[DOC] Add additional comments for LLMEngine and AsyncLLMEngine (#1011)

docs/source/conf.py

@@ -9,11 +9,15 @@
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
-#
-# import os
-# import sys
-# sys.path.insert(0, os.path.abspath('.'))
 
+import os
+import sys
+from sphinx.ext import autodoc
+import logging
+
+sys.path.insert(0, os.path.abspath(os.path.join('..', '..')))
+
+logger = logging.getLogger(__name__)
 
 # -- Project information -----------------------------------------------------
 
@@ -21,7 +25,6 @@ project = 'vLLM'
 copyright = '2023, vLLM Team'
 author = 'the vLLM Team'
 
-
 # -- General configuration ---------------------------------------------------
 
 # Add any Sphinx extension module names here, as strings. They can be
@@ -32,6 +35,8 @@ extensions = [
     "sphinx.ext.viewcode",
     "sphinx.ext.intersphinx",
     "sphinx_copybutton",
+    "sphinx.ext.autodoc",
+    "sphinx.ext.autosummary",
 ]
 
 # Add any paths that contain templates here, relative to this directory.
@@ -55,7 +60,6 @@ html_title = project
 html_theme = 'sphinx_book_theme'
 html_logo = 'assets/logos/vllm-logo-text-light.png'
 html_theme_options = {
-    'logo_only': True,
     'path_to_docs': 'docs/source',
     'repository_url': 'https://github.com/vllm-project/vllm',
     'use_repository_button': True,
@@ -64,4 +68,29 @@ html_theme_options = {
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+# html_static_path = ['_static']
+
+# Mock out external dependencies here.
+autodoc_mock_imports = [
+    "torch", "transformers", "psutil", "aioprometheus", "sentencepiece",
+    "vllm.cuda_utils", "vllm._C"
+]
+
+for mock_target in autodoc_mock_imports:
+    if mock_target in sys.modules:
+        logger.info(
+            f"Potentially problematic mock target ({mock_target}) found; "
+            "autodoc_mock_imports cannot mock modules that have already "
+            "been loaded into sys.modules when the sphinx build starts.")
+
+
+class MockedClassDocumenter(autodoc.ClassDocumenter):
+    """Remove note about base class when a class is derived from object."""
+
+    def add_line(self, line: str, source: str, *lineno: int) -> None:
+        if line == "   Bases: :py:class:`object`":
+            return
+        super().add_line(line, source, *lineno)
+
+
+autodoc.ClassDocumenter = MockedClassDocumenter

docs/source/dev/engine/async_llm_engine.rst

@@ -0,0 +1,7 @@
+
+AsyncLLMEngine
+=================================
+
+.. autoclass:: vllm.engine.async_llm_engine.AsyncLLMEngine
+    :members: generate, abort
+    :show-inheritance:

docs/source/dev/engine/engine_index.rst

@@ -0,0 +1,13 @@
+vLLM Engine
+=================================
+
+.. automodule:: vllm.engine
+.. currentmodule:: vllm.engine
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Engines
+
+   llm_engine
+   async_llm_engine
+

docs/source/dev/engine/llm_engine.rst

@@ -0,0 +1,6 @@
+LLMEngine
+=================================
+
+.. autoclass:: vllm.engine.llm_engine.LLMEngine
+    :members: add_request, abort_request, step, _init_cache
+    :show-inheritance:

docs/source/index.rst

@@ -85,4 +85,16 @@ Documentation
    :maxdepth: 1
    :caption: Quantization
 
-   quantization/auto_awq
+   quantization/auto_awq
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Developer Documentation
+
+   dev/engine/engine_index
+
+Indices and tables
+==================
+
+* :ref:`genindex`
+* :ref:`modindex`

vllm/core/scheduler.py

@@ -88,6 +88,18 @@ class Scheduler:
         self.waiting.append(seq_group)
 
     def abort_seq_group(self, request_id: Union[str, Iterable[str]]) -> None:
+        """Aborts a sequence group with the given ID.
+
+        Check if the sequence group with the given ID
+            is present in any of the state queue.
+        If present, remove the sequence group from the state queue.
+            Also, if any of the sequences in the sequence group is not finished,
+                free the sequence with status `FINISHED_ABORTED`.
+        Otherwise, do nothing.
+
+        Args:
+            request_id: The ID(s) of the sequence group to abort.
+        """
         if isinstance(request_id, str):
             request_id = (request_id, )
         request_ids = set(request_id)

vllm/engine/async_llm_engine.py

@@ -253,7 +253,8 @@ class AsyncLLMEngine:
         log_requests: Whether to log the requests.
         start_engine_loop: If True, the background task to run the engine
             will be automatically started in the generate call.
-        *args, *kwargs: Arguments for LLMEngine.
+        *args: Arguments for LLMEngine.
+        *kwargs: Arguments for LLMEngine.
     """
 
     _engine_class: Type[_AsyncLLMEngine] = _AsyncLLMEngine
@@ -428,6 +429,49 @@ class AsyncLLMEngine:
         Yields:
             The output `RequestOutput` objects from the LLMEngine for the
             request.
+
+        Details:
+            - If the engine is not running, start the background loop,
+              which iteratively invokes
+              :meth:`~vllm.engine.async_llm_engine.AsyncLLMEngine.engine_step`
+              to process the waiting requests.
+            - Add the request to the engine's `RequestTracker`.
+              On the next background loop, this request will be sent to
+              the underlying engine.
+              Also, a corresponding `AsyncStream` will be created.
+            - Wait for the request outputs from `AsyncStream` and yield them.
+
+        Example:
+            >>> # Please refer to entrypoints/api_server.py for
+            >>> # the complete example.
+            >>>
+            >>> # initialize the engine and the example input
+            >>> engine = AsyncLLMEngine.from_engine_args(engine_args)
+            >>> example_input = {
+            >>>     "prompt": "What is LLM?",
+            >>>     "stream": False, # assume the non-streaming case
+            >>>     "temperature": 0.0,
+            >>>     "request_id": 0,
+            >>> }
+            >>>
+            >>> # start the generation
+            >>> results_generator = engine.generate(
+            >>>    example_input["prompt"],
+            >>>    SamplingParams(temperature=example_input["temperature"]),
+            >>>    example_input["request_id"])
+            >>>
+            >>> # get the results
+            >>> final_output = None
+            >>> async for request_output in results_generator:
+            >>>     if await request.is_disconnected():
+            >>>         # Abort the request if the client disconnects.
+            >>>         await engine.abort(request_id)
+            >>>         # Return or raise an error
+            >>>         ...
+            >>>     final_output = request_output
+            >>>
+            >>> # Process and return the final output
+            >>> ...
         """
         # Preprocess the request.
         # This should not be used for logging, as it is monotonic time.

vllm/engine/llm_engine.py

@@ -257,7 +257,26 @@ class LLMEngine:
         self.cache_config.verify_with_parallel_config(self.parallel_config)
 
     def _init_cache(self) -> None:
-        """Profiles the memory usage and initializes the KV cache."""
+        """Profiles the memory usage and initializes the KV cache.
+
+        The engine will first conduct a profiling of the existing memory usage.
+        Then, it calculate the maximum possible number of GPU and CPU blocks
+        that can be allocated with the remaining free memory.
+        More details can be found in the
+        :meth:`~vllm.worker.worker.Worker.profile_num_available_blocks` method
+        from class :class:`~vllm.worker.Worker`.
+
+        Afterwards, as there may be multiple workers,
+        we take the minimum number of blocks across all workers
+        to ensure this can be applied to all of them.
+
+        Finally, the engine will initialize the KV cache
+        with the calculated number of blocks.
+
+        .. tip::
+            You may limit the usage of GPU memory
+            by adjusting the `gpu_memory_utilization` parameters.
+        """
         # Get the maximum number of blocks that can be allocated on GPU and CPU.
         num_blocks = self._run_workers(
             "profile_num_available_blocks",
@@ -334,6 +353,30 @@ class LLMEngine:
                 use the tokenizer to convert the prompts to token IDs.
             arrival_time: The arrival time of the request. If None, we use
                 the current monotonic time.
+
+        Details:
+            - Set arrival_time to the current time if it is None.
+            - Set prompt_token_ids to the encoded prompt if it is None.
+            - Create `best_of` number of :class:`~vllm.Sequence` objects.
+            - Create a :class:`~vllm.SequenceGroup` object
+              from the list of :class:`~vllm.Sequence`.
+            - Add the :class:`~vllm.SequenceGroup` object to the scheduler.
+
+        Example:
+            >>> # initialize engine
+            >>> engine = LLMEngine.from_engine_args(engine_args)
+            >>> # set request arguments
+            >>> example_prompt = "Who is the president of the United States?"
+            >>> sampling_params = SamplingParams(temperature=0.0)
+            >>> request_id = 0
+            >>>
+            >>> # add the request to the engine
+            >>> engine.add_request(
+            >>>    str(request_id),
+            >>>    example_prompt,
+            >>>    SamplingParams(temperature=0.0))
+            >>> # continue the request processing
+            >>> ...
         """
         if arrival_time is None:
             arrival_time = time.monotonic()
@@ -358,6 +401,17 @@ class LLMEngine:
 
