[Core] Add Lora Support to Beam Search (#18346)

Signed-off-by: Alex-Brooks <Alex.Brooks@ibm.com>

tests/entrypoints/openai/test_lora_adapters.py

@@ -313,3 +313,37 @@ async def test_loading_invalid_adapters_does_not_break_others(
         prompt=["Hello there", "Foo bar bazz buzz"],
         max_tokens=5,
     )
+
+
+@pytest.mark.asyncio
+async def test_beam_search_with_lora_adapters(
+    client: openai.AsyncOpenAI,
+    tmp_path,
+    zephyr_lora_files,
+):
+    """Validate that async beam search can be used with lora."""
+
+    async def load_and_run_adapter(adapter_name: str):
+        await client.post("load_lora_adapter",
+                          cast_to=str,
+                          body={
+                              "lora_name": adapter_name,
+                              "lora_path": str(zephyr_lora_files)
+                          })
+        for _ in range(3):
+            await client.completions.create(
+                model=adapter_name,
+                prompt=["Hello there", "Foo bar bazz buzz"],
+                max_tokens=5,
+                extra_body=dict(use_beam_search=True),
+            )
+
+    lora_tasks = []
+    for i in range(3):
+        lora_tasks.append(
+            asyncio.create_task(load_and_run_adapter(f"adapter_{i}")))
+
+    results, _ = await asyncio.wait(lora_tasks)
+
+    for r in results:
+        assert not isinstance(r, Exception), f"Got exception {r}"

tests/lora/test_qwen2vl.py

@@ -10,6 +10,7 @@ import vllm
 from vllm.assets.image import ImageAsset
 from vllm.lora.request import LoRARequest
 from vllm.platforms import current_platform
+from vllm.sampling_params import BeamSearchParams
 
 
 @pytest.fixture(autouse=not current_platform.is_cpu())
@@ -69,7 +70,7 @@ class Qwen2VLTester:
                  expected_outputs: list[str],
                  lora_id: Optional[int] = None,
                  temperature: float = 0,
-                 max_tokens: int = 5) -> list[str]:
+                 max_tokens: int = 5):
 
         sampling_params = vllm.SamplingParams(
             temperature=temperature,
@@ -97,7 +98,35 @@ class Qwen2VLTester:
                 generated), f"Generated text {generated} doesn't "
             f"match expected pattern {expected}"
 
-        return generated_texts
+    def run_beam_search_test(self,
+                             images: list[ImageAsset],
+                             expected_outputs: list[list[str]],
+                             lora_id: Optional[int] = None,
+                             temperature: float = 0,
+                             beam_width: int = 2,
+                             max_tokens: int = 5):
+
+        beam_search_params = BeamSearchParams(beam_width=beam_width,
+                                              max_tokens=max_tokens,
+                                              temperature=temperature)
+
+        inputs = [{
+            "prompt": self.PROMPT_TEMPLATE,
+            "multi_modal_data": {
+                "image": asset.pil_image
+            },
+        } for asset in images]
+
+        lora_request = LoRARequest(str(lora_id), lora_id,
+                                   self.config.lora_path)
+        outputs = self.llm.beam_search(inputs,
+                                       beam_search_params,
+                                       lora_request=lora_request)
+
+        for output_obj, expected_outs in zip(outputs, expected_outputs):
+            output_texts = [seq.text for seq in output_obj.sequences]
+            assert output_texts == expected_outs, \
+                f"Generated texts {output_texts} do not match expected {expected_outs}"  # noqa: E501
 
 
 TEST_IMAGES = [
@@ -110,6 +139,14 @@ EXPECTED_OUTPUTS = [
     "A majestic skyscraper stands tall, partially obscured by a vibrant canopy of cherry blossoms, against a clear blue sky.",  # noqa: E501
 ]
 
+# NOTE - beam search .text contains the whole text
+EXPECTED_BEAM_SEARCH_OUTPUTS = [
+    [
+        "<|im_start|>system\nYou are a helpful assistant.<|im_end|>\n<|im_start|>user\n<|vision_start|><|image_pad|><|vision_end|>What is in the image?<|im_end|>\n<|im_start|>assistant\nA majestic skyscraper stands",  # noqa: E501
+        "<|im_start|>system\nYou are a helpful assistant.<|im_end|>\n<|im_start|>user\n<|vision_start|><|image_pad|><|vision_end|>What is in the image?<|im_end|>\n<|im_start|>assistant\nA majestic tower stands tall",  # noqa: E501
+    ],
+]
+
 QWEN2VL_MODEL_PATH = "Qwen/Qwen2-VL-2B-Instruct"
 QWEN25VL_MODEL_PATH = "Qwen/Qwen2.5-VL-3B-Instruct"
 
