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

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Message-ID: <CAF=yD-Jt_Tx-gsCy0ygxm8Wgx_6bxbbi3+4NgjULqQ9gK-xang@mail.gmail.com>
Date:   Sun, 21 Oct 2018 16:05:34 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        steffen.klassert@...unet.com
Subject: Re: [RFC PATCH v2 00/10] udp: implement GRO support

On Fri, Oct 19, 2018 at 10:30 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> 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.

> 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.