netdev - Re: [net PATCH 1/4] virtio_net: disable XDP_REDIRECT in receive

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Date:   Tue, 27 Feb 2018 10:25:30 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     netdev@...r.kernel.org, John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [net PATCH 1/4] virtio_net: disable XDP_REDIRECT in
 receive_mergeable() case



On 2018年02月27日 08:40, Michael S. Tsirkin wrote:
>> IMHO we should consider NOT supporting XDP in receive_mergeable() at
>> all, because the principles behind XDP are to gain speed by (1) code
>> simplicity, (2) sacrificing memory and (3) where possible moving
>> runtime checks to setup time.  These principles are clearly being
>> violated in receive_mergeable(), that e.g. runtime track average
>> buffer size to save memory consumption.
>>
>> In the longer run, we should consider introducing a separate receive
>> function when attaching an XDP program, and also change the memory
>> model to be compatible with XDP when attaching an XDP prog.
> I agree with a separate function approach.
>
> So each buffer is tagged as xdp/non xdp, we check that
> and handle appropriately - where non xdp could be handled
> by the generic path.

If we want to have separated function, should we do it for all XDP 
capable drivers instead of virtio-net only?

Thanks