feat(agentic): route B200 DEP traffic through native vLLM router

Author: cquil11

benchmarks/single_node/agentic/dsv4_fp4_b200_vllm.sh

@@ -55,11 +55,28 @@ nvidia-smi
 resolve_trace_source
 install_agentic_deps
 
+# vllm-project/router expands the one HTTP backend into one logical worker per
+# DP rank and sends X-data-parallel-rank on forwarded requests. aiperf's
+# X-Correlation-ID is stable for every turn of a conversation; alias it to the
+# router's preferred X-Session-ID header.
+USE_VLLM_ROUTER=false
+VLLM_BACKEND_PORT="$PORT"
+if [ "$DP_ATTENTION" = "true" ]; then
+    USE_VLLM_ROUTER=true
+    VLLM_BACKEND_PORT=$((PORT + 1))
+    VLLM_ROUTER_VERSION=0.1.14
+    VLLM_ROUTER_POLICY=consistent_hash
+    VLLM_ROUTER_METRICS_PORT=$((PORT + 10000))
+    export AIPERF_HTTP_X_SESSION_ID_FROM_CORRELATION_ID=1
+    agentic_pip_install --quiet "vllm-router==$VLLM_ROUTER_VERSION"
+fi
+
 # DeepSeek-V4-Pro weights are large; engine startup can exceed default 600s.
 export VLLM_ENGINE_READY_TIMEOUT_S=3600
 
 # ---- Server config ----------------------------------------------------------
 SERVER_LOG="$RESULT_DIR/server.log"
+ROUTER_LOG="$RESULT_DIR/router.log"
 LMCACHE_LOG="$RESULT_DIR/lmcache_server.log"
 mkdir -p "$RESULT_DIR"
 
@@ -233,7 +250,7 @@ export VLLM_FLOAT32_MATMUL_PRECISION=high
 VLLM_CMD=(
     vllm serve "$MODEL_PATH" --served-model-name "$MODEL"
     --host 0.0.0.0
-    --port "$PORT"
+    --port "$VLLM_BACKEND_PORT"
     --trust-remote-code
     --kv-cache-dtype fp8
     --block-size 256
@@ -257,7 +274,23 @@ printf '\n' | tee -a "$RESULT_DIR/vllm_command.txt"
 SERVER_PID=$!
 echo "Server PID: $SERVER_PID"
 
-wait_for_server_ready --port "$PORT" --server-log "$SERVER_LOG" --server-pid "$SERVER_PID"
+wait_for_server_ready --port "$VLLM_BACKEND_PORT" --server-log "$SERVER_LOG" --server-pid "$SERVER_PID"
+
+if [ "$USE_VLLM_ROUTER" = "true" ]; then
+    echo "Starting native vLLM router on port $PORT for $TP DP ranks..."
+    vllm-router \
+        --worker-urls "http://localhost:$VLLM_BACKEND_PORT" \
+        --policy "$VLLM_ROUTER_POLICY" \
+        --intra-node-data-parallel-size "$TP" \
+        --host 0.0.0.0 \
+        --port "$PORT" \
+        --prometheus-host 127.0.0.1 \
+        --prometheus-port "$VLLM_ROUTER_METRICS_PORT" \
+        --disable-retries > "$ROUTER_LOG" 2>&1 &
+    ROUTER_PID=$!
+    echo "Router PID: $ROUTER_PID"
+    wait_for_server_ready --port "$PORT" --server-log "$ROUTER_LOG" --server-pid "$ROUTER_PID"
+fi
 
 # ---- Run benchmark ----------------------------------------------------------
 build_replay_cmd "$RESULT_DIR"