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

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Date:   Wed, 05 Feb 2020 16:55:45 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Luigi Rizzo <rizzo@....unipi.it>
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

Luigi Rizzo <rizzo@....unipi.it> writes:

> 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?

Dunno if there's a consensus, but I certainly ran out of objections ;)

-Toke