Fix RDMA device mapping for non-zero GPU indices in disaggregation tests (#21303)

Co-authored-by: Alison Shao <alison.shao@MacBook-Pro-D2W773R9CD.local>
Co-authored-by: hnyls2002 <lsyincs@gmail.com>

python/sglang/srt/server_args.py

@@ -3234,9 +3234,15 @@ class ServerArgs:
         if len(devices) == 0:
             raise ValueError("No valid IB devices specified")
 
-        # Check for duplicates
+        # Deduplicate while preserving order
-        if len(devices) != len(set(devices)):
+        unique_devices = list(dict.fromkeys(devices))
-            raise ValueError(f"Duplicate IB devices specified: {device_str}")
+        if len(unique_devices) != len(devices):
+            logger.warning(
+                "Duplicate IB devices specified: %s. Deduplicating to: %s",
+                device_str,
+                ",".join(unique_devices),
+            )
+            devices = unique_devices
 
         # Get available IB devices from sysfs
         ib_sysfs_path = "/sys/class/infiniband"

python/sglang/test/server_fixtures/disaggregation_fixture.py

@@ -249,11 +249,13 @@ def get_rdma_devices_args():
     )
 
     rdma_devices = []
+    base_gpu = min(gpu_indices)
     for gpu_idx in gpu_indices:
-        nic_index = min(gpu_idx // gpus_per_rdma, n_rdma - 1)
+        nic_index = min((gpu_idx - base_gpu) // gpus_per_rdma, n_rdma - 1)
         rdma_devices.append(rdma_all_devices[nic_index])
 
     if not rdma_devices:
         return ",".join(_pick_default_pair(rdma_all_devices))
 
-    return ",".join(rdma_devices)
+    # Deduplicate while preserving order
+    return ",".join(dict.fromkeys(rdma_devices))