netdev - Re: [RFC PATCH 00/14] Introducing AF

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Date:   Thu, 16 Nov 2017 09:26:15 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Alexei Starovoitov <ast@...com>,
        John Fastabend <john.fastabend@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        michael.lundkvist@...csson.com, ravineet.singh@...csson.com,
        Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>,
        Tushar Dave <tushar.n.dave@...cle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        "Rosen, Rami" <rami.rosen@...el.com>,
        "Shaw, Jeffrey B" <jeffrey.b.shaw@...el.com>,
        "Yigit, Ferruh" <ferruh.yigit@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>,
        David Miller <davem@...emloft.net>, brouer@...hat.com,
        Andy Gospodarek <andy@...yhouse.net>,
        Michael Chan <michael.chan@...adcom.com>
Subject: Re: [RFC PATCH 00/14] Introducing AF_PACKET V4 support


On Thu, 16 Nov 2017 08:09:04 +0100 Björn Töpel <bjorn.topel@...il.com> wrote:

> Ideally, it would be best not having to introduce yet another xmit
> ndo. I believe ndo_xdp_xmit/ndo_xdp_flush would be the best fit, but
> we need to extend it with a destructor callback and potentially some
> kind of DMA trait. Why DMA? For zerocopy, we know the working set of
> packet buffers, so they are DMA mapped up front, whereas ndo_xdp_xmit
> does yet another DMA mapping. Paying for the DMA mapping in the
> fast-path is something we'd like to avoid.

I like your idea of reusing ndo_xdp_xmit/ndo_xdp_flush.  At NetConf I
think we agreed that the ndo_xdp_xmit API likely need to change. See[1]
slide 11.  Andy Gospodarek and Michael Chan wanted to look into the
needed API changes (Cc'ed) thus, lets keep them in the loop.

I also appreciate that you are thinking about avoiding the DMA-mapping
at TX.  It would be a welcomed optimization.

[1] http://people.netfilter.org/hawk/presentations/NetConf2017_Seoul/XDP_devel_update_NetConf2017_Seoul.pdf
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer