netdev - Re: [PATCH net-next 2/4] veth: allow enabling NAPI even without XDP

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Date:   Fri, 09 Apr 2021 16:58:55 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Toshiaki Makita <toshiaki.makita1@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>
Subject: Re: [PATCH net-next 2/4] veth: allow enabling NAPI even without XDP

Paolo Abeni <pabeni@...hat.com> writes:

> Currently the veth device has the GRO feature bit set, even if
> no GRO aggregation is possible with the default configuration,
> as the veth device does not hook into the GRO engine.
>
> Flipping the GRO feature bit from user-space is a no-op, unless
> XDP is enabled. In such scenario GRO could actually take place, but
> TSO is forced to off on the peer device.
>
> This change allow user-space to really control the GRO feature, with
> no need for an XDP program.
>
> The GRO feature bit is now cleared by default - so that there are no
> user-visible behavior changes with the default configuration.
>
> When the GRO bit is set, the per-queue NAPI instances are initialized
> and registered. On xmit, when napi instances are available, we try
> to use them.

Am I mistaken in thinking that this also makes XDP redirect into a veth
work without having to load an XDP program on the peer device? That's
been a long-outstanding thing we've been meaning to fix, so that would
be awesome! :)

-Toke