netdev - Re: [PATCH v15 ] net/veth/XDP: Line-rate packet forwarding in kernel

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Date:   Tue, 3 Apr 2018 19:16:58 -0600
From:   David Ahern <dsahern@...il.com>
To:     "Md. Islam" <mislam4@...t.edu>, netdev@...r.kernel.org,
        David Miller <davem@...emloft.net>, stephen@...workplumber.org,
        agaceph@...il.com, Pavel Emelyanov <xemul@...nvz.org>,
        Eric Dumazet <edumazet@...gle.com>,
        alexei.starovoitov@...il.com, brouer@...hat.com
Subject: Re: [PATCH v15 ] net/veth/XDP: Line-rate packet forwarding in kernel

On 4/1/18 6:47 PM, Md. Islam wrote:
> This patch implements IPv4 forwarding on xdp_buff. I added a new
> config option XDP_ROUTER. Kernel would forward packets through fast
> path when this option is enabled. But it would require driver support.
> Currently it only works with veth. Here I have modified veth such that
> it outputs xdp_buff. I created a testbed in Mininet. The Mininet
> script (topology.py) is attached. Here the topology is:
> 
> h1 -----r1-----h2 (r1 acts as a router)
> 
> This patch improves the throughput from 53.8Gb/s to 60Gb/s on my
> machine. Median RTT also improved from around .055 ms to around .035
> ms.
> 
> Then I disabled hyperthreading and cpu frequency scaling in order to
> utilize CPU cache (DPDK also utilizes CPU cache to improve
> forwarding). This further improves per-packet forwarding latency from
> around 400ns to 200 ns. More specifically, header parsing and fib
> lookup only takes around 82 ns. This shows that this could be used to
> implement linerate packet forwarding in kernel.
> 
> The patch has been generated on 4.15.0+. Please let me know your
> feedback and suggestions. Please feel free to let me know if this
> approach make sense.

This patch is not really using eBPF and XDP but rather trying to
shortcircuit forwarding through a veth pair.

Have you looked at the loss in performance with this config enabled if
there is no r1? i.e., h1 {veth1}  <---> {veth2} / h2. You are adding a
lookup per-packet to the Tx path.

Have you looked at what I would consider a more interesting use case of
packets into a node and delivered to a namespace via veth?

   +--------------------------+---------------
   | Host                     | container
   |                          |
   |        +-------{ veth1 }-|-{veth2}----
   |       |                  |
   +----{ eth1 }------------------

Can xdp / bpf on eth1 be used to speed up delivery to the container?