[Rebase] Rebase to vllm 0.27.0 (#5976)

Signed-off-by: tzhouam <tzhouam@connect.ust.hk>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/diffusion/distributed/test_expert_parallel_layout.py

@@ -64,6 +64,7 @@ def test_moe_ep_maps_diffusion_sp_cfg_dp_to_vllm_groups(monkeypatch):
         local_rank,
         backend,
         group_name,
+        use_all2all=False,
     ):
         del backend
         group = _FakeGroup(
@@ -73,6 +74,7 @@ def test_moe_ep_maps_diffusion_sp_cfg_dp_to_vllm_groups(monkeypatch):
             device_communicator=object(),
             reduce_scatter=lambda tensor, **kwargs: tensor,
         )
+        group.use_all2all = use_all2all
         created_groups.append(group)
         return group
 
@@ -121,6 +123,9 @@ def test_moe_ep_maps_diffusion_sp_cfg_dp_to_vllm_groups(monkeypatch):
     assert parallel_state.vllm_parallel_state._PCP.device_communicator is not None
     assert parallel_state.vllm_parallel_state._DP.device_communicator is not None
     assert parallel_state.vllm_parallel_state._EP.device_communicator is not None
+    # vLLM 0.27's MoE oracle asserts the EP communicator has an all2all
+    # manager, which vLLM only builds for groups created with use_all2all.
+    assert parallel_state.vllm_parallel_state._EP.use_all2all is True
     assert hasattr(parallel_state.vllm_parallel_state._PCP, "reduce_scatter")
     assert hasattr(parallel_state.vllm_parallel_state._DP, "reduce_scatter")
     assert hasattr(parallel_state.vllm_parallel_state._EP, "reduce_scatter")
@@ -313,3 +318,35 @@ def test_non_moe_ep_fails_before_vllm_ep_remap(monkeypatch):
     assert parallel_state.vllm_parallel_state._PCP is None
     assert parallel_state.vllm_parallel_state._EP is None
     assert parallel_state._EXPERT_PARALLEL_GROUP_RANKS is None
+
+
+@pytest.mark.cpu
+@pytest.mark.core_model
+def test_init_vllm_group_forwards_use_all2all_only_when_supported(monkeypatch):
+    """use_all2all reaches vLLM only on versions whose API accepts it.
+
+    vLLM 0.27 builds the EP all2all manager only for groups created with
+    use_all2all=True (its MoE oracle then asserts the manager exists —
+    build 2953, HunyuanImage3-DIT accuracy). Older vLLM has no such kwarg,
+    so forwarding it unconditionally would TypeError at init.
+    """
+    received = {}
+
+    def modern(group_ranks, local_rank, backend, group_name=None, use_device_communicator=True, use_all2all=False):
+        received["modern"] = use_all2all
+        return object()
+
+    monkeypatch.setattr(parallel_state.vllm_parallel_state, "init_model_parallel_group", modern)
+    parallel_state.init_vllm_model_parallel_group([[0]], 0, "gloo", "ep", use_all2all=True)
+    assert received["modern"] is True
+
+    parallel_state.init_vllm_model_parallel_group([[0]], 0, "gloo", "tp")
+    assert received["modern"] is False
+
+    def legacy(group_ranks, local_rank, backend, group_name=None, use_device_communicator=True):
+        received["legacy"] = True
+        return object()
+
+    monkeypatch.setattr(parallel_state.vllm_parallel_state, "init_model_parallel_group", legacy)
+    parallel_state.init_vllm_model_parallel_group([[0]], 0, "gloo", "ep", use_all2all=True)
+    assert received["legacy"] is True