[HiCache] add GPU id to IB dev topo for mooncake storage backend (#13112)

python/sglang/srt/mem_cache/storage/mooncake_store/README.md

@@ -104,6 +104,16 @@ Parameter Explanation:
 * `master_server_address`: The network address of the `master service`. The default port is 50051.
 * `protocol`: The protocol used by Mooncake. Supported values are `"rdma"` or `"tcp"`. For optimal performance, `"rdma"` is recommended.
 * `device_name`: For `"rdma"`, you can leave this empty in most cases. Mooncake auto-discovers RDMA NICs by default. If you want to pin specific NICs (e.g., `mlx5_0,mlx5_1`), just set `device_name` accordingly. To list available devices, use `ibv_devices`.
+  - For tensor parallel deployments where different ranks should use different devices, you can specify device configurations using JSON format:
+    ```json
+    {
+    "device_name": "{0: \"ib0,ib1\", 1: \"ib2,ib3\", 2: \"ib4,ib5\"}"
+    }
+    ```
+  - Or in environment variables:
+    ```bash
+    MOONCAKE_DEVICE="{\"0\": \"ib0,ib1\", \"1\": \"ib2,ib3\", \"2\": \"ib4,ib5\"}"
+    ```
 * `global_segment_size`: The amount of memory contributed to the global memory pool. Accepts either bytes (integer) or a string with the `gb` suffix, e.g., `"16gb"`. A larger value allows Mooncake to cache more KV tensors.
 * `local_buffer_size`: Local buffer is used to do request operations such as `Get` or `Put`. In this case, it is set to 0 because the instance functions solely as a storage server, contributing memory to the global pool without issuing any request operations.
 

python/sglang/srt/mem_cache/storage/mooncake_store/mooncake_store.py

@@ -190,13 +190,32 @@ class MooncakeStore(HiCacheStorage):
             if self.config.check_server:
                 self.check_server()
 
+            # Handle JSON device_name configuration
+            device_name = self.config.device_name
+            if device_name and device_name.strip().startswith("{"):
+                try:
+                    device_config = json.loads(device_name)
+                    if storage_config and hasattr(storage_config, "tp_rank"):
+                        tp_rank = storage_config.tp_rank
+                        # Try both integer and string keys since JSON parsing may convert keys
+                        device_name = device_config.get(tp_rank, "")
+                        if not device_name:
+                            device_name = device_config.get(str(tp_rank), "")
+                    else:
+                        device_name = ""
+                except (json.JSONDecodeError, AttributeError):
+                    logger.warning(
+                        f"Failed to parse device_name as JSON: {device_name}"
+                    )
+                    device_name = ""
+
             ret_code = self.store.setup(
                 self.config.local_hostname,
                 self.config.metadata_server,
                 per_tp_global_segment_size,
                 per_tp_local_buffer_size,
                 self.config.protocol,
-                self.config.device_name,
+                device_name,
                 self.config.master_server_address,
             )
             if ret_code: