[platform] add base class for communicators (#13208)

Signed-off-by: youkaichao <youkaichao@gmail.com>

vllm/distributed/device_communicators/cpu_communicator.py

@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: Apache-2.0
+
+from typing import Optional
+
+import torch
+from torch.distributed import ProcessGroup
+
+from .base_device_communicator import DeviceCommunicatorBase
+
+
+class CpuCommunicator(DeviceCommunicatorBase):
+
+    def __init__(self,
+                 cpu_group: ProcessGroup,
+                 device: Optional[torch.device] = None,
+                 device_group: Optional[ProcessGroup] = None,
+                 unique_name: str = ""):
+        super().__init__(cpu_group, device, device_group, unique_name)
+        self.ipex_available = False
+        self.dist_module = torch.distributed
+        try:
+            import intel_extension_for_pytorch as ipex
+            self.ipex_available = True
+            self.dist_module = ipex.distributed
+        except ImportError:
+            """
+            Intel IPEX not found. Falling back to PyTorch native 
+            all_reduce for CPU (e.g. MacOS)
+            """
+            pass
+
+    def all_reduce(self, input_):
+        return self.dist_module.all_reduce(input_, group=self.device_group)