netdev - Re: [flamebait] xdp, well meaning but pointless

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Date:   Sat, 3 Dec 2016 11:19:11 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Florian Westphal <fw@...len.de>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [flamebait] xdp, well meaning but pointless

On Fri, Dec 2, 2016 at 12:22 PM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
>
> On Thu, 1 Dec 2016 10:11:08 +0100 Florian Westphal <fw@...len.de> wrote:
>
>> In light of DPDKs existence it make a lot more sense to me to provide
>> a). a faster mmap based interface (possibly AF_PACKET based) that allows
>> to map nic directly into userspace, detaching tx/rx queue from kernel.
>>
>> John Fastabend sent something like this last year as a proof of
>> concept, iirc it was rejected because register space got exposed directly
>> to userspace.  I think we should re-consider merging netmap
>> (or something conceptually close to its design).
>
> I'm actually working in this direction, of zero-copy RX mapping packets
> into userspace.  This work is mostly related to page_pool, and I only
> plan to use XDP as a filter for selecting packets going to userspace,
> as this choice need to be taken very early.
>
> My design is here:
>  https://prototype-kernel.readthedocs.io/en/latest/vm/page_pool/design/memory_model_nic.html
>
> This is mostly about changing the memory model in the drivers, to allow
> for safely mapping pages to userspace.  (An efficient queue mechanism is
> not covered).

Virtio virtqueues are used in various other locations in the stack.
With separate memory pools and send + completion descriptor rings,
signal moderation, careful avoidance of cacheline bouncing, etc. these
seem like a good opportunity for a TPACKET_V4 format.