netdev - Re: Question about veth

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Message-ID: <CAM_iQpVXOsPZrAhBN10JYrVjOOK2_q7=gsFbsi_=s5XZLj1S+g@mail.gmail.com>
Date:   Mon, 23 Jan 2017 12:56:05 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Xiangning Yu <yuxiangning@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Question about veth_xmit()

On Mon, Jan 23, 2017 at 10:46 AM, Xiangning Yu <yuxiangning@...il.com> 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?

For me it is more like for the completeness of network stack of each
netns. The /proc net.core.netdev_max_backlog etc. are per netns, which
means each netns, as an independent network stack, should respect it
too.

Since you care about latency, why not tune net.core.dev_weight for your
own netns?