selftests: mlxsw: Add a test for UC behavior under MC flood

A so-called "MC-aware" mode has recently been enabled in mlxsw. In
MC-aware mode, BUM traffic is handled in a special way so that when a
switch is flooded with BUM, UC performance isn't unduly impacted.
Without enablement of this mode, a stream of BUM traffic can cause
sustained UC throughput drop in excess of 99 %.

Add a test for this behavior. Compare how much UC throughput degrades as
a stream of broadcast frames floods the switch. A minimal degradation is
tolerated to cover for glitches in traffic injection performance.
Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/drivers/net/mlxsw/qos_mc_aware.sh

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# A test for switch behavior under MC overload. An issue in Spectrum chips
+# causes throughput of UC traffic to drop severely when a switch is under heavy
+# MC load. This issue can be overcome by putting the switch to MC-aware mode.
+# This test verifies that UC performance stays intact even as the switch is
+# under MC flood, and therefore that the MC-aware mode is enabled and correctly
+# configured.
+#
+# Because mlxsw throttles CPU port, the traffic can't actually reach userspace
+# at full speed. That makes it impossible to use iperf3 to simply measure the
+# throughput, because many packets (that reach $h3) don't get to the kernel at
+# all even in UDP mode (the situation is even worse in TCP mode, where one can't
+# hope to see more than a couple Mbps).
+#
+# So instead we send traffic with mausezahn and use RX ethtool counters at $h3.
+# Multicast traffic is untagged, unicast traffic is tagged with PCP 1. Therefore
+# each gets a different priority and we can use per-prio ethtool counters to
+# measure the throughput. In order to avoid prioritizing unicast traffic, prio
+# qdisc is installed on $swp3 and maps all priorities to the same band #7 (and
+# thus TC 0).
+#
+# Mausezahn can't actually saturate the links unless it's using large frames.
+# Thus we set MTU to 10K on all involved interfaces. Then both unicast and
+# multicast traffic uses 8K frames.
+#
+# +-----------------------+                +----------------------------------+
+# | H1                    |                |                               H2 |
+# |                       |                |  unicast --> + $h2.111           |
+# |                       |                |  traffic     | 192.0.2.129/28    |
+# |          multicast    |                |              | e-qos-map 0:1     |
+# |          traffic      |                |              |                   |
+# | $h1 + <-----          |                |              + $h2               |
+# +-----|-----------------+                +--------------|-------------------+
+#       |                                                 |
+# +-----|-------------------------------------------------|-------------------+
+# |     + $swp1                                           + $swp2             |
+# |     | >1Gbps                                          | >1Gbps            |
+# | +---|----------------+                     +----------|----------------+  |
+# | |   + $swp1.1        |                     |          + $swp2.111      |  |
+# | |                BR1 |             SW      | BR111                     |  |
+# | |   + $swp3.1        |                     |          + $swp3.111      |  |
+# | +---|----------------+                     +----------|----------------+  |
+# |     \_________________________________________________/                   |
+# |                                    |                                      |
+# |                                    + $swp3                                |
