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ethernet: Add details about LRO/GRO #1390

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Apr 18, 2024
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ethernet: Add details about LRO/GRO #1390

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28 changes: 22 additions & 6 deletions docs/configuration/interfaces/ethernet.rst
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Expand Up @@ -61,6 +61,22 @@

Enable different types of hardware offloading on the given NIC.

:abbr:`LRO (Large Receive Offload)` is a technique designed to boost the
efficiency of how your computer's network interface card (NIC) processes
incoming network traffic. Typically, network data arrives in smaller chunks
called packets. Processing each packet individually consumes CPU (central
processing unit) resources. Lots of small packets can lead to a performance
bottleneck. Instead of handing the CPU each packet as it comes in, LRO
instructs the NIC to combine multiple incoming packets into a single, larger
packet. This larger packet is then passed to the CPU for processing.

.. note:: Under some circumstances, LRO is known to modify the packet headers
of forwarded traffic, which breaks the end-to-end principle of computer
networking. LRO is also only able to offload TCP segments encapsulated in
IPv4 packets. Due to these limitations, it is recommended to use GRO
(Generic Receive Offload) where possible. More information on the
limitations of LRO can be found here: https://lwn.net/Articles/358910/

:abbr:`GSO (Generic Segmentation Offload)` is a pure software offload that is
meant to deal with cases where device drivers cannot perform the offloads
described above. What occurs in GSO is that a given skbuff will have its data
Expand All @@ -87,13 +103,13 @@
placing the packet on the desired CPU's backlog queue and waking up the CPU
for processing. RPS has some advantages over RSS:

- it can be used with any NIC,
- software filters can easily be added to hash over new protocols,
- it does not increase hardware device interrupt rate (although it does
introduce inter-processor interrupts (IPIs)).
- it can be used with any NIC
- software filters can easily be added to hash over new protocols
- it does not increase hardware device interrupt rate, although it does
introduce inter-processor interrupts (IPIs)

.. note:: In order to use TSO/LRO with VMXNET3 adaters one must also enable
the SG offloading option.
.. note:: In order to use TSO/LRO with VMXNET3 adapters, the SG offloading
option must also be enabled.

Authentication (EAPoL)
----------------------
Expand Down Expand Up @@ -274,3 +290,3 @@

.. stop_vyoslinter

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