[Perf] Add skip_clone to SamplingParams for internal request handling (#31041)

Signed-off-by: mgoin <mgoin64@gmail.com>

vllm/entrypoints/api_server.py

@@ -60,7 +60,8 @@ async def generate(request: Request) -> Response:
 async def _generate(request_dict: dict, raw_request: Request) -> Response:
     prompt = request_dict.pop("prompt")
     stream = request_dict.pop("stream", False)
-    sampling_params = SamplingParams(**request_dict)
+    # Since SamplingParams is created fresh per request, safe to skip clone
+    sampling_params = SamplingParams(**request_dict, skip_clone=True)
     request_id = random_uuid()
 
     assert engine is not None

vllm/entrypoints/llm.py

@@ -642,7 +642,10 @@ class LLM:
         # following the huggingface transformers implementation
         # at https://github.com/huggingface/transformers/blob/e15687fffe5c9d20598a19aeab721ae0a7580f8a/src/transformers/generation/beam_search.py#L534 # noqa
         beam_search_params = SamplingParams(
-            logprobs=2 * beam_width, max_tokens=1, temperature=temperature
+            logprobs=2 * beam_width,
+            max_tokens=1,
+            temperature=temperature,
+            skip_clone=True,  # Internal beam search, safe to skip clone
         )
         instances: list[BeamSearchInstance] = []
 

vllm/entrypoints/openai/protocol.py

@@ -474,6 +474,7 @@ class ResponsesRequest(OpenAIBaseModel):
             ),
             structured_outputs=structured_outputs,
             logit_bias=self.logit_bias,
+            skip_clone=True,  # Created fresh per request, safe to skip clone
         )
 
     def is_include_output_logprobs(self) -> bool:
@@ -876,6 +877,7 @@ class ChatCompletionRequest(OpenAIBaseModel):
             bad_words=self.bad_words,
             allowed_token_ids=self.allowed_token_ids,
             extra_args=extra_args or None,
+            skip_clone=True,  # Created fresh per request, safe to skip clone
         )
 
     @model_validator(mode="before")
@@ -1316,6 +1318,7 @@ class CompletionRequest(OpenAIBaseModel):
             logit_bias=self.logit_bias,
             allowed_token_ids=self.allowed_token_ids,
             extra_args=extra_args or None,
+            skip_clone=True,  # Created fresh per request, safe to skip clone
         )
 
     @model_validator(mode="before")
@@ -2182,6 +2185,7 @@ class TranscriptionRequest(OpenAIBaseModel):
             if self.stream
             else RequestOutputKind.FINAL_ONLY,
             extra_args=self.vllm_xargs,
+            skip_clone=True,  # Created fresh per request, safe to skip clone
         )
 
     @model_validator(mode="before")
@@ -2409,6 +2413,7 @@ class TranslationRequest(OpenAIBaseModel):
             output_kind=RequestOutputKind.DELTA
             if self.stream
             else RequestOutputKind.FINAL_ONLY,
+            skip_clone=True,  # Created fresh per request, safe to skip clone
         )
 
     @model_validator(mode="before")

vllm/entrypoints/openai/speech_to_text.py

@@ -219,6 +219,7 @@ class OpenAISpeechToText(OpenAIServing):
             dummy_params = SamplingParams(
                 max_tokens=1,
                 temperature=0.0,
+                skip_clone=True,  # Internal warmup, safe to skip clone
             )
 
             # Process the dummy input through the input processor

vllm/sampling_params.py

@@ -211,6 +211,12 @@ class SamplingParams(
     set to an integer k, will use only the last k tokens from the prompt
     (i.e., left truncation). If set to `None`, truncation is disabled."""
     output_kind: RequestOutputKind = RequestOutputKind.CUMULATIVE
+    skip_clone: bool = False
+    """Internal flag indicating that this SamplingParams instance is safe to
+    reuse without cloning. When True, clone() will return self without
+    performing a deep copy. This should only be set when the params object
+    is guaranteed to be dedicated to a single request and won't be modified
+    in ways that would affect other uses."""
 
     # The below fields are not supposed to be used as an input.
     # They are set in post_init.
@@ -270,6 +276,7 @@ class SamplingParams(
         logit_bias: dict[int, float] | dict[str, float] | None = None,
         allowed_token_ids: list[int] | None = None,
         extra_args: dict[str, Any] | None = None,
+        skip_clone: bool = False,
     ) -> "SamplingParams":
         if logit_bias is not None:
             # Convert token_id to integer
@@ -310,6 +317,7 @@ class SamplingParams(
             logit_bias=logit_bias,
             allowed_token_ids=allowed_token_ids,
             extra_args=extra_args,
+            skip_clone=skip_clone,
         )
 
     def __post_init__(self) -> None:
@@ -540,8 +548,13 @@ class SamplingParams(
         data that is expensive to copy. However, if not copied, the processor
         needs to support parallel decoding for multiple sequences
         See https://github.com/vllm-project/vllm/issues/3087
+
+        If skip_clone is True, uses shallow copy instead of deep copy.
         """
 
+        if self.skip_clone:
+            return copy.copy(self)
+
         logit_processor_refs = (
             None
             if self.logits_processors is None