+# |                                    | 1Gbps bottleneck                     |
+# |                                    | prio qdisc: {0..7} -> 7              |
+# +------------------------------------|--------------------------------------+
+#                                      |
+#                                   +--|-----------------+
+#                                   |  + $h3          H3 |
+#                                   |  |                 |
+#                                   |  + $h3.111         |
+#                                   |    192.0.2.130/28  |
+#                                   +--------------------+
+
+ALL_TESTS="
+	ping_ipv4
+	test_mc_aware
+"
+
+lib_dir=$(dirname $0)/../../../net/forwarding
+
+NUM_NETIFS=6
+source $lib_dir/lib.sh
+
+h1_create()
+{
+	simple_if_init $h1
+	mtu_set $h1 10000
+}
+
+h1_destroy()
+{
+	mtu_restore $h1
+	simple_if_fini $h1
+}
+
+h2_create()
+{
+	simple_if_init $h2
+	mtu_set $h2 10000
+
+	vlan_create $h2 111 v$h2 192.0.2.129/28
+	ip link set dev $h2.111 type vlan egress-qos-map 0:1
+}
+
+h2_destroy()
+{
+	vlan_destroy $h2 111
+
+	mtu_restore $h2
+	simple_if_fini $h2
+}
+
+h3_create()
+{
+	simple_if_init $h3
+	mtu_set $h3 10000
+
+	vlan_create $h3 111 v$h3 192.0.2.130/28
+}
+
+h3_destroy()
+{
+	vlan_destroy $h3 111
+
+	mtu_restore $h3
+	simple_if_fini $h3
+}
+
+switch_create()
+{
+	ip link set dev $swp1 up
+	mtu_set $swp1 10000
+
+	ip link set dev $swp2 up
+	mtu_set $swp2 10000
+
+	ip link set dev $swp3 up
+	mtu_set $swp3 10000
+
+	vlan_create $swp2 111
+	vlan_create $swp3 111
+
+	ethtool -s $swp3 speed 1000 autoneg off
+	tc qdisc replace dev $swp3 root handle 3: \
+	   prio bands 8 priomap 7 7 7 7 7 7 7 7
+
+	ip link add name br1 type bridge vlan_filtering 0
+	ip link set dev br1 up
+	ip link set dev $swp1 master br1
+	ip link set dev $swp3 master br1
+
+	ip link add name br111 type bridge vlan_filtering 0
+	ip link set dev br111 up
+	ip link set dev $swp2.111 master br111
+	ip link set dev $swp3.111 master br111
+}
+
+switch_destroy()
+{
+	ip link del dev br111
+	ip link del dev br1
+
+	tc qdisc del dev $swp3 root handle 3:
+	ethtool -s $swp3 autoneg on
+
+	vlan_destroy $swp3 111
+	vlan_destroy $swp2 111
+
+	mtu_restore $swp3
+	ip link set dev $swp3 down
+
+	mtu_restore $swp2
+	ip link set dev $swp2 down
+
+	mtu_restore $swp1
+	ip link set dev $swp1 down
+}
+
+setup_prepare()
+{
+	h1=${NETIFS[p1]}
+	swp1=${NETIFS[p2]}
+
+	swp2=${NETIFS[p3]}
+	h2=${NETIFS[p4]}
+
+	swp3=${NETIFS[p5]}
+	h3=${NETIFS[p6]}
+
+	h3mac=$(mac_get $h3)
+
+	vrf_prepare
+
+	h1_create
+	h2_create
+	h3_create
+	switch_create
+}
+
+cleanup()
+{
+	pre_cleanup
+
+	switch_destroy
+	h3_destroy
+	h2_destroy
+	h1_destroy
+
+	vrf_cleanup
+}
+
+ping_ipv4()
+{
+	ping_test $h2 192.0.2.130
+}
+
+humanize()
+{
+	local speed=$1; shift
+
+	for unit in bps Kbps Mbps Gbps; do
+		if (($(echo "$speed < 1024" | bc))); then
+			break
+		fi
+
+		speed=$(echo "scale=1; $speed / 1024" | bc)
+	done
+
+	echo "$speed${unit}"
+}
+
+rate()
+{
+	local t0=$1; shift
+	local t1=$1; shift
+	local interval=$1; shift
+
+	echo $((8 * (t1 - t0) / interval))
+}
+
+check_rate()
+{
+	local rate=$1; shift
+	local min=$1; shift
+	local what=$1; shift
+
+	if ((rate > min)); then
+		return 0
+	fi
+
+	echo "$what $(humanize $ir) < $(humanize $min_ingress)" > /dev/stderr
+	return 1
+}
+
+measure_uc_rate()
+{
+	local what=$1; shift
+
+	local interval=10
+	local i
+	local ret=0
+
+	# Dips in performance might cause momentary ingress rate to drop below
+	# 1Gbps. That wouldn't saturate egress and MC would thus get through,
+	# seemingly winning bandwidth on account of UC. Demand at least 2Gbps
+	# average ingress rate to somewhat mitigate this.
