[PATCH net v2 4/4] selftests: net: Fix slow configurations in big_tcp_tunnels.sh
From: Alice Mikityanska <hidden>
Date: 2026-08-22 12:03:38
Also in:
linux-kselftest
Subsystem:
kernel selftest framework, networking [general], the rest · Maintainers:
Shuah Khan, Shuah Khan, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Alice Mikityanska <redacted>
The combination of checksum offload disabled (that causes software GSO)
and a debug kernel 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.
Fixes: 5cb53743e1ff ("selftests: net: Add a test for BIG TCP in UDP tunnels")
Signed-off-by: Alice Mikityanska <redacted>
---
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 003878df7415..cc0875e52fb9 100755
--- a/tools/testing/selftests/net/big_tcp_tunnels.sh
+++ b/tools/testing/selftests/net/big_tcp_tunnels.sh@@ -49,6 +49,8 @@ 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() {
@@ -135,6 +137,21 @@ do_test() { IPTABLES_SACK=ip6tables fi + if [ "$3" != 'on' ] && [ "$KSFT_MACHINE_SLOW" = yes ]; 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