netdev - Re: [PATCH net v4] net: xdp: account for layer 3 packets in generic skb handler

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Message-ID: <CAHmME9rbRrdV0ePxT0DgurGdEKOWiEi5mH5Wtg=aJwSA6fxwMg@mail.gmail.com>
Date:   Fri, 14 Aug 2020 08:56:48 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Netdev <netdev@...r.kernel.org>,
        Thomas Ptacek <thomas@...kpuppet.org>,
        Adhipati Blambangan <adhipati@...a.io>,
        David Ahern <dsahern@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH net v4] net: xdp: account for layer 3 packets in generic
 skb handler

On Thu, Aug 13, 2020 at 11:01 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > I had originally dropped this patch, but the issue kept coming up in
> > user reports, so here's a v4 of it. Testing of it is still rather slim,
> > but hopefully that will change in the coming days.
>
> Here an alternative patch, untested:

Funny. But come on now... Why would we want to deprive our users of
system consistency?

Doesn't it make sense to allow users to use the same code across
interfaces? You actually want them to rewrite their code to use a
totally different trigger point just because of some weird kernel
internals between interfaces?

Why not make XDP more useful and more generic across interfaces? It's
very common for systems to be receiving packets with a heavy ethernet
card from the current data center, in addition to receiving packets
from a tunnel interface connected to a remote data center, with a need
to run the same XDP program on both interfaces. Why not support that
kind of simplicity?

This is _actually_ something that's come up _repeatedly_. This is a
real world need from real users who are doing real things. Why not
help them?

It's not at the expense of any formal consistency, or performance, or
even semantic perfection. It costs very little to support these
popular use cases.

[FYI, there's one tweak I'd like to make, so I'll probably send v5 ~soon.]

Jason