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net: ethtool: add support for symmetric-xor RSS hash

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Symmetric RSS hash functions are beneficial in applications that monitor
both Tx and Rx packets of the same flow (IDS, software firewalls, ..etc).
Getting all traffic of the same flow on the same RX queue results in
higher CPU cache efficiency.

A NIC that supports "symmetric-xor" can achieve this RSS hash symmetry
by XORing the source and destination fields and pass the values to the
RSS hash algorithm.

The user may request RSS hash symmetry for a specific algorithm, via:

    # ethtool -X eth0 hfunc <hash_alg> symmetric-xor

or turn symmetry off (asymmetric) by:

    # ethtool -X eth0 hfunc <hash_alg>

The specific fields for each flow type should then be specified as usual
via:
    # ethtool -N|-U eth0 rx-flow-hash <flow_type> s|d|f|n

Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Ahmed Zaki <ahmed.zaki@intel.com>
Link: https://lore.kernel.org/r/20231213003321.605376-4-ahmed.zaki@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Ahmed Zaki
2023-12-12 17:33:16 -07:00
committed by Jakub Kicinski
parent dcd8dbf9e7
commit 13e59344fb
8 changed files with 74 additions and 6 deletions
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15
Documentation/networking/scaling.rst
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@@ -44,6 +44,21 @@ by masking out the low order seven bits of the computed hash for the
packet (usually a Toeplitz hash), taking this number as a key into the
indirection table and reading the corresponding value.
Some NICs support symmetric RSS hashing where, if the IP (source address,
destination address) and TCP/UDP (source port, destination port) tuples
are swapped, the computed hash is the same. This is beneficial in some
applications that monitor TCP/IP flows (IDS, firewalls, ...etc) and need
both directions of the flow to land on the same Rx queue (and CPU). The
"Symmetric-XOR" is a type of RSS algorithms that achieves this hash
symmetry by XORing the input source and destination fields of the IP
and/or L4 protocols. This, however, results in reduced input entropy and
could potentially be exploited. Specifically, the algorithm XORs the input
as follows::
# (SRC_IP ^ DST_IP, SRC_IP ^ DST_IP, SRC_PORT ^ DST_PORT, SRC_PORT ^ DST_PORT)
The result is then fed to the underlying RSS algorithm.
Some advanced NICs allow steering packets to queues based on
programmable filters. For example, webserver bound TCP port 80 packets
can be directed to their own receive queue. Such “n-tuple” filters can