         Args:
             request_id: The ID(s) of the request to abort.
+
+        Details:
+            - Refer to the
+              :meth:`~vllm.core.scheduler.Scheduler.abort_seq_group`
+              from class :class:`~vllm.core.scheduler.Scheduler`.
+
+        Example:
+            >>> # initialize engine and add a request with request_id
+            >>> request_id = str(0)
+            >>> # abort the request
+            >>> engine.abort_request(request_id)
         """
         self.scheduler.abort_seq_group(request_id)
 
@@ -617,11 +671,53 @@ class LLMEngine:
     def step(self) -> List[RequestOutput]:
         """Performs one decoding iteration and returns newly generated results.
 
-        This function performs one decoding iteration of the engine. It first
-        schedules the sequences to be executed in the next iteration and the
-        token blocks to be swapped in/out/copy. Then, it executes the model
-        and updates the scheduler with the model outputs. Finally, it decodes
-        the sequences and returns the newly generated results.
+        .. figure:: https://i.imgur.com/sv2HssD.png
+            :alt: Overview of the step function
+            :align: center
+
+            Overview of the step function.
+
+        Details:
+            - Step 1: Schedules the sequences to be executed in the next
+              iteration and the token blocks to be swapped in/out/copy.
+
+                - Depending on the scheduling policy,
+                  sequences may be `preempted/reordered`.
+                - A Sequence Group (SG) refer to a group of sequences
+                  that are generated from the same prompt.
+
+            - Step 2: Calls the workers to execute the model.
+            - Step 3: Processes the model output. This mainly includes:
+
+                - Decodes the relevant outputs.
+                - Updates the scheduled sequence groups with model outputs
+                  based on its `sampling parameters` (`use_beam_search` or not).
+                - Frees the finished sequence groups.
+
+            - Finally, it creates and returns the newly generated results.
+
+        Example:
+            >>> # Please see the example/ folder for more detailed examples.
+            >>>
+            >>> # initialize engine and request arguments
+            >>> engine = LLMEngine.from_engine_args(engine_args)
+            >>> example_inputs = [(0, "What is LLM?",
+            >>>    SamplingParams(temperature=0.0))]
+            >>>
+            >>> # Start the engine with an event loop
+            >>> while True:
+            >>>     if example_inputs:
+            >>>         req_id, prompt, sampling_params = example_inputs.pop(0)
+            >>>         engine.add_request(str(req_id), prompt, sampling_params)
+            >>>
+            >>>     # continue the request processing
+            >>>     request_outputs = engine.step()
+            >>>     for request_output in request_outputs:
+            >>>         if request_output.finished:
+            >>>             # return or show the request output
+            >>>
+            >>>     if not (engine.has_unfinished_requests() or example_inputs):
+            >>>         break
         """
         seq_group_metadata_list, scheduler_outputs = self.scheduler.schedule()
 

vllm/worker/worker.py

@@ -87,6 +87,14 @@ class Worker:
         gpu_memory_utilization: float,
         cpu_swap_space: int,
     ) -> Tuple[int, int]:
+        """Profiles the peak memory usage of the model and returns the maximum
+        number of GPU and CPU cache blocks that can be allocated.
+
+        Args:
+            block_size: The size of the cache block.
+            gpu_memory_utilization: The fraction of the total GPU memory to use.
+            cpu_swap_space: The size of the CPU swap space in bytes.
+        """
         # Profile the memory usage of the model and get the maximum number of
         # cache blocks that can be allocated with the remaining free memory.
         torch.cuda.empty_cache()