@@ -130,6 +167,27 @@ def test_qwen2vl_lora(qwen2vl_lora_files):
                         lora_id=lora_id)
 
 
+@pytest.mark.xfail(
+    current_platform.is_rocm(),
+    reason="Qwen2-VL dependency xformers incompatible with ROCm")
+def test_qwen2vl_lora_beam_search(qwen2vl_lora_files):
+    """Test Qwen 2.0 VL model with LoRA through beam search."""
+    config = TestConfig(model_path=QWEN2VL_MODEL_PATH,
+                        lora_path=qwen2vl_lora_files)
+    tester = Qwen2VLTester(config)
+
+    # Test with different LoRA IDs
+    for lora_id in [1, 2]:
+        # NOTE currently, we only test cherry blossom since stop sign
+        # output is slightly different for v1; - the root cause is likely
+        # independent of the intent of this test, which is to ensure beam
+        # search passes through lora through correctly.
+        tester.run_beam_search_test(
+            [ImageAsset("cherry_blossom")],
+            expected_outputs=EXPECTED_BEAM_SEARCH_OUTPUTS,
+            lora_id=lora_id)
+
+
 @pytest.mark.xfail(
     current_platform.is_rocm(),
     reason="Qwen2.5-VL dependency xformers incompatible with ROCm",

vllm/beam_search.py

@@ -3,6 +3,7 @@
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Any, Optional, Union
 
+from vllm.lora.request import LoRARequest
 from vllm.sequence import Logprob
 
 if TYPE_CHECKING:
@@ -19,6 +20,7 @@ class BeamSearchSequence:
     # The tokens includes the prompt.
     tokens: list[int]
     logprobs: list[dict[int, Logprob]]
+    lora_request: Optional[LoRARequest] = None
     cum_logprob: float = 0.0
     text: Optional[str] = None
     finish_reason: Optional[str] = None
@@ -41,6 +43,7 @@ class BeamSearchInstance:
     def __init__(
         self,
         prompt_tokens: list[int],
+        lora_request: Optional[LoRARequest] = None,
         logprobs: Optional[list[dict[int, Logprob]]] = None,
         **kwargs,
     ):
@@ -48,6 +51,7 @@ class BeamSearchInstance:
             BeamSearchSequence(
                 tokens=prompt_tokens,
                 logprobs=[] if logprobs is None else list(logprobs),
+                lora_request=lora_request,
                 **kwargs,
             )
         ]

vllm/engine/protocol.py

@@ -65,6 +65,7 @@ class EngineClient(ABC):
         prompt: PromptType,
         request_id: str,
         params: BeamSearchParams,
+        lora_request: Optional[LoRARequest] = None,
     ) -> AsyncGenerator[RequestOutput, None]:
 
         beam_width = params.beam_width
@@ -106,27 +107,31 @@ class EngineClient(ABC):
                                cum_logprob=0,
                                logprobs=[],
                                multi_modal_data=multi_modal_data,
-                               mm_processor_kwargs=mm_processor_kwargs)
+                               mm_processor_kwargs=mm_processor_kwargs,
+                               lora_request=lora_request)
         ]
         completed = []
 
         for _ in range(max_tokens):
-            prompts_batch = [
+            prompts_batch, lora_req_batch = zip(*[(
                 TokensPrompt(prompt_token_ids=beam.tokens,
                              multi_modal_data=beam.multi_modal_data,
-                             mm_processor_kwargs=beam.mm_processor_kwargs)
-                for beam in all_beams
-            ]
+                             mm_processor_kwargs=beam.mm_processor_kwargs),
+                beam.lora_request,
+            ) for beam in all_beams])
 
             tasks = []
 
             request_id = f"beam_search-{random_uuid()}"
-            for i, individual_prompt in enumerate(prompts_batch):
+            for i, (individual_prompt,
+                    lora_req) in enumerate(zip(prompts_batch, lora_req_batch)):
                 request_id_item = f"{request_id}-{i}"
                 task = asyncio.create_task(
                     collect_from_async_generator(
-                        self.generate(individual_prompt, beam_search_params,
-                                      request_id_item)))
+                        self.generate(individual_prompt,
+                                      beam_search_params,
+                                      request_id_item,
+                                      lora_request=lora_req)))
                 tasks.append(task)
 
             output = await asyncio.gather(*tasks)
@@ -159,6 +164,7 @@ class EngineClient(ABC):
                                     tokens=current_beam.tokens + [token_id],
                                     logprobs=current_beam.logprobs +
                                     [logprobs],
+                                    lora_request=current_beam.lora_request,
                                     cum_logprob=current_beam.cum_logprob +
                                     logprob_obj.logprob,
                                     multi_modal_data=current_beam.

