[Core] Add sleep level 0 mode with enqueue/wait pattern (#33195)

Signed-off-by: Jaewon Lee <jaewon@meta.com>
Co-authored-by: Lu Fang <30275821+houseroad@users.noreply.github.com>

vllm/entrypoints/llm.py

@@ -458,6 +458,93 @@ class LLM:
 
         return self.engine_class.validate_outputs(outputs, RequestOutput)
 
+    def enqueue(
+        self,
+        prompts: PromptType | Sequence[PromptType],
+        sampling_params: SamplingParams | Sequence[SamplingParams] | None = None,
+        lora_request: list[LoRARequest] | LoRARequest | None = None,
+        priority: list[int] | None = None,
+        use_tqdm: bool | Callable[..., tqdm] = True,
+        tokenization_kwargs: dict[str, Any] | None = None,
+    ) -> list[str]:
+        """Enqueue prompts for generation without waiting for completion.
+
+        This method adds requests to the engine queue but does not start
+        processing them. Use wait_for_completion() to process the queued
+        requests and get results.
+
+        Args:
+            prompts: The prompts to the LLM. See generate() for details.
+            sampling_params: The sampling parameters for text generation.
+            lora_request: LoRA request to use for generation, if any.
+            priority: The priority of the requests, if any.
+            use_tqdm: If True, shows a tqdm progress bar while adding requests.
+            tokenization_kwargs: Overrides for `tokenizer.encode`.
+
+        Returns:
+            A list of request IDs for the enqueued requests.
+        """
+        model_config = self.model_config
+        runner_type = model_config.runner_type
+        if runner_type != "generate":
+            raise ValueError("LLM.enqueue() is only supported for generative models.")
+
+        if sampling_params is None:
+            sampling_params = self.get_default_sampling_params()
+
+        # Use the same preprocessing as _run_completion
+        seq_prompts = prompt_to_seq(prompts)
+        seq_params = self._params_to_seq(sampling_params, len(seq_prompts))
+
+        if any(param.truncate_prompt_tokens is not None for param in seq_params):
+            engine_prompts: Sequence[DictPrompt | TokPrompt] = [
+                engine_prompt
+                for prompt, param in zip(seq_prompts, seq_params)
+                for engine_prompt in self._preprocess_completion(
+                    [prompt],
+                    tokenization_kwargs=merge_kwargs(
+                        tokenization_kwargs,
+                        dict(truncate_prompt_tokens=param.truncate_prompt_tokens),
+                    ),
+                )
+            ]
+        else:
+            engine_prompts = self._preprocess_completion(
+                seq_prompts,
+                tokenization_kwargs=tokenization_kwargs,
+            )
+
+        request_ids = self._validate_and_add_requests(
+            prompts=engine_prompts,
+            params=seq_params,
+            use_tqdm=use_tqdm,
+            lora_request=self._get_modality_specific_lora_reqs(
+                engine_prompts, lora_request
+            ),
+            tokenization_kwargs=tokenization_kwargs,
+            priority=priority,
+        )
+
+        return request_ids
+
+    def wait_for_completion(
+        self,
+        use_tqdm: bool | Callable[..., tqdm] = True,
+    ) -> list[RequestOutput]:
+        """Wait for all enqueued requests to complete and return results.
+
+        This method processes all requests currently in the engine queue
+        and returns their outputs. Use after enqueue() to get results.
+
+        Args:
+            use_tqdm: If True, shows a tqdm progress bar.
+
+        Returns:
+            A list of RequestOutput objects for all completed requests.
+        """
+        outputs = self._run_engine(use_tqdm=use_tqdm)
+        return self.engine_class.validate_outputs(outputs, RequestOutput)
+
     def _get_modality_specific_lora_reqs(
         self,
         prompts: Sequence[DictPrompt | TokPrompt],
@@ -1618,19 +1705,22 @@ class LLM:
         during the sleep period, before `wake_up` is called.
 
