[PD] Skip `tp_size` exchange with rank0 (#19413)

Signed-off-by: NickLucche <nlucches@redhat.com>

tests/v1/kv_connector/unit/test_nixl_connector.py

@@ -7,6 +7,8 @@ from collections import defaultdict
 from typing import Optional
 from unittest.mock import patch
 
+import pytest
+
 from vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector import (
     KVConnectorRole, NixlAgentMetadata, NixlConnector, NixlConnectorMetadata,
     NixlConnectorWorker)
@@ -161,7 +163,8 @@ class FakeNixlConnectorWorker(NixlConnectorWorker):
         super().__init__(*args, **kwargs)
         self._hand_shake_latency = hand_shake_latency
 
-    def _nixl_handshake(self, host: str, port: int) -> dict[int, str]:
+    def _nixl_handshake(self, host: str, port: int,
+                        remote_tp_size: int) -> dict[int, str]:
         # Mimic slow _nixl_handshake, as well as bypass zmq communication.
         time.sleep(self._hand_shake_latency)
         # These should've been done in register_kv_caches(), called by
@@ -177,10 +180,10 @@ class FakeNixlConnectorWorker(NixlConnectorWorker):
                 agent_metadata=FakeNixlWrapper.AGENT_METADATA,
                 kv_caches_base_addr=[0],
                 num_blocks=1,
-                tp_size=1,
                 block_len=self.block_len,
                 attn_backend_name=self.backend_name,
-            ))
+            ),
+            remote_tp_size=remote_tp_size)
         return {0: remote_agent_name}
 
 
@@ -233,6 +236,8 @@ class TestNixlHandshake:
                         "localhost",
                         "remote_port":
                         1234,
+                        "remote_tp_size":
+                        1,
                     })
             connector.bind_connector_metadata(metadata)
 
@@ -259,13 +264,23 @@ class TestNixlHandshake:
     @patch(
         "vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector.NixlWrapper",
         FakeNixlWrapper)
+    @pytest.mark.parametrize("decode_tp_size, prefill_tp_size", [
+        (1, 1),
+        (2, 1),
+        (4, 2),
+        (4, 4),
+    ])
     def test_async_load_kv(
             self,
-        # dist_init is a fixture that initializes the distributed environment.
-        dist_init):
+            # Fixture that initializes the distributed environment.
+            dist_init,
+            # Simulate consumer-producer TP sizes.
+            decode_tp_size,
+            prefill_tp_size):
         """Test that NixlConnector's start_load_kv should be non-blocking."""
 
         vllm_config = create_vllm_config()
+        vllm_config.parallel_config.tensor_parallel_size = decode_tp_size
 
         # Test worker role in decode server.
         connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
@@ -280,6 +295,7 @@ class TestNixlHandshake:
                                  FakeNixlConnectorWorker.REMOTE_ENGINE_ID,
                                  "remote_host": "localhost",
                                  "remote_port": 1234,
+                                 "remote_tp_size": prefill_tp_size,
                              })
         connector.bind_connector_metadata(metadata)
 
@@ -329,6 +345,7 @@ class TestNixlHandshake:
                                      FakeNixlConnectorWorker.REMOTE_ENGINE_ID,
                                      "remote_host": "localhost",
                                      "remote_port": 1234,
+                                     "remote_tp_size": 1,
                                  })
         connector.bind_connector_metadata(metadata)
 

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

@@ -62,7 +62,6 @@ class NixlAgentMetadata(
     agent_metadata: bytes
     kv_caches_base_addr: list[int]
     num_blocks: int
-    tp_size: int
     block_len: int
     attn_backend_name: str
 
@@ -73,7 +72,8 @@ class ReqMeta:
     remote_block_ids: list[int]
     remote_host: str
     remote_port: int
-    remote_engine_id: EngineId
+    remote_engine_id: str
+    tp_size: int
 
 
 class NixlConnectorMetadata(KVConnectorMetadata):
@@ -93,6 +93,8 @@ class NixlConnectorMetadata(KVConnectorMetadata):
             remote_engine_id=kv_transfer_params["remote_engine_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.
+            tp_size=kv_transfer_params.get("tp_size", 1),
         )
 
 
@@ -330,7 +332,7 @@ class NixlConnectorScheduler:
             remote_engine_id=self.engine_id,
             remote_host=self.side_channel_host,
             remote_port=self.side_channel_port,
-        )
+            tp_size=self.vllm_config.parallel_config.tensor_parallel_size)
 
 
 class NixlConnectorWorker:
@@ -473,7 +475,8 @@ class NixlConnectorWorker:
                         "Connection listener got unexpected message %s", msg)
                 sock.send_multipart((identity, b"", encoded_data))
 
-    def _nixl_handshake(self, host: str, port: int) -> dict[int, str]:
+    def _nixl_handshake(self, host: str, port: int,
+                        remote_tp_size: int) -> dict[int, str]:
         """Do a NIXL handshake with a remote instance."""
 
         start_time = time.perf_counter()
@@ -482,7 +485,7 @@ class NixlConnectorWorker:
         # a hack to keep us moving. We will switch when moving to etcd
         # or where we have a single ZMQ socket in the scheduler.
 
