On Mon, 2017-01-23 at 10:46 -0800, Xiangning Yu wrote:
> Hi netdev folks,
>
> It looks like we call dev_forward_skb() in veth_xmit(), which calls
> netif_rx() eventually.
>
> While netif_rx() will enqueue the skb to the CPU RX backlog before the
> actual processing takes place. So, this actually means a TX skb has to
> wait some un-related RX skbs to finish. And this will happen twice for
> a single ping, because the veth device always works as a pair?
>
> IMHO this might lead to some latency issue under certain workload,
> can we change the call to dev_forward_skb() to something like this?
>
> if (likely(__dev_forward_skb(rcv, skb) == NET_RX_SUCCESS)) {
> local_bh_disable();
> netif_receive_skb(skb);
> local_bh_enable();
>
> Could you please shed some light on this change? And please feel free
> to correct my if my understanding is wrong.
How veth would have different latency requirement than loopback device ?
Calling netif_receive_skb() is considered too dangerous here (or from
any ndo_start_xmit()) because of possible kernel stack exhaustion.
