netdev - Question about veth

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Message-ID: <CAOwmpL3vg56ZqHaYVBy+9dJJ1=GCbgy-m8NY0JrNCV-Z42R_eg@mail.gmail.com>
Date:   Mon, 23 Jan 2017 10:46:17 -0800
From:   Xiangning Yu <yuxiangning@...il.com>
To:     netdev@...r.kernel.org
Subject: Question about veth_xmit()

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.

Thanks,

- Xiangning