From dc170da3347e0f7b6d120d13882c4e1f04ca00d6 Mon Sep 17 00:00:00 2001 From: Alice Mikityanska Date: Sat, 22 Aug 2026 15:03:05 +0300 Subject: [PATCH 1/4] selftests: net: Wait for netserver to launch Use wait_local_port_listen after starting netserver in big_tcp_tunnels.sh to ensure it's listening when the test starts. Fixes: 5cb53743e1ff ("selftests: net: Add a test for BIG TCP in UDP tunnels") Signed-off-by: Alice Mikityanska Acked-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260822120308.1165200-2-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski --- tools/testing/selftests/net/big_tcp_tunnels.sh | 3 +++ 1 file changed, 3 insertions(+) diff --git a/tools/testing/selftests/net/big_tcp_tunnels.sh b/tools/testing/selftests/net/big_tcp_tunnels.sh index d6513ed8d4e8..9b7d0456bcc1 100755 --- a/tools/testing/selftests/net/big_tcp_tunnels.sh +++ b/tools/testing/selftests/net/big_tcp_tunnels.sh @@ -3,6 +3,8 @@ # # Testing for IPv4 and IPv6 BIG TCP over VXLAN and GENEVE tunnels. +source "$(dirname "$0")/lib.sh" + SERVER_NS=$(mktemp -u server-XXXXXXXX) SERVER_IP4="192.168.1.1" SERVER_IP6="2001:db8::1:1" @@ -39,6 +41,7 @@ setup() { gro_max_size 196608 gro_ipv4_max_size 196608 ip netns exec "$SERVER_NS" netserver >/dev/null + wait_local_port_listen "$SERVER_NS" 12865 tcp } setup_tunnel() { From bb42c16f489f10144f7d2fbb1f57753f14e12ac8 Mon Sep 17 00:00:00 2001 From: Alice Mikityanska Date: Sat, 22 Aug 2026 15:03:06 +0300 Subject: [PATCH 2/4] selftests: net: Lower threshold on debug kernels for big_tcp_tunnels.sh Debug kernels on upstream CI runners run slower and generate fewer BIG TCP packets, making the test flaky on upstream CI runners. Lower the default threshold for those kernels. Fixes: 5cb53743e1ff ("selftests: net: Add a test for BIG TCP in UDP tunnels") Signed-off-by: Alice Mikityanska Acked-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260822120308.1165200-3-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski --- tools/testing/selftests/net/big_tcp_tunnels.sh | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/net/big_tcp_tunnels.sh b/tools/testing/selftests/net/big_tcp_tunnels.sh index 9b7d0456bcc1..e0b41f394ebb 100755 --- a/tools/testing/selftests/net/big_tcp_tunnels.sh +++ b/tools/testing/selftests/net/big_tcp_tunnels.sh @@ -17,11 +17,18 @@ CLIENT_IP6="2001:db8::1:2" CLIENT_IP4_TUN="192.168.2.2" CLIENT_IP6_TUN="2001:db8::2:2" -: "${PACKETS_THRESHOLD:=1000}" - # Kselftest framework requirement - SKIP code is 4. ksft_skip=4 +if [ -z "$PACKETS_THRESHOLD" ]; then + if [ "$KSFT_MACHINE_SLOW" = yes ]; then + echo 'Debug kernel detected, lowering the default threshold' + PACKETS_THRESHOLD=100 + else + PACKETS_THRESHOLD=1000 + fi +fi + setup() { ip netns add "$SERVER_NS" ip netns add "$CLIENT_NS" From f7d0400bd3452ed6915592b1929ba1d39d8e6552 Mon Sep 17 00:00:00 2001 From: Alice Mikityanska Date: Sat, 22 Aug 2026 15:03:07 +0300 Subject: [PATCH 3/4] selftests: net: Lower threshold with csum offload off in big_tcp_tunnels.sh With checksum offload disabled, much fewer BIG TCP packets are generated due to overall loss of throughput. Use a separate threshold in these tests, which is 1/10 of the threshold set for the rest of tests. Fixes: 5cb53743e1ff ("selftests: net: Add a test for BIG TCP in UDP tunnels") Signed-off-by: Alice Mikityanska Acked-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260822120308.1165200-4-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski --- tools/testing/selftests/net/big_tcp_tunnels.sh | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/net/big_tcp_tunnels.sh b/tools/testing/selftests/net/big_tcp_tunnels.sh index e0b41f394ebb..003878df7415 100755 --- a/tools/testing/selftests/net/big_tcp_tunnels.sh +++ b/tools/testing/selftests/net/big_tcp_tunnels.sh @@ -107,6 +107,8 @@ cleanup() { } do_test() { + local packets_threshold="$PACKETS_THRESHOLD" + # When tx csum offload is off, software GSO is performed before passing the # packet to veth. Check BIG TCP packets inside the VXLAN tunnel to verify # the software checksum path: if the checksum code is broken, these packets @@ -125,6 +127,7 @@ do_test() { else IPTABLES=ip6tables fi + packets_threshold=$(( PACKETS_THRESHOLD / 10 )) fi if [ "$2" = 4 ]; then IPTABLES_SACK=iptables @@ -157,8 +160,8 @@ do_test() { echo "Captured BIG TCP RX packets: $PACKETS_SERVER" echo "Captured BIG TCP TX packets: $PACKETS_CLIENT" echo "Captured TCP SACK packets: $PACKETS_SACK" - [ "$PACKETS_SERVER" -gt "$PACKETS_THRESHOLD" ] || return 1 - [ "$PACKETS_CLIENT" -gt "$PACKETS_THRESHOLD" ] || return 1 + [ "$PACKETS_SERVER" -gt "$packets_threshold" ] || return 1 + [ "$PACKETS_CLIENT" -gt "$packets_threshold" ] || return 1 [ "$PACKETS_SACK" -lt "$(( PACKETS_CLIENT / 2 ))" ] || return 1 } From 1d62b83fb75125344693db8ebf970653db529f40 Mon Sep 17 00:00:00 2001 From: Alice Mikityanska Date: Sat, 22 Aug 2026 15:03:08 +0300 Subject: [PATCH 4/4] selftests: net: Fix slow configurations in big_tcp_tunnels.sh The combination of checksum offload disabled (that causes software GSO) and a debug kernel is inherently slow. Depending on the CPU power and load, RTT may increase, limiting sk_pacing_rate, so tcp_tso_autosize caps SKBs at around 40 segments, and zero BIG TCP packets are produced. Increase sysctl net.ipv4.tcp_min_tso_segs and set a bigger initial value of CWND in these configurations to force BIG TCP. Fixes: 5cb53743e1ff ("selftests: net: Add a test for BIG TCP in UDP tunnels") Signed-off-by: Alice Mikityanska Acked-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260822120308.1165200-5-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski --- tools/testing/selftests/net/big_tcp_tunnels.sh | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/tools/testing/selftests/net/big_tcp_tunnels.sh b/tools/testing/selftests/net/big_tcp_tunnels.sh index 003878df7415..cc0875e52fb9 100755 --- a/tools/testing/selftests/net/big_tcp_tunnels.sh +++ b/tools/testing/selftests/net/big_tcp_tunnels.sh @@ -49,6 +49,8 @@ setup() { ip netns exec "$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"