+	local min_ingress=2147483648
+
+	mausezahn $h2.111 -p 8000 -A 192.0.2.129 -B 192.0.2.130 -c 0 \
+		-a own -b $h3mac -t udp -q &
+	sleep 1
+
+	for i in {5..0}; do
+		local t0=$(ethtool_stats_get $h3 rx_octets_prio_1)
+		local u0=$(ethtool_stats_get $swp2 rx_octets_prio_1)
+		sleep $interval
+		local t1=$(ethtool_stats_get $h3 rx_octets_prio_1)
+		local u1=$(ethtool_stats_get $swp2 rx_octets_prio_1)
+
+		local ir=$(rate $u0 $u1 $interval)
+		local er=$(rate $t0 $t1 $interval)
+
+		if check_rate $ir $min_ingress "$what ingress rate"; then
+			break
+		fi
+
+		# Fail the test if we can't get the throughput.
+		if ((i == 0)); then
+			ret=1
+		fi
+	done
+
+	# Suppress noise from killing mausezahn.
+	{ kill %% && wait; } 2>/dev/null
+
+	echo $ir $er
+	exit $ret
+}
+
+test_mc_aware()
+{
+	RET=0
+
+	local -a uc_rate
+	uc_rate=($(measure_uc_rate "UC-only"))
+	check_err $? "Could not get high enough UC-only ingress rate"
+	local ucth1=${uc_rate[1]}
+
+	mausezahn $h1 -p 8000 -c 0 -a own -b bc -t udp -q &
+
+	local d0=$(date +%s)
+	local t0=$(ethtool_stats_get $h3 rx_octets_prio_0)
+	local u0=$(ethtool_stats_get $swp1 rx_octets_prio_0)
+
+	local -a uc_rate_2
+	uc_rate_2=($(measure_uc_rate "UC+MC"))
+	check_err $? "Could not get high enough UC+MC ingress rate"
+	local ucth2=${uc_rate_2[1]}
+
+	local d1=$(date +%s)
+	local t1=$(ethtool_stats_get $h3 rx_octets_prio_0)
+	local u1=$(ethtool_stats_get $swp1 rx_octets_prio_0)
+
+	local deg=$(bc <<< "
+			scale=2
+			ret = 100 * ($ucth1 - $ucth2) / $ucth1
+			if (ret > 0) { ret } else { 0 }
+		    ")
+	check_err $(bc <<< "$deg > 10")
+
+	local interval=$((d1 - d0))
+	local mc_ir=$(rate $u0 $u1 $interval)
+	local mc_er=$(rate $t0 $t1 $interval)
+
+	# Suppress noise from killing mausezahn.
+	{ kill %% && wait; } 2>/dev/null
+
+	log_test "UC performace under MC overload"
+
+	echo "UC-only throughput  $(humanize $ucth1)"
+	echo "UC+MC throughput    $(humanize $ucth2)"
+	echo "Degradation         $deg %"
+	echo
+	echo "Full report:"
+	echo "  UC only:"
+	echo "    ingress UC throughput $(humanize ${uc_rate[0]})"
+	echo "    egress UC throughput  $(humanize ${uc_rate[1]})"
+	echo "  UC+MC:"
+	echo "    ingress UC throughput $(humanize ${uc_rate_2[0]})"
+	echo "    egress UC throughput  $(humanize ${uc_rate_2[1]})"
+	echo "    ingress MC throughput $(humanize $mc_ir)"
+	echo "    egress MC throughput  $(humanize $mc_er)"
+}
+
+trap cleanup EXIT
+
+setup_prepare
+setup_wait
+
+tests_run
+
+exit $EXIT_STATUS