[core][V1] pluggable scheduler (#14466)

Signed-off-by: Joe Runde <Joseph.Runde@ibm.com>

tests/plugins_tests/test_scheduler_plugins.py

 # SPDX-License-Identifier: Apache-2.0
 
+import pytest
+
 from vllm.core.scheduler import Scheduler
+from vllm.engine.arg_utils import EngineArgs
+from vllm.engine.llm_engine import LLMEngine
+from vllm.sampling_params import SamplingParams
+from vllm.v1.core.scheduler import Scheduler as V1Scheduler
+from vllm.v1.engine.llm_engine import LLMEngine as V1LLMEngine
 
 
-class DummyScheduler(Scheduler):
+class DummyV0Scheduler(Scheduler):
 
     def schedule(self):
-        raise Exception("Exception raised by DummyScheduler")
+        raise Exception("Exception raised by DummyV0Scheduler")
+
 
+class DummyV1Scheduler(V1Scheduler):
 
-def test_scheduler_plugins():
-    import pytest
+    def schedule(self):
+        raise Exception("Exception raised by DummyV1Scheduler")
 
-    from vllm.engine.arg_utils import EngineArgs
-    from vllm.engine.llm_engine import LLMEngine
-    from vllm.sampling_params import SamplingParams
 
+def test_scheduler_plugins_v0(monkeypatch):
+    monkeypatch.setenv("VLLM_USE_V1", "0")
     with pytest.raises(Exception) as exception_info:
 
         engine_args = EngineArgs(
             model="facebook/opt-125m",
             enforce_eager=True,  # reduce test time
-            scheduler_cls=DummyScheduler,
+            scheduler_cls=DummyV0Scheduler,
         )
 
         engine = LLMEngine.from_engine_args(engine_args=engine_args)
@@ -30,4 +38,27 @@ def test_scheduler_plugins():
         engine.add_request("0", "foo", sampling_params)
         engine.step()
 
-    assert str(exception_info.value) == "Exception raised by DummyScheduler"
+    assert str(exception_info.value) == "Exception raised by DummyV0Scheduler"
+
+
+def test_scheduler_plugins_v1(monkeypatch):
+    monkeypatch.setenv("VLLM_USE_V1", "1")
+    # Explicitly turn off engine multiprocessing so that the scheduler runs in
+    # this process
+    monkeypatch.setenv("VLLM_ENABLE_V1_MULTIPROCESSING", "0")
+
+    with pytest.raises(Exception) as exception_info:
+
+        engine_args = EngineArgs(
+            model="facebook/opt-125m",
+            enforce_eager=True,  # reduce test time
+            scheduler_cls=DummyV1Scheduler,
+        )
+
+        engine = V1LLMEngine.from_engine_args(engine_args=engine_args)
+
+        sampling_params = SamplingParams(max_tokens=1)
+        engine.add_request("0", "foo", sampling_params)
+        engine.step()
+
+    assert str(exception_info.value) == "Exception raised by DummyV1Scheduler"

vllm/engine/arg_utils.py

@@ -1437,6 +1437,11 @@ class EngineArgs:
 
         # V1 always uses chunked prefills.
         self.enable_chunked_prefill = True
+        # V1 should use the new scheduler by default.
+        # Swap it only if this arg is set to the original V0 default
+        if self.scheduler_cls == EngineArgs.scheduler_cls:
+            self.scheduler_cls = "vllm.v1.core.scheduler.Scheduler"
+
         # When no user override, set the default values based on the usage
         # context.
         # Use different default values for different hardware.

vllm/v1/engine/core.py

@@ -19,9 +19,10 @@ from vllm.logger import init_logger
 from vllm.lora.request import LoRARequest
 from vllm.transformers_utils.config import (
     maybe_register_config_serialize_by_value)
-from vllm.utils import get_exception_traceback, zmq_socket_ctx
+from vllm.utils import (get_exception_traceback, resolve_obj_by_qualname,
+                        zmq_socket_ctx)
 from vllm.v1.core.kv_cache_utils import get_kv_cache_configs
-from vllm.v1.core.scheduler import Scheduler, SchedulerOutput
+from vllm.v1.core.scheduler import SchedulerOutput
 from vllm.v1.engine import (EngineCoreOutputs, EngineCoreRequest,
                             EngineCoreRequestType, UtilityOutput)
 from vllm.v1.engine.mm_input_cache import MMInputCacheServer
@@ -65,6 +66,16 @@ class EngineCore:
         self.structured_output_manager = StructuredOutputManager(vllm_config)
 
         # Setup scheduler.
+        if isinstance(vllm_config.scheduler_config.scheduler_cls, str):
+            logger.warning(
+                "Using configured V1 scheduler class %s. "
+                "This scheduler interface is not public and "
+                "compatibility may not be maintained.",
+                vllm_config.scheduler_config.scheduler_cls)
+            Scheduler = resolve_obj_by_qualname(
+                vllm_config.scheduler_config.scheduler_cls)
+        else:
+            Scheduler = vllm_config.scheduler_config.scheduler_cls
         self.scheduler = Scheduler(
             scheduler_config=vllm_config.scheduler_config,
             model_config=vllm_config.model_config,