On Wed, Mar 14, 2018 at 11:23:40AM +0800, Jason Wang wrote:
> Now we have ndo_xdp_xmit, switch to use it instead of the slow generic
> XDP TX routine. XDP_TX on TAP gets ~20% improvements from ~1.5Mpps to
> ~1.8Mpps on 2.60GHz Core(TM) i7-5600U.
> 
> Signed-off-by: Jason Wang <jasow...@redhat.com>

Acked-by: Michael S. Tsirkin <m...@redhat.com>

> ---
>  drivers/net/tun.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 475088f..baeafa0 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1613,7 +1613,6 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
> *tun,
>       unsigned int delta = 0;
>       char *buf;
>       size_t copied;
> -     bool xdp_xmit = false;
>       int err, pad = TUN_RX_PAD;
>  
>       rcu_read_lock();
> @@ -1671,8 +1670,14 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
> *tun,
>                       preempt_enable();
>                       return NULL;
>               case XDP_TX:
> -                     xdp_xmit = true;
> -                     /* fall through */
> +                     get_page(alloc_frag->page);
> +                     alloc_frag->offset += buflen;
> +                     if (tun_xdp_xmit(tun->dev, &xdp))
> +                             goto err_redirect;
> +                     tun_xdp_flush(tun->dev);

Why do we have to flush here though?
It might be a good idea to document the reason in a code comment.

> +                     rcu_read_unlock();
> +                     preempt_enable();
> +                     return NULL;
>               case XDP_PASS:
>                       delta = orig_data - xdp.data;
>                       break;
> @@ -1699,14 +1704,6 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
> *tun,
>       get_page(alloc_frag->page);
>       alloc_frag->offset += buflen;
>  
> -     if (xdp_xmit) {
> -             skb->dev = tun->dev;
> -             generic_xdp_tx(skb, xdp_prog);
> -             rcu_read_unlock();
> -             preempt_enable();
> -             return NULL;
> -     }
> -
>       rcu_read_unlock();
>       preempt_enable();
>  
> -- 
> 2.7.4

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