On Tue, Feb 23, 2016 at 4:53 AM, Paolo Abeni <pab...@redhat.com> wrote:
> The rx headroom for veth dev is the peer device needed_headroom.
> Avoid ping-pong updates setting the private flag IFF_PHONY_HEADROOM.
>
> This avoids skb head reallocation when forwarding from a veth dev
> towards a device adding some kind of encapsulation.
>
> When forwarding frames below the MTU size towards a vxlan device,
> this gives about 10% performance speed-up when OVS is used to connect
> the veth and the vxlan device and a little more when using a
> plain Linux bridge.
>
> Signed-off-by: Paolo Abeni <pab...@redhat.com>
> ---
> drivers/net/veth.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index ba21d07..4f30a6a 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -35,6 +35,7 @@ struct pcpu_vstats {
> struct veth_priv {
> struct net_device __rcu *peer;
> atomic64_t dropped;
> + unsigned requested_headroom;
> };
>
> /*
> @@ -271,6 +272,29 @@ static int veth_get_iflink(const struct net_device *dev)
> return iflink;
> }
>
> +static void veth_set_rx_headroom(struct net_device *dev, int new_hr)
> +{
> + struct veth_priv *peer_priv, *priv = netdev_priv(dev);
> + struct net_device *peer;
> +
> + if (new_hr < 0)
> + new_hr = 0;
> +
> + rcu_read_lock();
> + peer = rcu_dereference(priv->peer);
> + if (unlikely(!peer))
> + goto out;
> +
> + peer_priv = netdev_priv(peer);
> + priv->requested_headroom = new_hr;
> + new_hr = max(priv->requested_headroom, peer_priv->requested_headroom);
> + dev->needed_headroom = new_hr;
> + peer->needed_headroom = new_hr;
> +
> +out:
> + rcu_read_unlock();
> +}
> +
I am not sure why new priv->requested_headroom is introduced. I think
you can just compare new_hr with dev->needed_headroom and set the max
value to both devices.
