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SubjectRe: [PATCH net-next] tuntap: XDP_TX can use native XDP
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 <jasowang@redhat.com>

Acked-by: Michael S. Tsirkin <mst@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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