net-test: add TCP CUBIC congestion control tests

Add TCP CUBIC congestion control tests. We have been running these
tests for a while to test CUBIC behavior.

These tests were originally written by Neal Cardwell, maintained by
the Google TCP and kernel networking teams, and ported to upstream
kernels by Shuo Chen and Neal Cardwell.

Signed-off-by: Neal Cardwell <[email protected]>
Signed-off-by: Shuo Chen <[email protected]>

gtests/net/tcp/cubic/cubic-bulk-166k-idle-restart.pkt

@@ -0,0 +1,111 @@
+// Test bulk CUBIC flow at 166 kbit/sec (2 1000-byte payloads each 100ms
+// means 2 * 1040 * 8 / .1 = 166400 bits/sec).
+// This variant checks to see if CUBIC grows its cwnd unreasonably
+// due to crediting itself for time accumulated in an idle state.
+
+// For this test We mostly just care about cwnd values, not exact timing.
+// So to reduce flakes allow ~20ms of timing variation:
+--tolerance_usecs=20000
+
+`../../common/defaults.sh
+tc qdisc replace dev tun0 root fq
+sysctl -q net.ipv4.tcp_congestion_control=cubic
+sysctl -q net.ipv4.tcp_min_tso_segs=4
+# Disable TLP to avoid flakes from spurious retransmits:
+sysctl -q net.ipv4.tcp_early_retrans=0`
+
+// Initialize connection
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 10>
+   +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 8>
+  +.1 < . 1:1(0) ack 1 win 514
+
+   +0 accept(3, ..., ...) = 4
+
+   +0 setsockopt(4, SOL_SOCKET, SO_SNDBUF, [2000000], 4) = 0
+   +0 %{ assert tcpi_snd_cwnd == 10, tcpi_snd_cwnd }%
+   +0 write(4, ..., 40000) = 40000
+
+  +.1 < .  1:1(0) ack 2001 win 514
+  +.1 < .  1:1(0) ack 4001 win 514
+  +.1 < .  1:1(0) ack 6001 win 514
+  +.1 < .  1:1(0) ack 8001 win 514
+  +.1 < .  1:1(0) ack 10001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 20, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 12001 win 514
+  +.1 < .  1:1(0) ack 14001 win 514
+  +.1 < .  1:1(0) ack 16001 win 514
+  +.1 < .  1:1(0) ack 18001 win 514
+  +.1 < .  1:1(0) ack 20001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 30, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 22001 win 514
+  +.1 < .  1:1(0) ack 24001 win 514
+  +.1 < .  1:1(0) ack 26001 win 514
+  +.1 < .  1:1(0) ack 28001 win 514
+  +.1 < .  1:1(0) ack 30001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 40, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 32001 win 514
+  +.1 < .  1:1(0) ack 34001 win 514
+  +.1 < .  1:1(0) ack 36001 win 514
+  +.1 < .  1:1(0) ack 38001 win 514
+// Hystart exits slow start here at a cwnd of 48:
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 48, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 40001 win 514
+
+// Go idle for a while in order to verify that this doesn't let us
+// accumulate "credit" toward increasing cwnd quickly when we go
+// cwnd-limited again.
+   +4 write(4, ..., 160000) = 160000
+
+  +.1 < .  1:1(0) ack 42001 win 514
+  +.1 < .  1:1(0) ack 44001 win 514
+  +.1 < .  1:1(0) ack 46001 win 514
+  +.1 < .  1:1(0) ack 48001 win 514
+  +.1 < .  1:1(0) ack 50001 win 514
+  +.1 < .  1:1(0) ack 52001 win 514
+  +.1 < .  1:1(0) ack 54001 win 514
+  +.1 < .  1:1(0) ack 56001 win 514
+  +.1 < .  1:1(0) ack 58001 win 514
+  +.1 < .  1:1(0) ack 60001 win 514
+   +0 %{ print(tcpi_snd_cwnd);  assert tcpi_snd_cwnd == 48, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 62001 win 514
+  +.1 < .  1:1(0) ack 64001 win 514
+  +.1 < .  1:1(0) ack 66001 win 514
+  +.1 < .  1:1(0) ack 68001 win 514
+  +.1 < .  1:1(0) ack 70001 win 514
+  +.1 < .  1:1(0) ack 72001 win 514
+  +.1 < .  1:1(0) ack 74001 win 514
+  +.1 < .  1:1(0) ack 76001 win 514
+  +.1 < .  1:1(0) ack 78001 win 514
+  +.1 < .  1:1(0) ack 80001 win 514
+   +0 %{ print(tcpi_snd_cwnd);  assert tcpi_snd_cwnd == 49, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 82001 win 514
+  +.1 < .  1:1(0) ack 84001 win 514
+  +.1 < .  1:1(0) ack 86001 win 514
+  +.1 < .  1:1(0) ack 88001 win 514
+  +.1 < .  1:1(0) ack 90001 win 514
+  +.1 < .  1:1(0) ack 92001 win 514
+  +.1 < .  1:1(0) ack 94001 win 514
+  +.1 < .  1:1(0) ack 96001 win 514
+  +.1 < .  1:1(0) ack 98001 win 514
+  +.1 < .  1:1(0) ack 100001 win 514
+   +0 %{ print(tcpi_snd_cwnd);  assert tcpi_snd_cwnd == 52, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 102001 win 514
+  +.1 < .  1:1(0) ack 104001 win 514
+  +.1 < .  1:1(0) ack 106001 win 514
+  +.1 < .  1:1(0) ack 108001 win 514
+  +.1 < .  1:1(0) ack 110001 win 514
+  +.1 < .  1:1(0) ack 112001 win 514
+  +.1 < .  1:1(0) ack 114001 win 514
+  +.1 < .  1:1(0) ack 116001 win 514
+  +.1 < .  1:1(0) ack 118001 win 514
+  +.1 < .  1:1(0) ack 120001 win 514
+   +0 %{ print(tcpi_snd_cwnd);  assert tcpi_snd_cwnd == 58, tcpi_snd_cwnd }%

gtests/net/tcp/cubic/cubic-bulk-166k.pkt

@@ -0,0 +1,287 @@
+// Test bulk CUBIC flow at 166 kbit/sec (2 1000-byte payloads each 100ms
+// means 2 * 1040 * 8 / .1 = 166400 bits/sec).
+// Verifies that CUBIC increases its cwnd by at most 1 packet
+// for every 2 packets ACKed.
+// Also tests the CUBIC Hystart algorithm for exiting slow start.
+
+// For this test We mostly just care about cwnd values, not exact timing.
+// So to reduce flakes allow ~20ms of timing variation:
+--tolerance_usecs=20000
+
+`../../common/defaults.sh
+tc qdisc replace dev tun0 root fq
+sysctl -q net.ipv4.tcp_congestion_control=cubic
+sysctl -q net.ipv4.tcp_min_tso_segs=4
+# Disable TLP to avoid flakes from spurious retransmits:
+sysctl -q net.ipv4.tcp_early_retrans=0`
+
+// Initialize connection
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 10>
+   +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 8>
+  +.1 < . 1:1(0) ack 1 win 514
+
+   +0 accept(3, ..., ...) = 4
+
+// SO_SNDBUF is doubled, so we can write the full amount below:
+   +0 setsockopt(4, SOL_SOCKET, SO_SNDBUF, [200000], 4) = 0
+   +0 %{ assert tcpi_snd_cwnd == 10, tcpi_snd_cwnd }%
+   +0 write(4, ..., 400000) = 400000
+
+  +.1 < .  1:1(0) ack 2001 win 514
+  +.1 < .  1:1(0) ack 4001 win 514
+  +.1 < .  1:1(0) ack 6001 win 514
+  +.1 < .  1:1(0) ack 8001 win 514
+  +.1 < .  1:1(0) ack 10001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 20, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 12001 win 514
+  +.1 < .  1:1(0) ack 14001 win 514
+  +.1 < .  1:1(0) ack 16001 win 514
+  +.1 < .  1:1(0) ack 18001 win 514
+  +.1 < .  1:1(0) ack 20001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 30, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 22001 win 514
+  +.1 < .  1:1(0) ack 24001 win 514
+  +.1 < .  1:1(0) ack 26001 win 514
+  +.1 < .  1:1(0) ack 28001 win 514
+  +.1 < .  1:1(0) ack 30001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 40, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 32001 win 514
+  +.1 < .  1:1(0) ack 34001 win 514
+  +.1 < .  1:1(0) ack 36001 win 514
+  +.1 < .  1:1(0) ack 38001 win 514
+// Hystart exits slow start here at a cwnd of 48:
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 48, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 40001 win 514
+  +.1 < .  1:1(0) ack 42001 win 514
+  +.1 < .  1:1(0) ack 44001 win 514
+  +.1 < .  1:1(0) ack 46001 win 514
+  +.1 < .  1:1(0) ack 48001 win 514
+  +.1 < .  1:1(0) ack 50001 win 514
+  +.1 < .  1:1(0) ack 52001 win 514
+  +.1 < .  1:1(0) ack 54001 win 514
+  +.1 < .  1:1(0) ack 56001 win 514
+  +.1 < .  1:1(0) ack 58001 win 514
+  +.1 < .  1:1(0) ack 60001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 49, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 62001 win 514
+  +.1 < .  1:1(0) ack 64001 win 514
+  +.1 < .  1:1(0) ack 66001 win 514
+  +.1 < .  1:1(0) ack 68001 win 514
+  +.1 < .  1:1(0) ack 70001 win 514
+  +.1 < .  1:1(0) ack 72001 win 514
+  +.1 < .  1:1(0) ack 74001 win 514
+  +.1 < .  1:1(0) ack 76001 win 514
+  +.1 < .  1:1(0) ack 78001 win 514
+  +.1 < .  1:1(0) ack 80001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 50, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 82001 win 514
+  +.1 < .  1:1(0) ack 84001 win 514
+  +.1 < .  1:1(0) ack 86001 win 514
+  +.1 < .  1:1(0) ack 88001 win 514
+  +.1 < .  1:1(0) ack 90001 win 514
+  +.1 < .  1:1(0) ack 92001 win 514
