[PATCH net-next 0/5] net: ethtool: make netdev_rss_key_fill() spread flows over all queues

[Eric Dumazet <edumazet@google.com>]

netdev_rss_key_fill() hands drivers a uniformly random key. Because the
Toeplitz hash is linear over GF(2), a random key is singular for a given
header field and queue count with probability 1/2: flows differing only
in the low order bits of that field (such as a burst of consecutive
ephemeral ports) then cannot reach all RX queues. On one affected 16-queue
host, only 4 queues received traffic until the key was replaced.

Patch 1 synchronizes proc_do_rss_key() with netdev_rss_key_fill() using an
smp_wmb()/smp_rmb() pair and a boolean flag so readers of
/proc/sys/net/core/netdev_rss_key print zero bytes until the key is fully
populated.

Patch 2 keeps the key random but constrains 1008 of its 2048 bits so that,
at every 16-bit aligned position and for every power-of-two queue count up
to 256, consecutive values of a field ending there visit every queue once.
Applying the fixup on the 16-bit grid covers standard 2-tuple/4-tuple
hashes as well as encapsulated or bitmap-selected layouts (such as PSP
inner TCP ports at byte 78) without enumerating them in the core. The
fixup is a bijection onto the set of valid keys, and redraws in the ~1 in
5 case where two 32-bit windows a multiple of 8 bits apart alias.

Patch 3 adds a KUnit suite verifying full rank across standard and
encapsulated fields, the full 16-bit grid, window non-aliasing, and
end-to-end flow spreading.

Patches 4 and 5 add kselftests for keys on a running system: patch 4
checks /proc/sys/net/core/netdev_rss_key, and patch 5 checks the live RSS
key and indirection table reported by a device via ethtool.

Eric Dumazet (5):
  net: synchronize proc_do_rss_key() with netdev_rss_key_fill()
  net: ethtool: generate RSS keys that spread flows over all queues
  net: ethtool: add KUnit tests for the generated RSS key
  selftests: net: check the quality of the host RSS key
  selftests: drivers: net: check the RSS key a device uses

 Documentation/networking/scaling.rst          |   9 +
 net/Kconfig                                   |  14 +
 net/core/dev.h                                |   1 +
 net/core/sysctl_net_core.c                    |   7 +-
 net/ethtool/Makefile                          |   2 +
 net/ethtool/common.h                          |  11 +
 net/ethtool/ioctl.c                           | 170 +++++++++-
 net/ethtool/rss_key_test.c                    | 314 ++++++++++++++++++
 .../testing/selftests/drivers/net/hw/Makefile |   1 +
 .../drivers/net/hw/lib/py/__init__.py         |   5 +
 .../selftests/drivers/net/hw/rss_key.py       | 172 ++++++++++
 tools/testing/selftests/net/Makefile          |   1 +
 .../testing/selftests/net/lib/py/__init__.py  |   5 +
 tools/testing/selftests/net/lib/py/rsskey.py  | 108 ++++++
 tools/testing/selftests/net/netdev_rss_key.py | 117 +++++++
 15 files changed, 935 insertions(+), 2 deletions(-)
 create mode 100644 net/ethtool/rss_key_test.c
 create mode 100755 tools/testing/selftests/drivers/net/hw/rss_key.py
 create mode 100644 tools/testing/selftests/net/lib/py/rsskey.py
 create mode 100755 tools/testing/selftests/net/netdev_rss_key.py

-- 
2.55.0.1082.g2b9226bbc0-goog