netdev - Re: [PATCH net-next 0/2] virtio-net: re enable XDP

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Date:   Thu, 1 Mar 2018 17:23:37 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        john.fastabend@...il.com
Subject: Re: [PATCH net-next 0/2] virtio-net: re enable XDP_REDIRECT for
 mergeable buffer



On 2018年03月01日 17:10, Jesper Dangaard Brouer wrote:
> On Thu,  1 Mar 2018 11:19:03 +0800
> Jason Wang <jasowang@...hat.com> wrote:
>
>> This series tries to re-enable XDP_REDIRECT for mergeable buffer which
>> was removed since commit 7324f5399b06 ("virtio_net: disable
>> XDP_REDIRECT in receive_mergeable() case"). Main concerns are:
>>
>> - not enough tailroom was reserved which breaks cpumap
> To address this at a more fundamental level, I would suggest that we/you
> instead extend XDP to know it's buffers "frame" size/end.  (The
> assumption use to be, xdp_buff->data_hard_start + PAGE_SIZE, but
> ixgbe+virtio_net broke that assumption).
>
> It should actually be fairly easy to implement:
>   * Simply extend xdp_buff with a "data_hard_end" pointer.

Right, and then cpumap can warn and drop packets with insufficient 
tailroom. But it should be a patch on top of this I think.

Thanks

>
> Now cpumap is more safe... instead of crashing, it can now know/see when
> it is safe to create an SKB using build_skb (could fallback to
> dev_alloc_skb).
>