vllm/entrypoints/llm.py

@@ -522,10 +522,28 @@ class LLM:
         executor = self.llm_engine.model_executor
         return executor.apply_model(func)
 
+    def _get_beam_search_lora_requests(
+        self,
+        lora_request: Optional[Union[list[LoRARequest], LoRARequest]],
+        prompts: list[Union[TokensPrompt, TextPrompt]],
+    ) -> list[Optional[LoRARequest]]:
+        """Get the optional lora request corresponding to each prompt."""
+        if isinstance(lora_request,
+                      Sequence) and len(lora_request) != len(prompts):
+            raise ValueError(
+                "Lora request list should be the same length as the prompts")
+            return lora_request
+
+        if lora_request is None or isinstance(lora_request, LoRARequest):
+            return [lora_request] * len(prompts)
+
+        raise TypeError(f"Invalid lora_request type {type(lora_request)}")
+
     def beam_search(
         self,
         prompts: list[Union[TokensPrompt, TextPrompt]],
         params: BeamSearchParams,
+        lora_request: Optional[Union[list[LoRARequest], LoRARequest]] = None,
     ) -> list[BeamSearchOutput]:
         """
         Generate sequences using beam search.
@@ -534,6 +552,7 @@ class LLM:
             prompts: A list of prompts. Each prompt can be a string or a list
                 of token IDs.
             params: The beam search parameters.
+            lora_request: LoRA request to use for generation, if any.
         """
         # TODO: how does beam search work together with length penalty,
         # frequency, penalty, and stopping criteria, etc.?
@@ -543,6 +562,9 @@ class LLM:
         ignore_eos = params.ignore_eos
         length_penalty = params.length_penalty
 
+        lora_requests = self._get_beam_search_lora_requests(
+            lora_request, prompts)
+
         def sort_beams_key(x: BeamSearchSequence) -> float:
             return get_beam_search_score(x.tokens, x.cum_logprob,
                                          tokenizer.eos_token_id,
@@ -570,7 +592,7 @@ class LLM:
                                             temperature=temperature)
         instances: list[BeamSearchInstance] = []
 
-        for prompt in prompts:
+        for lora_req, prompt in zip(lora_requests, prompts):
             # Add multimodal processor kwargs & data
             mm_kwargs = {}
             if "multi_modal_data" in prompt:
@@ -586,7 +608,12 @@ class LLM:
                 prompt_tokens = tokenizer.encode(prompt["prompt"])
 
             instances.append(
-                BeamSearchInstance(prompt_tokens, logprobs=None, **mm_kwargs))
+                BeamSearchInstance(
+                    prompt_tokens,
+                    lora_request=lora_req,
+                    logprobs=None,
+                    **mm_kwargs,
+                ), )
 
         for _ in range(max_tokens):
             all_beams: list[BeamSearchSequence] = list(
@@ -600,15 +627,17 @@ class LLM:
             if len(all_beams) == 0:
                 break
 
-            prompts_batch = [
-                create_tokens_prompt_from_beam(beam) for beam in all_beams
-            ]
+            # create the corresponding batch entries for prompt & optional lora
+            prompts_batch, lora_req_batch = zip(
+                *[(create_tokens_prompt_from_beam(beam), beam.lora_request)
+                  for beam in all_beams])
 
             # only runs for one step
             # we don't need to use tqdm here
             output = self.generate(prompts_batch,
                                    sampling_params=beam_search_params,
-                                   use_tqdm=False)
+                                   use_tqdm=False,
+                                   lora_request=lora_req_batch)
 
             for (start, end), instance in zip(instance_start_and_end,
                                               instances):
@@ -626,6 +655,7 @@ class LLM:
                             new_beam = BeamSearchSequence(
                                 tokens=current_beam.tokens + [token_id],
                                 logprobs=current_beam.logprobs + [logprobs],
+                                lora_request=current_beam.lora_request,
                                 cum_logprob=current_beam.cum_logprob +
                                 logprob_obj.logprob,
                                 multi_modal_data=current_beam.multi_modal_data,

vllm/entrypoints/openai/serving_chat.py

@@ -236,6 +236,7 @@ class OpenAIServingChat(OpenAIServing):
                         prompt=engine_prompt,
                         request_id=request_id,
                         params=sampling_params,
+                        lora_request=lora_request,
                     )
                 else:
                     generator = self.engine_client.generate(

vllm/entrypoints/openai/serving_completion.py

@@ -186,6 +186,7 @@ class OpenAIServingCompletion(OpenAIServing):
                         prompt=engine_prompt,
                         request_id=request_id,
                         params=sampling_params,
+                        lora_request=lora_request,
                     )
                 else:
                     generator = self.engine_client.generate(