[Diffusion] Fix DLO DP concurrent request execution (#5864)

Signed-off-by: lishunyang12 <lishunyang12@163.com>

tests/diffusion/test_diffusion_engine.py

@@ -331,6 +331,55 @@ class TestRequestBatchCapability:
             DiffusionEngine(od_config)
         fake_executor_cls.assert_not_called()
 
+    def test_engine_allows_independent_dlo_dp_requests_for_single_request_pipeline(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+        mocker: MockerFixture,
+    ) -> None:
+        od_config = SimpleNamespace(
+            model_class_name="SinglePipeline",
+            custom_pipeline_args=None,
+            streaming_output=False,
+            max_num_seqs=2,
+            request_batch_max_wait_ms=0,
+            parallel_config=SimpleNamespace(data_parallel_size=2),
+            enable_distributed_layerwise_offload=True,
+            dlo_use_allgather=True,
+        )
+        fake_executor = SimpleNamespace(
+            execute_request=mocker.Mock(return_value="per-request"),
+            execute_batch=mocker.Mock(return_value="batch"),
+            execute_step=mocker.Mock(return_value="step"),
+        )
+        fake_executor_cls = mocker.Mock(return_value=fake_executor)
+
+        monkeypatch.setattr(
+            "vllm_omni.diffusion.diffusion_engine.get_diffusion_post_process_func",
+            lambda *args, **kwargs: None,
+        )
+        monkeypatch.setattr(
+            "vllm_omni.diffusion.diffusion_engine.get_diffusion_pre_process_func",
+            lambda *args, **kwargs: None,
+        )
+        monkeypatch.setattr(
+            "vllm_omni.diffusion.diffusion_engine.DiffusionExecutor.get_class",
+            lambda *args, **kwargs: fake_executor_cls,
+        )
+        monkeypatch.setattr(
+            diffusion_engine_module.DiffusionModelRegistry,
+            "_try_load_model_cls",
+            lambda model_class_name: _SingleRequestPipeline,
+        )
+
+        engine = DiffusionEngine(od_config)
+
+        assert engine.execution_mode == DiffusionExecutionMode.REQUEST_BATCH
+        assert engine.supports_request_batch is False
+        assert engine.dp_concurrent is True
+        assert engine.scheduler.max_num_running_reqs == 2
+        assert od_config.request_batch_max_wait_ms == 0
+        fake_executor_cls.assert_called_once_with(od_config)
+
     @pytest.mark.parametrize("request_ids", [("req-a",), ("req-a", "req-b")])
     def test_engine_enables_batch_dispatch_for_request_batch_pipeline(
         self,