+  +.1 < .  1:1(0) ack 94001 win 514
+  +.1 < .  1:1(0) ack 96001 win 514
+  +.1 < .  1:1(0) ack 98001 win 514
+  +.1 < .  1:1(0) ack 100001 win 514
+   +0 %{ print(tcpi_snd_cwnd); assert tcpi_snd_cwnd == 52, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 102001 win 514
+  +.1 < .  1:1(0) ack 104001 win 514
+  +.1 < .  1:1(0) ack 106001 win 514
+  +.1 < .  1:1(0) ack 108001 win 514
+  +.1 < .  1:1(0) ack 110001 win 514
+  +.1 < .  1:1(0) ack 112001 win 514
+  +.1 < .  1:1(0) ack 114001 win 514
+  +.1 < .  1:1(0) ack 116001 win 514
+  +.1 < .  1:1(0) ack 118001 win 514
+  +.1 < .  1:1(0) ack 120001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd = 58; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+// From this point onward, we verify that for every 2 packets ACKed,
+// CUBIC increases its cwnd by 1 packet.
+  +.1 < .  1:1(0) ack 122001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 124001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 126001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 128001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 130001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 132001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 134001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 136001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 138001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+  +.1 < .  1:1(0) ack 140001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 1; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 142001 win 514
+  +.1 < .  1:1(0) ack 144001 win 514
+  +.1 < .  1:1(0) ack 146001 win 514
+  +.1 < .  1:1(0) ack 148001 win 514
+  +.1 < .  1:1(0) ack 150001 win 514
+  +.1 < .  1:1(0) ack 152001 win 514
+  +.1 < .  1:1(0) ack 154001 win 514
+  +.1 < .  1:1(0) ack 156001 win 514
+  +.1 < .  1:1(0) ack 158001 win 514
+  +.1 < .  1:1(0) ack 160001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 162001 win 514
+  +.1 < .  1:1(0) ack 164001 win 514
+  +.1 < .  1:1(0) ack 166001 win 514
+  +.1 < .  1:1(0) ack 168001 win 514
+  +.1 < .  1:1(0) ack 170001 win 514
+  +.1 < .  1:1(0) ack 172001 win 514
+  +.1 < .  1:1(0) ack 174001 win 514
+  +.1 < .  1:1(0) ack 176001 win 514
+  +.1 < .  1:1(0) ack 178001 win 514
+  +.1 < .  1:1(0) ack 180001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 182001 win 514
+  +.1 < .  1:1(0) ack 184001 win 514
+  +.1 < .  1:1(0) ack 186001 win 514
+  +.1 < .  1:1(0) ack 188001 win 514
+  +.1 < .  1:1(0) ack 190001 win 514
+  +.1 < .  1:1(0) ack 192001 win 514
+  +.1 < .  1:1(0) ack 194001 win 514
+  +.1 < .  1:1(0) ack 196001 win 514
+  +.1 < .  1:1(0) ack 198001 win 514
+  +.1 < .  1:1(0) ack 200001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 202001 win 514
+  +.1 < .  1:1(0) ack 204001 win 514
+  +.1 < .  1:1(0) ack 206001 win 514
+  +.1 < .  1:1(0) ack 208001 win 514
+  +.1 < .  1:1(0) ack 210001 win 514
+  +.1 < .  1:1(0) ack 212001 win 514
+  +.1 < .  1:1(0) ack 214001 win 514
+  +.1 < .  1:1(0) ack 216001 win 514
+  +.1 < .  1:1(0) ack 218001 win 514
+  +.1 < .  1:1(0) ack 220001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 222001 win 514
+  +.1 < .  1:1(0) ack 224001 win 514
+  +.1 < .  1:1(0) ack 226001 win 514
+  +.1 < .  1:1(0) ack 228001 win 514
+  +.1 < .  1:1(0) ack 230001 win 514
+  +.1 < .  1:1(0) ack 232001 win 514
+  +.1 < .  1:1(0) ack 234001 win 514
+  +.1 < .  1:1(0) ack 236001 win 514
+  +.1 < .  1:1(0) ack 238001 win 514
+  +.1 < .  1:1(0) ack 240001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 242001 win 514
+  +.1 < .  1:1(0) ack 244001 win 514
+  +.1 < .  1:1(0) ack 246001 win 514
+  +.1 < .  1:1(0) ack 248001 win 514
+  +.1 < .  1:1(0) ack 250001 win 514
+  +.1 < .  1:1(0) ack 252001 win 514
+  +.1 < .  1:1(0) ack 254001 win 514
+  +.1 < .  1:1(0) ack 256001 win 514
+  +.1 < .  1:1(0) ack 258001 win 514
+  +.1 < .  1:1(0) ack 260001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 262001 win 514
+  +.1 < .  1:1(0) ack 264001 win 514
+  +.1 < .  1:1(0) ack 266001 win 514
+  +.1 < .  1:1(0) ack 268001 win 514
+  +.1 < .  1:1(0) ack 270001 win 514
+  +.1 < .  1:1(0) ack 272001 win 514
+  +.1 < .  1:1(0) ack 274001 win 514
+  +.1 < .  1:1(0) ack 276001 win 514
+  +.1 < .  1:1(0) ack 278001 win 514
+  +.1 < .  1:1(0) ack 280001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 282001 win 514
+  +.1 < .  1:1(0) ack 284001 win 514
+  +.1 < .  1:1(0) ack 286001 win 514
+  +.1 < .  1:1(0) ack 288001 win 514
+  +.1 < .  1:1(0) ack 290001 win 514
+  +.1 < .  1:1(0) ack 292001 win 514
+  +.1 < .  1:1(0) ack 294001 win 514
+  +.1 < .  1:1(0) ack 296001 win 514
+  +.1 < .  1:1(0) ack 298001 win 514
+  +.1 < .  1:1(0) ack 300001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 302001 win 514
+  +.1 < .  1:1(0) ack 304001 win 514
+  +.1 < .  1:1(0) ack 306001 win 514
+  +.1 < .  1:1(0) ack 308001 win 514
+  +.1 < .  1:1(0) ack 310001 win 514
+  +.1 < .  1:1(0) ack 312001 win 514
+  +.1 < .  1:1(0) ack 314001 win 514
+  +.1 < .  1:1(0) ack 316001 win 514
+  +.1 < .  1:1(0) ack 318001 win 514
+  +.1 < .  1:1(0) ack 320001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 322001 win 514
+  +.1 < .  1:1(0) ack 324001 win 514
+  +.1 < .  1:1(0) ack 326001 win 514
+  +.1 < .  1:1(0) ack 328001 win 514
+  +.1 < .  1:1(0) ack 330001 win 514
+  +.1 < .  1:1(0) ack 332001 win 514
+  +.1 < .  1:1(0) ack 334001 win 514
+  +.1 < .  1:1(0) ack 336001 win 514
+  +.1 < .  1:1(0) ack 338001 win 514
+  +.1 < .  1:1(0) ack 340001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 342001 win 514
+  +.1 < .  1:1(0) ack 344001 win 514
+  +.1 < .  1:1(0) ack 346001 win 514
+  +.1 < .  1:1(0) ack 348001 win 514
+  +.1 < .  1:1(0) ack 350001 win 514
+  +.1 < .  1:1(0) ack 352001 win 514
+  +.1 < .  1:1(0) ack 354001 win 514
+  +.1 < .  1:1(0) ack 356001 win 514
+  +.1 < .  1:1(0) ack 358001 win 514
+  +.1 < .  1:1(0) ack 360001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 362001 win 514
+  +.1 < .  1:1(0) ack 364001 win 514
+  +.1 < .  1:1(0) ack 366001 win 514
+  +.1 < .  1:1(0) ack 368001 win 514
+  +.1 < .  1:1(0) ack 370001 win 514
+  +.1 < .  1:1(0) ack 372001 win 514
+  +.1 < .  1:1(0) ack 374001 win 514
+  +.1 < .  1:1(0) ack 376001 win 514
+  +.1 < .  1:1(0) ack 378001 win 514
+  +.1 < .  1:1(0) ack 380001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%
+
+  +.1 < .  1:1(0) ack 382001 win 514
+  +.1 < .  1:1(0) ack 384001 win 514
+  +.1 < .  1:1(0) ack 386001 win 514
+  +.1 < .  1:1(0) ack 388001 win 514
+  +.1 < .  1:1(0) ack 390001 win 514
+  +.1 < .  1:1(0) ack 392001 win 514
+  +.1 < .  1:1(0) ack 394001 win 514
+  +.1 < .  1:1(0) ack 396001 win 514
+  +.1 < .  1:1(0) ack 398001 win 514
+  +.1 < .  1:1(0) ack 400001 win 514
+   +0 %{ print(tcpi_snd_cwnd); cwnd += 10; assert tcpi_snd_cwnd == cwnd, tcpi_snd_cwnd }%