[KVConnector][Metrics] Aggregate scheduler-side KVConnectorStats (#26046)

Signed-off-by: Qier Li <kevin44036@gmail.com>

tests/v1/kv_connector/unit/test_nixl_connector.py

@@ -839,6 +839,75 @@ def test_multi_kv_connector_stats_aggregation():
     assert kv_connector_stats["FooConnector"].data["num_foo_transfers"] == 6
 
 
+@patch(
+    "vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector.NixlWrapper",
+    FakeNixlWrapper,
+)
+def test_scheduler_kv_connector_stats_aggregation():
+    """Test scheduler and worker KV connector stats aggregation."""
+    from vllm.v1.core.sched.output import SchedulerOutput
+
+    scheduler = create_scheduler(create_vllm_config())
+
+    # Worker stats with transfer metrics
+    worker_stats = NixlKVConnectorStats()
+    worker_stats.record_transfer(get_default_xfer_telemetry())
+    worker_stats.data["remote_tokens"] = []
+
+    # Scheduler stats with custom metric (needs dummy transfer to avoid being skipped)
+    scheduler_stats = NixlKVConnectorStats()
+    scheduler_stats.data.update(
+        {  # dummy transfer just for testing, to bypass is_empty() check
+            "transfer_duration": [0],
+            "post_duration": [0],
+            "bytes_transferred": [0],
+            "num_descriptors": [0],
+            "remote_tokens": [128],
+        }
+    )
+
+    # Mock the scheduler connector's stats method
+    scheduler.connector.get_kv_connector_stats = lambda: MultiKVConnectorStats(
+        data={"NixlConnector": scheduler_stats}
+    )
+
+    model_output = ModelRunnerOutput(
+        req_ids=["req_0"],
+        req_id_to_index={"req_0": 0},
+        sampled_token_ids=[[123]],
+        logprobs=None,
+        prompt_logprobs_dict={},
+        pooler_output=[None],
+        kv_connector_output=KVConnectorOutput(
+            kv_connector_stats=MultiKVConnectorStats(
+                data={"NixlConnector": worker_stats}
+            )
+        ),
+    )
+    scheduler_output = SchedulerOutput(
+        scheduled_new_reqs=[],
+        scheduled_cached_reqs=None,
+        num_scheduled_tokens={"req_0": 1},
+        total_num_scheduled_tokens=1,
+        scheduled_spec_decode_tokens={},
+        scheduled_encoder_inputs={},
+        num_common_prefix_blocks=[0],
+        finished_req_ids=set(),
+        free_encoder_mm_hashes=set(),
+        structured_output_request_ids={},
+        grammar_bitmask=None,
+    )
+
+    engine_core_outputs = scheduler.update_from_output(scheduler_output, model_output)
+
+    final_stats = next(
+        iter(engine_core_outputs.values())
+    ).scheduler_stats.kv_connector_stats
+    nixl_stats = final_stats["NixlConnector"]
+    assert nixl_stats.num_successful_transfers == 2
+    assert nixl_stats.data["remote_tokens"] == [128]
+
+
 @pytest.mark.parametrize("distributed_executor_backend", ["ray", None])
 @patch(
     "vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector.NixlWrapper",

vllm/v1/core/sched/scheduler.py

@@ -924,6 +924,10 @@ class Scheduler(SchedulerInterface):
         kv_connector_stats = (
             kv_connector_output.kv_connector_stats if kv_connector_output else None
         )
+        if kv_connector_stats and self.connector:
+            stats = self.connector.get_kv_connector_stats()
+            if stats:
+                kv_connector_stats = kv_connector_stats.aggregate(stats)
 
         failed_kv_load_req_ids = None
         if kv_connector_output and kv_connector_output.invalid_block_ids: