ovpn: preserve GSO and GRO batching

Hi,

This series is a reworked version of my earlier RFC exploring how ovpn can preserve GSO and GRO batching across its data path. Since sending the RFC, I spent more time profiling the paths on different systems and refining the implementation. The result is a smaller series with some additional optimizations and a fresh set of measurements.

On transmit, it lets GSO skbs reach ovpn, completes each inner packet's checksum during software segmentation and, when the layout permits, encrypts the resulting packets directly into a UDP GSO aggregate. Ordinary packets and frag-list GSO children retain the existing in-place encryption path. Packet IDs for a UDP GSO batch are reserved as a single range instead of one segment at a time.

On receive, ovpn uses UDP GRO to collect compatible DATA_V2 records in a frag-list, then detaches and authenticates each record independently. Small transmit and receive prefetch changes use the resulting lookahead to overlap memory access with encryption and decryption.

On two directly connected 100-Gbit/s mlx5 ports, five interleaved iperf3 -t 60 -O 10 single-flow AES-128-GCM runs in each direction raised mean throughput from 12.053 to 24.166 Gbit/s forward and from 10.992 to 23.558 Gbit/s reverse. Individual patch messages contain the intermediate measurements and test details.

Thanks,

Ralf Lici
Mandelbit Srl

---
Changes since RFC v4 https://lore.kernel.org/openvpn-devel/[email protected]/
- Drop the opt-in direct GRO mode and the generic GRO ownership change
it required. The series now retains the complete outer receive stack.
- Preserve safe page-backed payload fragments during GSO segmentation
and map them directly into the AEAD source scatterlist.
- Reserve one consecutive packet-ID range for each UDP GSO batch instead
of updating the counter once per segment.
- Extend transmit prefetch to the first payload fragment of segments
encrypted into a UDP GSO aggregate.
- Refresh the GSO, GRO and prefetch measurements using two directly
connected 100-Gbit/s mlx5 ports.

Ralf Lici (8):
ovpn: advertise checksum offload for GSO packets
ovpn: accept frag-list GSO input
ovpn: refactor AEAD encryption helpers
ovpn: convert GSO input into UDP GSO output
ovpn: reserve packet-ID ranges for UDP GSO batches
ovpn: coalesce UDP data records with GRO
ovpn: prefetch encrypted records before GRO batch decryption
ovpn: prefetch GSO segments before encryption

 drivers/net/ovpn/crypto_aead.c | 171 +++++++++++++----
 drivers/net/ovpn/crypto_aead.h |   4 +
 drivers/net/ovpn/io.c          | 339 ++++++++++++++++++++++++++++++---
 drivers/net/ovpn/io.h          |  18 +-
 drivers/net/ovpn/main.c        |   5 +-
 drivers/net/ovpn/pktid.h       |  48 +++++
 drivers/net/ovpn/proto.h       |   4 +
 drivers/net/ovpn/skb.h         |  27 ++-
 drivers/net/ovpn/stats.h       |  16 +-
 drivers/net/ovpn/tcp.c         |   4 +-
 drivers/net/ovpn/udp.c         | 258 ++++++++++++++++++++++++-
 net/core/gro.c                 |   1 +
 net/ipv4/udp_offload.c         |   3 +-
 13 files changed, 810 insertions(+), 88 deletions(-)

base-commit: b8e9e7d82e7eefd5d2d528469d94ec20e96b38c3

2.55.0


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