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Paolo Abeni says:
====================
geneve: introduce double tunnel GSO/GRO support
This is the [belated] incarnation of topic discussed in the last Neconf
[1].
In container orchestration in virtual environments there is a consistent
usage of double UDP tunneling - specifically geneve. Such setup lack
support of GRO and GSO for inter VM traffic.
After commit b430f6c38d ("Merge branch 'virtio_udp_tunnel_08_07_2025'
of https://github.com/pabeni/linux-devel") and the qemu cunter-part, VMs
are able to send/receive GSO over UDP aggregated packets.
This series introduces the missing bit for full end-to-end aggregation
in the above mentioned scenario. Specifically:
- introduces a new netdev feature set to generalize existing per device
driver GSO admission check.1
- adds GSO partial support for the geneve and vxlan drivers
- introduces and use a geneve option to assist double tunnel GRO
- adds some simple functional tests for the above.
The new device features set is not strictly needed for the following
work, but avoids the introduction of trivial `ndo_features_check` to
support GSO partial and thus possible performance regression due to the
additional indirect call. Such feature set could be leveraged by a
number of existing drivers (intel, meta and possibly wangxun) to avoid
duplicate code/tests. Such part has been omitted here to keep the series
small.
Both GSO partial support and double GRO support have some downsides.
With the first in place, GSO partial packets will traverse the network
stack 'downstream' the outer geneve UDP tunnel and will be visible by
the udp/IP/IPv6 and by netfilter. Currently only H/W NICs implement GSO
partial support and such packets are visible only via software taps.
Double UDP tunnel GRO will cook 'GSO partial' like aggregate packets,
i.e. the inner UDP encapsulation headers set will still carry the
wire-level lengths and csum, so that segmentation considering such
headers parts of a giant, constant encapsulation header will yield the
correct result.
The correct GSO packet layout is applied when the packet traverse the
outermost geneve encapsulation.
Both GSO partial and double UDP encap are disabled by default and must
be explicitly enabled via, respectively ethtool and geneve device
configuration.
Finally note that the GSO partial feature could potentially be applied
to all the other UDP tunnels, but this series limits its usage to geneve
and vxlan devices.
Link: https://netdev.bots.linux.dev/netconf/2024/paolo.pdf [1]
====================
Link: https://patch.msgid.link/cover.1769011015.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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