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selftests: net: Fix slow configurations in big_tcp_tunnels.sh

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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: 5cb53743e1 ("selftests: net: Add a test for BIG TCP in UDP tunnels")
Signed-off-by: Alice Mikityanska <alice@isovalent.com>
Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260822120308.1165200-5-alice.kernel@fastmail.im
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Alice Mikityanska
2026-08-22 15:03:08 +03:00
committed by Jakub Kicinski
parent f7d0400bd3
commit 1d62b83fb7
1 changed files with 17 additions and 0 deletions
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17
tools/testing/selftests/net/big_tcp_tunnels.sh
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@@ -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"