netdev - Re: [PATCH] net-xdp: netdev attribute to control xdpgeneric skb linearization

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Message-ID: <CA+hQ2+g+owSWzwEsnYmnY2S3ipCXPXsghYF0--aorTCJ1gVpSg@mail.gmail.com>
Date:   Wed, 5 Feb 2020 07:36:15 -0800
From:   Luigi Rizzo <rizzo@....unipi.it>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Luigi Rizzo <lrizzo@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        netdev <netdev@...r.kernel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Jubran, Samih" <sameehj@...zon.com>
Subject: Re: [PATCH] net-xdp: netdev attribute to control xdpgeneric skb linearization

On Fri, Jan 24, 2020 at 1:28 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Luigi Rizzo <lrizzo@...gle.com> writes:
>
> > On Fri, Jan 24, 2020 at 7:31 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> >>
> >> Luigi Rizzo <lrizzo@...gle.com> writes:
> >>
> > ...
> >> > My motivation for this change is that enforcing those guarantees has
> >> > significant cost (even for native xdp in the cases I mentioned - mtu >
> >> > 1 page, hw LRO, header split), and this is an interim solution to make
> >> > generic skb usable without too much penalty.
> >>
> >> Sure, that part I understand; I just don't like that this "interim"
> >> solution makes generic and native XDP diverge further in their
> >> semantics...
> >
> > As a matter of fact I think it would make full sense to use the same approach
> > to control whether native xdp should pay the price converting to linear buffers
> > when the hw cannot guarantee that.
> >
> > To me this seems to be a case of "perfect is enemy of good":..
>
> Hmm, I can kinda see your point (now that I've actually grok'ed how the
> length works with skbs and generic XDP :)). I would still worry that
> only having the header there would lead some XDP programs to just
> silently fail. But on the other hand, this is opt-in... so IDK - maybe
> this is fine to merge as-is, and leave improvements for later?

Sorry I let this slip, any consensus on this patch?

Thanks
Luigi

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