Subject: Re: [RFC PATCH net-next V2 6/6] virtio-net: support XDP rx handler

From: Jesper Dangaard Brouer <[email-masked]>
Date: Tue, 14 Aug 2018 11:22:22 +0200

On Mon, 13 Aug 2018 11:17:30 +0800
Jason Wang <[email-masked]> wrote:

> This patch tries to add the support of XDP rx handler to
> virtio-net. This is straight-forward, just call xdp_do_pass() and
> behave depends on its return value.
> 
> Test was done by using XDP_DROP (xdp1) for macvlan on top of
> virtio-net. PPS of SKB mode was ~1.2Mpps while PPS of native XDP mode
> was ~2.2Mpps. About 83% improvement was measured.

I'm not convinced...

Why are you not using XDP_REDIRECT, which is already implemented in
receive_mergeable (which you modify below).

The macvlan driver just need to implement ndo_xdp_xmit(), and then you
can redirect (with XDP prog from physical driver into the guest).  It
should be much faster...

> Notes: for RFC, only mergeable buffer case was implemented.
> 
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/virtio_net.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 62311dd..1e22ad9 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -777,6 +777,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  	rcu_read_lock();
>  	xdp_prog = rcu_dereference(rq->xdp_prog);
>  	if (xdp_prog) {
> +		rx_xdp_handler_result_t ret;
>  		struct xdp_frame *xdpf;
>  		struct page *xdp_page;
>  		struct xdp_buff xdp;
> @@ -825,6 +826,15 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  
>  		switch (act) {
>  		case XDP_PASS:
> +			ret = xdp_do_pass(&xdp);
> +			if (ret == RX_XDP_HANDLER_DROP)
> +				goto drop;
> +			if (ret != RX_XDP_HANDLER_FALLBACK) {
> +				if (unlikely(xdp_page != page))
> +					put_page(page);
> +				rcu_read_unlock();
> +				goto xdp_xmit;
> +			}
>  			/* recalculate offset to account for any header
>  			 * adjustments. Note other cases do not build an
>  			 * skb and avoid using offset
> @@ -881,6 +891,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  		case XDP_ABORTED:
>  			trace_xdp_exception(vi->dev, xdp_prog, act);
>  			/* fall through */
> +drop:
>  		case XDP_DROP:
>  			if (unlikely(xdp_page != page))
>  				__free_pages(xdp_page, 0);

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer