[NIXL] Add remote_request_id to kv_transfer_params

Include the internal request ID that the prefill instance is
expecting the decode instance to send it in the NIXL notification.

Right now, we rely on the proxy supplying the ID via X-Request-ID
and that prefill and decode will mangle this ID in identical ways.
This is obviously quite brittle, and P should be explicit about what
ID it expects from D.

Relates to #27987 - adding a random prefix to client-provided
request IDs.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>

Author: markmc

vllm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py

@@ -118,6 +118,7 @@ class ReqMeta:
     remote_host: str
     remote_port: int
     remote_engine_id: str
+    remote_request_id: str
     tp_size: int
 
 
@@ -144,6 +145,7 @@ def add_new_req(
             local_physical_block_ids=local_block_ids,
             remote_block_ids=kv_transfer_params["remote_block_ids"],
             remote_engine_id=kv_transfer_params["remote_engine_id"],
+            remote_request_id=kv_transfer_params["remote_request_id"],
             remote_host=kv_transfer_params["remote_host"],
             remote_port=kv_transfer_params["remote_port"],
             # P workers don't need to receive tp_size from proxy here.
@@ -530,7 +532,12 @@ def update_state_after_alloc(
             if params.get("remote_block_ids"):
                 if all(
                     p in params
-                    for p in ("remote_engine_id", "remote_host", "remote_port")
+                    for p in (
+                        "remote_engine_id",
+                        "remote_request_id",
+                        "remote_host",
+                        "remote_port",
+                    )
                 ):
                     # If remote_blocks and num_external_tokens = 0, we have
                     # a full prefix cache hit on the D worker. We need to call
@@ -659,6 +666,7 @@ def request_finished(
             do_remote_decode=False,
             remote_block_ids=block_ids,
             remote_engine_id=self.engine_id,
+            remote_request_id=request.request_id,
             remote_host=self.side_channel_host,
             remote_port=self.side_channel_port,
             tp_size=self.vllm_config.parallel_config.tensor_parallel_size,
@@ -1946,6 +1954,7 @@ def _read_blocks_for_req(self, req_id: str, meta: ReqMeta):
         self._read_blocks(
             request_id=req_id,
             dst_engine_id=meta.remote_engine_id,
+            remote_request_id=meta.remote_request_id,
             local_block_ids=meta.local_physical_block_ids,
             remote_block_ids=meta.remote_block_ids,
         )
@@ -1956,6 +1965,7 @@ def _read_blocks(
         remote_block_ids: list[int],
         dst_engine_id: str,
         request_id: str,
+        remote_request_id: str,
     ):
         block_size_ratio = self.kv_topo.block_size_ratio_from_engine_id(dst_engine_id)
         if block_size_ratio > 1:
@@ -1988,7 +1998,7 @@ def _read_blocks(
         # Number of D TP workers that will read from dst P. Propagate tp_ratio
         # on notification so that dst worker can wait before freeing blocks.
         tp_ratio = self.kv_topo.tp_ratio_from_engine_id(dst_engine_id)
-        notif_id = f"{request_id}:{tp_ratio}".encode()
+        notif_id = f"{remote_request_id}:{tp_ratio}".encode()
 
         # Full prefix cache hit: do not need to read remote blocks,
         # just notify P worker that we have the blocks we need.