netdev - Re: Question about veth

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Date:   Mon, 23 Jan 2017 13:46:56 -0800
From:   Xiangning Yu <yuxiangning@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Question about veth_xmit()

On Mon, Jan 23, 2017 at 12:56 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> 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?

I haven't tried that yet, thank you for the hint! Though normally one
of the veth device will be in the global namespace.

Thanks,
- Xiangning