selftests/net: calibrate txtimestamp

The test sends packets and compares enqueue, transmit and Ack
timestamps with expected values. It installs netem delays to increase
latency between these points.

The test proves flaky in virtual environment (vng). Increase the
delays to reduce variance. Scale measurement tolerance accordingly.

Time sensitive tests are difficult to calibrate. Increasing delays 10x
also increases runtime 10x, for one. And it may still prove flaky at
some rate.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240127023212.3746239-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/txtimestamp.sh

@@ -8,13 +8,13 @@ set -e
 
 setup() {
 	# set 1ms delay on lo egress
-	tc qdisc add dev lo root netem delay 1ms
+	tc qdisc add dev lo root netem delay 10ms
 
 	# set 2ms delay on ifb0 egress
 	modprobe ifb
 	ip link add ifb_netem0 type ifb
 	ip link set dev ifb_netem0 up
-	tc qdisc add dev ifb_netem0 root netem delay 2ms
+	tc qdisc add dev ifb_netem0 root netem delay 20ms
 
 	# redirect lo ingress through ifb0 egress
 	tc qdisc add dev lo handle ffff: ingress
@@ -24,9 +24,11 @@ setup() {
 }
 
 run_test_v4v6() {
-	# SND will be delayed 1000us
-	# ACK will be delayed 6000us: 1 + 2 ms round-trip
-	local -r args="$@ -v 1000 -V 6000"
+	# SND will be delayed 10ms
+	# ACK will be delayed 60ms: 10 + 20 ms round-trip
+	# allow +/- tolerance of 8ms
+	# wait for ACK to be queued
+	local -r args="$@ -v 10000 -V 60000 -t 8000 -S 80000"
 
 	./txtimestamp ${args} -4 -L 127.0.0.1
 	./txtimestamp ${args} -6 -L ::1