netdev - Re: [PATCH net-next] sfc: fix XDP-redirect in this driver

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Message-ID: <CAOJe8K2BC2ABk9SdUm5236iPk=f4BNMsHQxFPsQy+Wc8+QjTSg@mail.gmail.com>
Date:   Mon, 16 Mar 2020 13:45:23 +0300
From:   Denis Kirjanov <kda@...ux-powerpc.org>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Edward Cree <ecree@...arflare.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-net-drivers@...arflare.com, mhabets@...arflare.com,
        cmclachlan@...arflare.com, ilias.apalodimas@...aro.org,
        lorenzo@...nel.org, sameehj@...zon.com
Subject: Re: [PATCH net-next] sfc: fix XDP-redirect in this driver

On 3/16/20, Jesper Dangaard Brouer <brouer@...hat.com> wrote:
> On Mon, 16 Mar 2020 10:10:01 +0000
> Edward Cree <ecree@...arflare.com> wrote:
>
>> On 16/03/2020 08:49, David Miller wrote:
>> > Solarflare folks, please review.
>>
>> This looks like a correct implementation of what it purports to do, so
>> Acked-by: Edward Cree <ecree@...arflare.com>
>
> Thanks for the review!
>
>> It did take me some digging to understand _why_ it was needed though;
>>  Jesper, is there any documentation of the tailroom requirement?  It
>>  doesn't seem to be mentioned anywhere I could find.
>
> I admit that is is poorly documented.  It is a requirement as both
> cpumap and veth have a dependency when they process the redirected
> packet.  We/I also need to update the doc on one page per packet
> requirement, as it is (in-practice) no longer true.

Hi Jesper,

that means that's on-going work to add multi-buffer/page support to XDP, right?

Thanks!
>
> I'm noticing these bugs, because I'm working on a patchset that add
> tailroom extend, and also reserves this 'skb_shared_info' tailroom area.
> The real goal is to later add XDP multi-buffer support, using this
> 'skb_shared_info' tailroom area, as desc here[2]
>
> [2]
> https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp-multi-buffer01-design.org
>
>> (Is there even any up-to-date doc of the XDP driver interface?  The
>>  one at [1] looks a bit stale...)
>> -Ed
>>
>> [1]:
>> https://prototype-kernel.readthedocs.io/en/latest/networking/XDP/design/requirements.html
>
> This is my old and out-dated documentation. I didn't know people were
> still referring to this.  I does score quite high on Google, so I
> guess, that I really need to update this documentation.  (It was my
> plan that this would be merged into kernel tree, but I can see it have
> been bit-rotting for too long).
>
> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer
>
>