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.

These series try to address the above, introducing a new sysctl knob: rps_default_mask. The new sysctl entry allows configuring a systemwide 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.

v1 -> v2:
- fix sparse warning in patch 2/3

Paolo Abeni (3):
net/sysctl: factor-out netdev_rx_queue_set_rps_mask() helper net/core: introduce default_rps_mask netns attribute
self-tests: introduce self-tests for RPS default mask

 Documentation/admin-guide/sysctl/net.rst      |  6 ++
 include/linux/netdevice.h                     |  1 +
 net/core/net-sysfs.c                          | 73 +++++++++++--------
 net/core/sysctl_net_core.c                    | 58 +++++++++++++++
 tools/testing/selftests/net/Makefile          |  1 +
 tools/testing/selftests/net/config            |  3 +
 .../testing/selftests/net/rps_default_mask.sh | 57 +++++++++++++++
 7 files changed, 169 insertions(+), 30 deletions(-)
 create mode 100755 tools/testing/selftests/net/rps_default_mask.sh

2.26.2