         Args:
-            level: The sleep level. Level 1 sleep will offload the model
-                weights and discard the kv cache. The content of kv cache
-                is forgotten. Level 1 sleep is good for sleeping and waking
-                up the engine to run the same model again. The model weights
-                are backed up in CPU memory. Please make sure there's enough
-                CPU memory to store the model weights. Level 2 sleep will
-                discard both the model weights and the kv cache. The content
-                of both the model weights and kv cache is forgotten. Level 2
-                sleep is good for sleeping and waking up the engine to run a
-                different model or update the model, where previous model
-                weights are not needed. It reduces CPU memory pressure.
+            level: The sleep level.
+                - Level 0: Pause scheduling but continue accepting requests.
+                           Requests are queued but not processed.
+                - Level 1: Offload model weights to CPU, discard KV cache.
+                           The content of kv cache is forgotten. Good for
+                           sleeping and waking up the engine to run the same
+                           model again. Please make sure there's enough CPU
+                           memory to store the model weights.
+                - Level 2: Discard all GPU memory (weights + KV cache).
+                           Good for sleeping and waking up the engine to run
+                           a different model or update the model, where
+                           previous model weights are not needed. It reduces
+                           CPU memory pressure.
         """
-        self.reset_prefix_cache()
+        if level > 0:
+            self.reset_prefix_cache()
         self.llm_engine.sleep(level=level)
 
     def wake_up(self, tags: list[str] | None = None):
@@ -1641,9 +1731,10 @@ class LLM:
         Args:
             tags: An optional list of tags to reallocate the engine memory
                 for specific memory allocations. Values must be in
-                `("weights", "kv_cache")`. If None, all memory is reallocated.
-                wake_up should be called with all tags (or None) before the
-                engine is used again.
+                `("weights", "kv_cache", "scheduling")`. If None, all memory
+                is reallocated. wake_up should be called with all tags
+                (or None) before the engine is used again.
+                Use tags=["scheduling"] to resume from level 0 sleep.
         """
         self.llm_engine.wake_up(tags)
 
@@ -1810,7 +1901,7 @@ class LLM:
         lora_request: Sequence[LoRARequest | None] | LoRARequest | None,
         tokenization_kwargs: dict[str, Any] | None = None,
         priority: list[int] | None = None,
-    ) -> None:
+    ) -> list[str]:
         num_requests = len(prompts)
         seq_params = self._params_to_seq(params, num_requests)
         seq_lora_requests = self._lora_request_to_seq(lora_request, num_requests)
@@ -1844,6 +1935,8 @@ class LLM:
                 self.llm_engine.abort_request(added_request_ids, internal=True)
             raise e
 
+        return added_request_ids
+
     def _add_request(
         self,
         prompt: PromptType | DictPrompt | TokPrompt,
@@ -1895,7 +1988,9 @@ class LLM:
         return engine_request.request_id
 
     def _run_engine(
-        self, *, use_tqdm: bool | Callable[..., tqdm] = True
+        self,
+        *,
+        use_tqdm: bool | Callable[..., tqdm] = True,
     ) -> list[RequestOutput | PoolingRequestOutput]:
         # Initialize tqdm.
         if use_tqdm:

vllm/v1/engine/async_llm.py

@@ -938,7 +938,8 @@ class AsyncLLM(EngineClient):
         await self.engine_core.reset_encoder_cache_async()
 
     async def sleep(self, level: int = 1) -> None:
-        await self.reset_prefix_cache()
+        if level > 0:
+            await self.reset_prefix_cache()
         await self.engine_core.sleep_async(level)
 
         if self.logger_manager is not None:

vllm/v1/engine/core.py

@@ -614,13 +614,43 @@ class EngineCore:
         self.model_executor.reset_encoder_cache()
 
     def sleep(self, level: int = 1):
-        self.model_executor.sleep(level)
+        """Put the engine to sleep at the specified level.
+
+        Args:
+            level: Sleep level.
+                - Level 0: Pause scheduling only. Requests are still accepted
+                           but not processed. No GPU memory changes.
+                - Level 1: Offload model weights to CPU, discard KV cache.
+                - Level 2: Discard all GPU memory.
+        """
+        if level == 0:
+            # Level 0: Just pause scheduling, don't touch GPU
+            self.pause_scheduler()
+        else:
+            # Level 1+: Delegate to executor for GPU memory management
+            self.model_executor.sleep(level)
 
     def wake_up(self, tags: list[str] | None = None):
-        self.model_executor.wake_up(tags)
+        """Wake up the engine from sleep.
+
+        Args:
+            tags: Tags to wake up. Use ["scheduling"] for level 0 wake up.
+        """
+        if tags is not None and "scheduling" in tags:
+            # Level 0 wake up: Resume scheduling
+            self.resume_scheduler()
+            # Remove "scheduling" from tags if there are other tags to process
+            remaining_tags = [t for t in tags if t != "scheduling"]
+            if remaining_tags:
+                self.model_executor.wake_up(remaining_tags)
+        else:
+            # Full wake up
+            self.resume_scheduler()
+            self.model_executor.wake_up(tags)
 
     def is_sleeping(self) -> bool:
-        return self.model_executor.is_sleeping
+        """Check if engine is sleeping at any level."""
+        return self._scheduler_paused or self.model_executor.is_sleeping
 
     def execute_dummy_batch(self):
         self.model_executor.execute_dummy_batch()
@@ -1023,7 +1053,13 @@ class EngineCoreProc(EngineCore):
             # 1) Poll the input queue until there is work to do.
             self._process_input_queue()
             # 2) Step the engine core and return the outputs.
-            self._process_engine_step()
+            #    Skip if scheduling is paused (level 0 sleep)
+            if not self._scheduler_paused:
+                self._process_engine_step()
+            else:
+                # When scheduling is paused, still need to check for wake up
+                # by processing any utility requests that might resume scheduling
+                pass
 
     def _process_input_queue(self):
         """Exits when an engine step needs to be performed."""
@@ -1031,7 +1067,7 @@ class EngineCoreProc(EngineCore):
         waited = False
         while (
             not self.engines_running
-            and not self.scheduler.has_requests()
+            and (not self.scheduler.has_requests() or self._scheduler_paused)
             and not self.batch_queue
             and not self._scheduler_paused
         ):
@@ -1414,11 +1450,15 @@ class DPEngineCoreProc(EngineCoreProc):
             # 1) Poll the input queue until there is work to do.
             self._process_input_queue()
 
+            # Skip processing if scheduling is paused (level 0 sleep)
+            if self._scheduler_paused:
+                continue
+
             # 2) Step the engine core.
             executed = self._process_engine_step()
             self._maybe_publish_request_counts()
-
             local_unfinished_reqs = self.scheduler.has_unfinished_requests()
+
             if not executed:
                 if not local_unfinished_reqs and not self.engines_running:
                     # All engines are idle.

vllm/v1/engine/core_client.py

@@ -194,7 +194,7 @@ class EngineCoreClient(ABC):
         raise NotImplementedError
 
     def dp_engines_running(self) -> bool:
-        """Returns True id data parallel engines are collectively in a
+        """Returns True if data parallel engines are collectively in a
         running state."""
         raise NotImplementedError
 
@@ -724,6 +724,7 @@ class SyncMPClient(MPClient):
         # it is forwarded to the outputs_queue so we can raise it
         # from this (run_output_handler) task to shut down the server.
         outputs = self.outputs_queue.get()
+
         if isinstance(outputs, Exception):
             raise self._format_exception(outputs) from None
         if outputs.wave_complete is not None:

vllm/v1/engine/llm_engine.py

@@ -312,7 +312,11 @@ class LLMEngine:
 
         # 4) Record stats
         with record_function_or_nullcontext("llm_engine step: record_stats"):
-            if self.logger_manager is not None and outputs.scheduler_stats is not None:
+            if (
+                self.logger_manager is not None
+                and outputs.scheduler_stats is not None
+                and len(outputs.outputs) > 0
+            ):
                 self.logger_manager.record(
                     scheduler_stats=outputs.scheduler_stats,
                     iteration_stats=iteration_stats,