Re: [RFC PATCH v2 00/10] udp: implement GRO support

Hi all,

On Sun, 2018-10-21 at 16:05 -0400, Willem de Bruijn wrote:

On Fri, Oct 19, 2018 at 10:30 AM Paolo Abeni [off-list ref] wrote:

quoted

This series implements GRO support for UDP sockets, as the RX counterpart
of commit bec1f6f69736 ("udp: generate gso with UDP_SEGMENT").
The core functionality is implemented by the second patch, introducing a new
sockopt to enable UDP_GRO, while patch 3 implements support for passing the
segment size to the user space via a new cmsg.
UDP GRO performs a socket lookup for each ingress packets and aggregate datagram
directed to UDP GRO enabled sockets with constant l4 tuple.

UDP GRO packets can land on non GRO-enabled sockets, e.g. due to iptables NAT
rules, and that could potentially confuse existing applications.

Good catch.

quoted

The solution adopted here is to de-segment the GRO packet before enqueuing
as needed. Since we must cope with packet reinsertion after de-segmentation,
the relevant code is factored-out in ipv4 and ipv6 specific helpers and exposed
to UDP usage.

While the current code can probably be improved, this safeguard ,implemented in
the patches 4-7, allows future enachements to enable UDP GSO offload on more
virtual devices eventually even on forwarded packets.

The last 4 for patches implement some performance and functional self-tests,
re-using the existing udpgso infrastructure. The problematic scenario described
above is explicitly tested.

This looks awesome! Impressive testing, too.

A few comments in the individual patches, mostly minor.

Thank you for the in-depth review! (in the WE ;)

I'll try to address the comments on each patch individually.

In the end I rushed a bit this RFC, because the misdirection issue (and
the tentative fix) bothered me more than a bit: I wanted to check I was
not completely out-of-track.

Cheers,

Paolo