[core] Multi Step Scheduling (vllm-project#7000)

Co-authored-by: afeldman-nm <156691304+afeldman-nm@users.noreply.github.com>

.buildkite/test-pipeline.yaml

@@ -311,6 +311,15 @@ steps:
   - CUDA_VISIBLE_DEVICES=0,1 pytest -v -s test_sharded_state_loader.py
   - CUDA_VISIBLE_DEVICES=0,1 pytest -v -s distributed/test_utils.py
 
+- label: Multi-step Tests (4 GPUs) # 10min
+  working_dir: "/vllm-workspace/tests"
+  num_gpus: 4
+  source_file_dependencies:
+  - vllm/
+  - tests/multi_step/test_correctness.py
+  commands:
+  - pytest -v -s multi_step/test_correctness.py
+
 - label: Pipeline Parallelism Test # 23min
   working_dir: "/vllm-workspace/tests"
   num_gpus: 4

tests/multi_step/test_correctness.py

@@ -0,0 +1,85 @@
+# Test the AsyncLLMEngine with multi-step-decoding
+
+from typing import List
+
+import pytest
+
+from ..utils import RemoteOpenAIServer
+
+MODELS = [
+    "JackFram/llama-160m",
+]
+NUM_SCHEDULER_STEPS = [8]  # Multi-step decoding steps
+NUM_PROMPTS = [10]
+
+DEFAULT_SERVER_ARGS: List[str] = [
+    "--disable-log-requests",
+    "--use-v2-block-manager",
+    "--worker-use-ray",
+    "--gpu-memory-utilization",
+    "0.85",
+    "--swap-space",
+    "16",
+]
+
+
+async def completions_with_server_args(prompts: List[str], model_name: str,
+                                       server_cli_args: List[str]):
+
+    outputs = None
+    with RemoteOpenAIServer(model_name, server_cli_args) as server:
+        client = server.get_async_client()
+        outputs = await client.completions.create(model=model_name,
+                                                  prompt=prompts,
+                                                  temperature=0,
+                                                  stream=False,
+                                                  max_tokens=5)
+    assert outputs is not None
+
+    return outputs
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize(("tp_size, pp_size"), [
+    (1, 1),
+    (2, 2),
+])
+@pytest.mark.parametrize("eager_mode", [False, True])
+@pytest.mark.parametrize("num_scheduler_steps", NUM_SCHEDULER_STEPS)
+@pytest.mark.parametrize("num_prompts", NUM_PROMPTS)
+@pytest.mark.asyncio
+async def test_multi_step(example_prompts, model: str, tp_size: int,
+                          pp_size: int, eager_mode: int,
+                          num_scheduler_steps: int, num_prompts: int):
+
+    prompts = example_prompts
+    if len(prompts) < num_prompts:
+        prompts = prompts * ((num_prompts // len(prompts)) + 1)
+    prompts = prompts[:num_prompts]
+    assert len(prompts) == num_prompts
+
+    server_args = DEFAULT_SERVER_ARGS + ["--enforce-eager"]
+    ms_server_args = DEFAULT_SERVER_ARGS + \
+        ["--num-scheduler-steps", f"{num_scheduler_steps}"]
+
+    if eager_mode:
+        ms_server_args.append("--enforce-eager")
+
+    distributed_args = [
+        "--tensor-parallel-size",
+        str(tp_size),
+        "--pipeline-parallel-size",
+        str(pp_size),
+    ]
+
+    ref_completions = await completions_with_server_args(
+        prompts, model, server_args + distributed_args)
+    test_completions = await completions_with_server_args(
+        prompts, model, ms_server_args + distributed_args)
+
+    def get_text_generations(completions):
+        return [x.text for x in completions.choices]
+
+    ref_generations = get_text_generations(ref_completions)
+    test_generations = get_text_generations(test_completions)
+    assert ref_generations == test_generations

tests/worker/test_model_input.py

@@ -10,6 +10,7 @@
 from vllm.worker.embedding_model_runner import (
     ModelInputForGPUWithPoolingMetadata)
 from vllm.worker.model_runner import ModelInputForGPUWithSamplingMetadata
+from vllm.worker.multi_step_model_runner import StatefulModelInput
 
