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

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Date:   Wed, 15 Nov 2017 18:55:59 -0800
From:   Alexei Starovoitov <ast@...com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        John Fastabend <john.fastabend@...il.com>
CC:     Björn Töpel <bjorn.topel@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.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>
Subject: Re: [RFC PATCH 00/14] Introducing AF_PACKET V4 support

On 11/14/17 4:20 AM, Willem de Bruijn wrote:
>>>>>
>>>>> * Limit the scope of the first patchset to Rx only, and introduce Tx
>>>>>   in a separate patchset.
>>>>
>>>>
>>>> all sounds good to me except above bit.
>>>> I don't remember people suggesting to split it this way.
>>>> What's the value of it without tx?
>>>>
>>>
>>> We definitely need Tx for our use-cases! I'll rephrase, so the
>>> idea was making the initial patch set without Tx *driver*
>>> specific code, e.g. use ndo_xdp_xmit/flush at a later point.
>>>
>>> So AF_ZEROCOPY, the socket parts, would have Tx support.
>>>
>>> @John Did I recall that correctly?
>>>
>>
>> Yep, that is what I said. However, on second thought, without the
>> driver tx half I guess tx will be significantly slower.
>
> The idea was that existing packet rings already send without
> copying, so the benefit from device driver changes is not obvious.
>
> I would leave them out for now and evaluate before possibly
> sending a separate patchset.

are you suggesting to use new af_zerocopy for rx and old
af_packet for tx ? imo that's too cumbersome to use.
New interface has to be symmetrical from the start.