Merge branch 'net-introduce-rps_default_mask'

Paolo Abeni says:

====================
net: introduce rps_default_mask

Real-time setups try hard to ensure proper isolation between time
critical applications and e.g. network processing performed by the
network stack in softirq and RPS is used to move the softirq
activity away from the isolated core.

If the network configuration is dynamic, with netns and devices
routinely created at run-time, enforcing the correct RPS setting
on each newly created device allowing to transient bad configuration
became complex.

Additionally, when multi-queue devices are involved, configuring rps
in user-space on each queue easily becomes very expensive, e.g.
some setups use veths with per cpu queues.

These series try to address the above, introducing a new
sysctl knob: rps_default_mask. The new sysctl entry allows
configuring a netns-wide RPS mask, to be enforced since receive
queue creation time without any fourther per device configuration
required.

Additionally, a simple self-test is introduced to check the
rps_default_mask behavior.
====================

Link: https://lore.kernel.org/r/cover.1675789134.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 61 insertions, 0 deletions

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 951bd5342bc6..3364c548a23b 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -46,6 +46,7 @@ TEST_PROGS += stress_reuseport_listen.sh
 TEST_PROGS += l2_tos_ttl_inherit.sh
 TEST_PROGS += bind_bhash.sh
 TEST_PROGS += ip_local_port_range.sh
+TEST_PROGS += rps_default_mask.sh
 TEST_PROGS_EXTENDED := in_netns.sh setup_loopback.sh setup_veth.sh
 TEST_PROGS_EXTENDED += toeplitz_client.sh toeplitz.sh
 TEST_GEN_FILES =  socket nettest
diff --git a/tools/testing/selftests/net/config b/tools/testing/selftests/net/config
index bd89198cd817..cc9fd55ab869 100644
--- a/tools/testing/selftests/net/config
+++ b/tools/testing/selftests/net/config
@@ -3,6 +3,9 @@ CONFIG_NET_NS=y
 CONFIG_BPF_SYSCALL=y
 CONFIG_TEST_BPF=m
 CONFIG_NUMA=y
+CONFIG_RPS=y
+CONFIG_SYSFS=y
+CONFIG_PROC_SYSCTL=y
 CONFIG_NET_VRF=y
 CONFIG_NET_L3_MASTER_DEV=y
 CONFIG_IPV6=y
diff --git a/tools/testing/selftests/net/rps_default_mask.sh b/tools/testing/selftests/net/rps_default_mask.sh
new file mode 100755
index 000000000000..c81c0ac7ddfe
--- /dev/null
+++ b/tools/testing/selftests/net/rps_default_mask.sh
@@ -0,0 +1,57 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+readonly ksft_skip=4
+readonly cpus=$(nproc)
+ret=0
+
+[ $cpus -gt 2 ] || exit $ksft_skip
+
+readonly INITIAL_RPS_DEFAULT_MASK=$(cat /proc/sys/net/core/rps_default_mask)
+readonly NETNS="ns-$(mktemp -u XXXXXX)"
+
+setup() {
+	ip netns add "${NETNS}"
+	ip -netns "${NETNS}" link set lo up
+}
+
+cleanup() {
+	echo $INITIAL_RPS_DEFAULT_MASK > /proc/sys/net/core/rps_default_mask
+	ip netns del $NETNS
+}
+
+chk_rps() {
+	local rps_mask expected_rps_mask=$3
+	local dev_name=$2
+	local msg=$1
+
+	rps_mask=$(ip netns exec $NETNS cat /sys/class/net/$dev_name/queues/rx-0/rps_cpus)
+	printf "%-60s" "$msg"
+	if [ $rps_mask -eq $expected_rps_mask ]; then
+		echo "[ ok ]"
+	else
+		echo "[fail] expected $expected_rps_mask found $rps_mask"
+		ret=1
+	fi
+}
+
+trap cleanup EXIT
+
+echo 0 > /proc/sys/net/core/rps_default_mask
+setup
+chk_rps "empty rps_default_mask" lo 0
+cleanup
+
+echo 1 > /proc/sys/net/core/rps_default_mask
+setup
+chk_rps "non zero rps_default_mask" lo 1
+
+echo 3 > /proc/sys/net/core/rps_default_mask
+chk_rps "changing rps_default_mask dont affect existing netns" lo 1
+
+ip -n $NETNS link add type veth
+ip -n $NETNS link set dev veth0 up
+ip -n $NETNS link set dev veth1 up
+chk_rps "changing rps_default_mask affect newly created devices" veth0 3
+chk_rps "changing rps_default_mask affect newly created devices[II]" veth1 3
+exit $ret