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

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:

quoted

quoted

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