-        def handshake(path: str, rank: int) -> tuple[NixlAgentMetadata, str]:
+        def handshake(path: str, rank: int) -> str:
             # Send query for the request.
             with zmq_ctx(zmq.REQ, path) as sock:
                 sock.send(GET_META_MSG)
@@ -492,33 +495,25 @@ class NixlConnectorWorker:
                 got_metadata_time = time.perf_counter()
 
                 # Register Remote agent.
-                remote_agent_name = self.add_remote_agent(metadata, rank)
+                remote_agent_name = self.add_remote_agent(
+                    metadata, rank, remote_tp_size)
                 setup_agent_time = time.perf_counter()
 
                 logger.debug("NIXL handshake: get metadata took: %s",
                              got_metadata_time - start_time)
                 logger.debug("NIXL handshake: add agent took: %s",
                              setup_agent_time - got_metadata_time)
-                return metadata, remote_agent_name
-
-        # Handshake with remote agent-rank0 first to get the tp_size of remote
-        path = make_zmq_path("tcp", host, port)
-        logger.debug("Querying master rank metadata on path: %s", path)
-        rank_to_agent_name: dict[int, str] = {}
-        metadata, rank_to_agent_name[0] = handshake(path, 0)
+                return remote_agent_name
 
-        # Handshake only with the other TP remote the current local rank will
+        # Handshake only with the remote TP rank that current local rank will
         # pull from. With homogeneous TP it happens to be the same rank_i.
-        tp_ratio = self._tp_size[self.engine_id] // metadata.tp_size
+        tp_ratio = self._tp_size[self.engine_id] // remote_tp_size
         p_remote_rank = self.tp_rank // tp_ratio
-        if p_remote_rank > 0:
         path = make_zmq_path("tcp", host, port + p_remote_rank)
-            logger.debug("Querying metadata on path: %s at remote rank %s",
-                         path, p_remote_rank)
-            _, rank_to_agent_name[p_remote_rank] = handshake(
-                path, p_remote_rank)
-
-        return rank_to_agent_name
+        logger.debug("Querying metadata on path: %s at remote rank %s", path,
+                     p_remote_rank)
+        # Remote rank -> agent name.
+        return {p_remote_rank: handshake(path, p_remote_rank)}
 
     def register_kv_caches(self, kv_caches: dict[str, torch.Tensor]):
         """Register the KV Cache data in nixl."""
@@ -645,7 +640,6 @@ class NixlConnectorWorker:
             agent_metadata=self.nixl_wrapper.get_agent_metadata(),
             kv_caches_base_addr=self.kv_caches_base_addr[self.engine_id],
             num_blocks=self.num_blocks,
-            tp_size=self.world_size,
             block_len=self.block_len,
             attn_backend_name=self.backend_name)
         ready_event = threading.Event()
@@ -659,7 +653,8 @@ class NixlConnectorWorker:
 
     def add_remote_agent(self,
                          nixl_agent_meta: NixlAgentMetadata,
-                         remote_tp_rank: int = 0) -> str:
+                         remote_tp_rank: int = 0,
+                         remote_tp_size: int = 1) -> str:
         """
         Add the remote NIXL agent and prepare the descriptors for reading cache
         blocks from remote.
@@ -704,9 +699,9 @@ class NixlConnectorWorker:
             return self._remote_agents[engine_id][remote_tp_rank]
 
         if engine_id in self._tp_size:
-            assert self._tp_size[engine_id] == nixl_agent_meta.tp_size
+            assert self._tp_size[engine_id] == remote_tp_size
         else:
-            self._tp_size[engine_id] = nixl_agent_meta.tp_size
+            self._tp_size[engine_id] = remote_tp_size
         # We may eventually enable this after asserting equality in cache
         # layout and close outputs.
         assert nixl_agent_meta.attn_backend_name == self.backend_name
@@ -756,9 +751,7 @@ class NixlConnectorWorker:
         # rank. With heterogeneous TP, prepare the descriptors by splitting the
         # P KV cache along kv_head dim, of D worker's kv_head size (D>P).
         # Eg. PTP1 DTP2 => P0 KV:[block0-KV_0 | block0-KV_1..].
-        p_remote_tp_rank = self.tp_rank // tp_ratio
         # Only register the remote's descriptors if current rank pulls from it.
-        if p_remote_tp_rank == remote_tp_rank:
         self.kv_caches_base_addr[
             engine_id] = nixl_agent_meta.kv_caches_base_addr
         rank_offset = self.tp_rank % tp_ratio * self.block_len \
@@ -917,7 +910,7 @@ class NixlConnectorWorker:
                         if fut is None:
                             fut = self._handshake_initiation_executor.submit(
                                 self._nixl_handshake, meta.remote_host,
-                                meta.remote_port)
+                                meta.remote_port, meta.tp_size)
                             self._handshake_futures[remote_engine_id] = fut
 
                             def done_callback(f: Future[dict[int, str]],
@@ -957,13 +950,9 @@ class NixlConnectorWorker:
             remote_block_ids=meta.remote_block_ids,
         )
 
-    def _read_blocks(
-        self,
-        local_block_ids: list[int],
-        remote_block_ids: list[int],
-        dst_engine_id: str,
-        request_id: str,
-    ):
+    def _read_blocks(self, local_block_ids: list[int],
+                     remote_block_ids: list[int], dst_engine_id: str,
+                     request_id: str):
         # NOTE(rob): having the staging blocks be on the READER side is
         # not going to work well (since we will have to call rearrange tensors).
         # after we detect the txn is complete (which means we cannot make the