veth: allow GRO even without XDP

This series allows the user-space to enable GRO/NAPI on a veth device even without attaching an XDP program.

It does not change the default veth behavior (no NAPI, no GRO), except that the GRO feature bit on top of this series will be effectively off by default on veth devices. Note that currently the GRO bit is on by default, but GRO never takes place in absence of XDP.

On top of this series, setting the GRO feature bit enables NAPI and allows the GRO to take place. The TSO features on the peer device are preserved.

The main goal is improving UDP forwarding performances for containers in a typical virtual network setup:

(container) veth -> veth peer -> bridge/ovs -> vxlan -> NIC

Enabling the NAPI threaded mode, GRO the NETIF_F_GRO_UDP_FWD feature on the veth peer improves the UDP stream performance with not void netfilter configuration by 2x factor with no measurable overhead for TCP traffic: some heuristic ensures that TCP will not go through the additional NAPI/GRO layer.

Some self-tests are added to check the expected behavior in the default configuration, with XDP and with plain GRO enabled.

Paolo Abeni (4):
veth: use skb_orphan_partial instead of skb_orphan
veth: allow enabling NAPI even without XDP
veth: refine napi usage
self-tests: add veth tests

 drivers/net/veth.c                   | 152 ++++++++++++++++++++---
 tools/testing/selftests/net/Makefile |   1 +
 tools/testing/selftests/net/veth.sh  | 177 +++++++++++++++++++++++++++
 3 files changed, 316 insertions(+), 14 deletions(-)
 create mode 100755 tools/testing/selftests/net/veth.sh

2.26.2