 
 class MockAttentionBackend(AttentionBackend):
@@ -154,3 +155,79 @@ def test_embedding_model_runner_input():
                        None) == getattr(attn_metadata, field.name, None)
     # Pooling metadata is not broadcast.
     assert received_model_input.pooling_metadata is None
+
+
+def test_multi_step_model_runner_input():
+    sampling_metadata = SamplingMetadata(
+        ["seq_group"],
+        "selected_token_indices",
+        "categorized_sample_indices",
+        "num_prompts",
+    )
+    attn_metadata = AttentionMetadata(
+        num_prefills=1,
+        num_prefill_tokens=2,
+        num_decode_tokens=3,
+        slot_mapping=torch.zeros(1),
+    )
+    frozen_model_input = ModelInputForGPUWithSamplingMetadata(
+        input_tokens=torch.ones(10),
+        input_positions=torch.ones(10),
+        sampling_metadata=sampling_metadata,
+        attn_metadata=attn_metadata)
+
+    model_input = StatefulModelInput(
+        frozen_model_input=frozen_model_input,
+        is_last_step=True,
+        is_first_multi_step=False,
+        current_step=4,
+        last_sampled_token_ids=torch.ones((10, 1)),
+        is_multi_step=True,
+        num_queries=8,
+        num_seqs=5,
+        cached_outputs=[],
+    )
+
+    assert isinstance(model_input, StatefulModelInput)
+
+    # Test round trip serialization.
+    tensor_dict = model_input.as_broadcastable_tensor_dict()
+    attn_backend = MockAttentionBackend()
+    received_model_input = (StatefulModelInput.from_broadcasted_tensor_dict(
+        tensor_dict, attn_backend=attn_backend))
+
+    receieved_frozen_input = received_model_input.frozen_model_input
+
+    # Check that received copy has correct values.
+    assert isinstance(received_model_input, StatefulModelInput)
+    assert receieved_frozen_input.input_tokens is not None
+    assert (receieved_frozen_input.input_tokens ==
+            frozen_model_input.input_tokens).all()
+    assert receieved_frozen_input.input_positions is not None
+    assert (receieved_frozen_input.input_positions ==
+            frozen_model_input.input_positions).all()
+    assert receieved_frozen_input.multi_modal_kwargs is None
+    assert (frozen_model_input.multi_modal_kwargs ==
+            frozen_model_input.multi_modal_kwargs)
+    assert receieved_frozen_input.lora_requests is None
+    assert (receieved_frozen_input.lora_requests ==
+            frozen_model_input.lora_requests)
+    assert receieved_frozen_input.lora_mapping is None
+    assert (
+        receieved_frozen_input.lora_mapping == frozen_model_input.lora_mapping)
+    for field in dataclasses.fields(AttentionMetadata):
+        assert getattr(receieved_frozen_input.attn_metadata, field.name,
+                       None) == getattr(attn_metadata, field.name, None)
+    # For sampling metadata, only selected_token_indices is copied.
+    assert (receieved_frozen_input.sampling_metadata.selected_token_indices ==
+            sampling_metadata.selected_token_indices)
+    assert receieved_frozen_input.sampling_metadata.seq_groups is None
+
+    # check non frozen fields
+    assert received_model_input.is_last_step == model_input.is_last_step
+    assert (received_model_input.is_first_multi_step ==
+            model_input.is_first_multi_step)
+    assert received_model_input.current_step == model_input.current_step
+    assert (received_model_input.last_sampled_token_ids ==
+            model_input.last_sampled_token_ids).all()
+    assert received_model_input.is_multi_step == model_input.is_multi_step

vllm/engine/arg_utils.py

@@ -853,6 +853,12 @@ def create_engine_config(self, ) -> EngineConfig:
                 "in low performance due to small KV cache space. Consider "
                 "setting --max-model-len to a smaller value.", max_model_len)
 
+        if self.num_scheduler_steps > 1 and not self.use_v2_block_manager:
+            self.use_v2_block_manager = True
+            logger.warning(
+                "Enabled BlockSpaceManagerV2 because it is "
+                "required for multi-step (--num-scheduler-steps > 1)")
+
         speculative_config = SpeculativeConfig.maybe_create_spec_config(
             target_model_config=model_config,
             target_parallel_config=parallel_config,
@@ -881,7 +887,6 @@ def create_engine_config(self, ) -> EngineConfig:
         )
 
         if self.num_scheduler_steps > 1:
-            raise NotImplementedError("Multi-step is not yet supported.")
             if speculative_config is not None:
                 raise ValueError("Speculative decoding is not supported with "
                                  "multi-step (--num-scheduler-steps > 1)")