[PATCH net-next 4/4] selftests: net: Fix slow configurations in big_tcp_tunnels.sh

[Alice Mikityanska <alice.kernel@fastmail.im>]

From: Alice Mikityanska <alice@isovalent.com>

The combination of checksum offload disabled (that causes software GSO)
and CONFIG_DEBUG_NET=y is inherently slow. Depending on the CPU power
and load, RTT may increase, limiting sk_pacing_rate, so tcp_tso_autosize
caps SKBs at around 40 segments, and zero BIG TCP packets are produced.

Increase sysctl net.ipv4.tcp_min_tso_segs and set a bigger initial value
of CWND in these configurations to force BIG TCP.

Signed-off-by: Alice Mikityanska <alice@isovalent.com>
---
 tools/testing/selftests/net/big_tcp_tunnels.sh | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tools/testing/selftests/net/big_tcp_tunnels.sh b/tools/testing/selftests/net/big_tcp_tunnels.sh
index 1f1c811c563c..222de7c0c294 100755
--- a/tools/testing/selftests/net/big_tcp_tunnels.sh
+++ b/tools/testing/selftests/net/big_tcp_tunnels.sh
@@ -56,6 +56,8 @@ setup() {
 
 	ip netns exec "$SERVER_NS" netserver >/dev/null
 	wait_local_port_listen "$SERVER_NS" 12865 tcp
+
+	DEFAULT_TCP_MIN_TSO_SEGS=$(ip netns exec "$CLIENT_NS" sysctl -n net.ipv4.tcp_min_tso_segs)
 }
 
 setup_tunnel() {
@@ -142,6 +144,21 @@ do_test() {
 		IPTABLES_SACK=ip6tables
 	fi
 
+	if [ "$3" != 'on' ] && is_debug; then
+		echo 'Slow configuration; increasing net.ipv4.tcp_min_tso_segs and initcwnd'
+		ip netns exec "$CLIENT_NS" sysctl -w net.ipv4.tcp_min_tso_segs=52
+		if [ "$2" = 4 ]; then
+			ip -netns "$CLIENT_NS" \
+			    route change 192.168.2.0/24 dev tun0 initcwnd 100
+		else
+			ip -netns "$CLIENT_NS" -6 \
+			    route change 2001:db8::2:0/112 dev tun0 initcwnd 100
+		fi
+	else
+		ip netns exec "$CLIENT_NS" \
+		    sysctl -w net.ipv4.tcp_min_tso_segs="$DEFAULT_TCP_MIN_TSO_SEGS"
+	fi
+
 	ip netns exec "$SERVER_NS" "$IPTABLES" -w -t raw -I PREROUTING -i "${CAPTURE_IFACE}1" -m length ! --length 0:65535 -m comment --comment "bigtcp"
 	ip netns exec "$CLIENT_NS" "$IPTABLES" -w -t raw -I OUTPUT -o "${CAPTURE_IFACE}0" -m length ! --length 0:65535 -m comment --comment "bigtcp"
 	ip netns exec "$SERVER_NS" "$IPTABLES_SACK" -w -t raw -I OUTPUT -o "tun1" -p tcp -m tcp --tcp-flags ACK ACK --tcp-option 5 -m comment --comment "sack"
-- 
2.55.0