Re: [net PATCH 1/4] virtio_net: disable XDP_REDIRECT in receive_mergeable() case

[Jason Wang <jasowang@redhat.com>]

On 2018年02月27日 10:25, Jason Wang wrote:
>
>
> 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
>

What's more, since we don't stop device during XDP set. Even if a buffer 
is tagged as xdp/non xdp during refill, we still can't make sure whether 
or not XDP was used at receive function. So we can not handle them 
separately.

Thanks