@ -19,8 +19,11 @@ from vllm.model_executor.model_loader.tensorizer import TensorizerConfig
 from vllm.platforms import current_platform
 from vllm.prompt_adapter.request import PromptAdapterRequest
 from vllm.sequence import ExecuteModelRequest
+from vllm.utils import (is_embedding_model_config,
+                        is_encoder_decoder_model_config)
 from vllm.worker.cache_engine import CacheEngine
 from vllm.worker.embedding_model_runner import EmbeddingModelRunner
+from vllm.worker.enc_dec_model_runner import EncoderDecoderModelRunner
 from vllm.worker.model_runner import GPUModelRunnerBase, ModelRunner
 from vllm.worker.worker_base import LocalOrDistributedWorkerBase, WorkerInput
 
@@ -85,8 +88,10 @@ class Worker(LocalOrDistributedWorkerBase):
         ModelRunnerClass: Type[GPUModelRunnerBase] = ModelRunner
         if model_runner_cls is not None:
             ModelRunnerClass = model_runner_cls
-        elif self.model_config.embedding_mode:
+        elif self._is_embedding_model():
             ModelRunnerClass = EmbeddingModelRunner
+        elif self._is_encoder_decoder_model():
+            ModelRunnerClass = EncoderDecoderModelRunner
         self.model_runner: GPUModelRunnerBase = ModelRunnerClass(
             model_config,
             parallel_config,
@@ -107,6 +112,12 @@ class Worker(LocalOrDistributedWorkerBase):
         # Initialize gpu_cache as embedding models don't initialize kv_caches
         self.gpu_cache: Optional[List[List[torch.Tensor]]] = None
 
+    def _is_encoder_decoder_model(self):
+        return is_encoder_decoder_model_config(self.model_config)
+
+    def _is_embedding_model(self):
+        return is_embedding_model_config(self.model_config)
+
     def init_device(self) -> None:
         if self.device_config.device.type == "cuda":
             # torch.distributed.all_reduce does not free the input tensor until