selftests/bpf: Add XDP load-balancer benchmark run script

Add a convenience script that runs all 24 XDP load-balancer scenarios
and formats the results as a table with median, stddev, and p99
columns.

  ./benchs/run_bench_xdp_lb.sh

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20260427232313.1582588-8-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/benchs/run_bench_xdp_lb.sh

@@ -0,0 +1,79 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+source ./benchs/run_common.sh
+
+set -eufo pipefail
+
+WARMUP=${WARMUP:-3}
+
+RUN="sudo ./bench -q -w${WARMUP} -a xdp-lb --machine-readable"
+
+SEP="  +----------------------------------+----------+---------+----------+"
+HDR="  | %-32s | %8s | %7s | %8s |\n"
+ROW="  | %-32s | %8s | %7s | %8s |\n"
+
+function group_header()
+{
+	printf "%s\n" "$SEP"
+	printf "$HDR" "$1" "p50" "stddev" "p99"
+	printf "%s\n" "$SEP"
+}
+
+function rval()
+{
+	echo "$1" | sed -nE "s/.*$2=([^ ]+).*/\1/p"
+}
+
+function run_scenario()
+{
+	local sc="$1"
+	shift
+	local output rline
+
+	output=$($RUN --scenario "$sc" "$@" 2>&1) || true
+	rline=$(echo "$output" | grep '^RESULT ' || true)
+
+	if [ -z "$rline" ]; then
+		printf "$ROW" "$sc" "ERR" "-" "-"
+		return
+	fi
+
+	printf "$ROW" "$sc" \
+		"$(rval "$rline" median)" \
+		"$(rval "$rline" stddev)" \
+		"$(rval "$rline" p99)"
+}
+
+header "XDP load-balancer benchmark"
+
+group_header "Single-flow baseline"
+for sc in tcp-v4-lru-hit tcp-v4-ch \
+	  tcp-v6-lru-hit tcp-v6-ch \
+	  udp-v4-lru-hit udp-v6-lru-hit \
+	  tcp-v4v6-lru-hit; do
+	run_scenario "$sc"
+done
+
+group_header "Diverse flows (4K src addrs)"
+for sc in tcp-v4-lru-diverse tcp-v4-ch-diverse \
+	  tcp-v6-lru-diverse tcp-v6-ch-diverse \
+	  udp-v4-lru-diverse; do
+	run_scenario "$sc"
+done
+
+group_header "TCP flags"
+run_scenario tcp-v4-syn
+run_scenario tcp-v4-rst-miss
+
+group_header "LRU stress"
+run_scenario tcp-v4-lru-miss
+run_scenario udp-v4-lru-miss
+run_scenario tcp-v4-lru-warmup
+
+group_header "Early exits"
+for sc in pass-v4-no-vip pass-v6-no-vip pass-v4-icmp pass-non-ip drop-v4-frag drop-v4-options \
+	  drop-v6-frag; do
+	run_scenario "$sc"
+done
+printf "%s\n" "$SEP"