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docs: networking: document multi-RSS context

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There seems to be no docs for the concept of multiple RSS
contexts and how to configure it. I had to explain it three
times recently, the last one being the charm, document it.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Edward Cree <ecree.xilinx@gmail.com>
Link: https://lore.kernel.org/r/20231018010758.2382742-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
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Jakub Kicinski 2023-10-17 18:07:58 -07:00 committed by Paolo Abeni
parent 65e4f4507e
commit b91f2e13c9
1 changed files with 42 additions and 0 deletions
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Documentation/networking/scaling.rst
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@ -105,6 +105,48 @@ a separate CPU. For interrupt handling, HT has shown no benefit in
initial tests, so limit the number of queues to the number of CPU cores
in the system.
Dedicated RSS contexts
~~~~~~~~~~~~~~~~~~~~~~
Modern NICs support creating multiple co-existing RSS configurations
which are selected based on explicit matching rules. This can be very
useful when application wants to constrain the set of queues receiving
traffic for e.g. a particular destination port or IP address.
The example below shows how to direct all traffic to TCP port 22
to queues 0 and 1.
To create an additional RSS context use::
# ethtool -X eth0 hfunc toeplitz context new
New RSS context is 1
Kernel reports back the ID of the allocated context (the default, always
present RSS context has ID of 0). The new context can be queried and
modified using the same APIs as the default context::
# ethtool -x eth0 context 1
RX flow hash indirection table for eth0 with 13 RX ring(s):
0: 0 1 2 3 4 5 6 7
8: 8 9 10 11 12 0 1 2
[...]
# ethtool -X eth0 equal 2 context 1
# ethtool -x eth0 context 1
RX flow hash indirection table for eth0 with 13 RX ring(s):
0: 0 1 0 1 0 1 0 1
8: 0 1 0 1 0 1 0 1
[...]
To make use of the new context direct traffic to it using an n-tuple
filter::
# ethtool -N eth0 flow-type tcp6 dst-port 22 context 1
Added rule with ID 1023
When done, remove the context and the rule::
# ethtool -N eth0 delete 1023
# ethtool -X eth0 context 1 delete
RPS: Receive Packet Steering
============================