Re: Question about veth_xmit()

On Mon, Jan 23, 2017 at 12:56 PM, Cong Wang [off-list ref] wrote:

On Mon, Jan 23, 2017 at 10:46 AM, Xiangning Yu [off-list ref] wrote:

quoted

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