On 04/01/2018 05:47 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.
Make sense although lets try to avoid hard coded routing into
XDP xmit routines. See details below.
> +#ifdef CONFIG_XDP_ROUTER
> +int veth_xdp_xmit(struct net_device *dev, struct xdp_buff *xdp)
> +{
This is nice but instead of building a new config_xdp_router
just enable standard XDP for veth + a new helper call to
do routing. Then it will be immediately usable from any XDP
enabled device.
> + struct veth_priv *priv = netdev_priv(dev);
> + struct net_device *rcv;
> + struct ethhdr *ethh;
> + struct sk_buff *skb;
> + int length = xdp->data_end - xdp->data;
> +
> + rcu_read_lock();
> + rcv = rcu_dereference(priv->peer);
> + if (unlikely(!rcv)) {
> + kfree(xdp);
> + goto drop;
> + }
> +
> + /* Update MAC address and checksum */
> + ethh = eth_hdr_xdp(xdp);
> + ether_addr_copy(ethh->h_source, dev->dev_addr);
> + ether_addr_copy(ethh->h_dest, rcv->dev_addr);
> +
> + /* if IP forwarding is enabled on the receiver,
> + * call xdp_router_forward()
> + */
> + if (is_forwarding_enabled(rcv)) {
> + prefetch_xdp(xdp);
> + if (likely(xdp_router_forward(rcv, xdp) == NET_RX_SUCCESS)) {
> + struct pcpu_vstats *stats = this_cpu_ptr(dev->vstats);
> +
> + u64_stats_update_begin(&stats->syncp);
> + stats->bytes += length;
> + stats->packets++;
> + u64_stats_update_end(&stats->syncp);
> + goto success;
> + }
> + }
> +
> + /* Local deliver */
> + skb = (struct sk_buff *)xdp->data_meta;
> + if (likely(dev_forward_skb(rcv, skb) == NET_RX_SUCCESS)) {
> + struct pcpu_vstats *stats = this_cpu_ptr(dev->vstats);
> +
> + u64_stats_update_begin(&stats->syncp);
> + stats->bytes += length;
> + stats->packets++;
> + u64_stats_update_end(&stats->syncp);
> + } else {
> +drop:
> + atomic64_inc(&priv->dropped);
> + }
> +success:
> + rcu_read_unlock();
> + return NETDEV_TX_OK;
> +}
> +#endif
> +
> static const struct net_device_ops veth_netdev_ops = {
> .ndo_init = veth_dev_init,
> .ndo_open = veth_open,
> @@ -290,6 +370,9 @@ static const struct net_device_ops veth_netdev_ops = {
> .ndo_get_iflink = veth_get_iflink,
> .ndo_features_check = passthru_features_check,
> .ndo_set_rx_headroom = veth_set_rx_headroom,
> +#ifdef CONFIG_XDP_ROUTER
> + .ndo_xdp_xmit = veth_xdp_xmit,
> +#endif
> };
>
[...]
> +#ifdef CONFIG_XDP_ROUTER
> +int ip_route_lookup(__be32 daddr, __be32 saddr,
> + u8 tos, struct net_device *dev,
> + struct fib_result *res);
> +#endif
> +
Can the above be a normal BPF helper that returns an
ifindex? Then something roughly like this patter would
work for all drivers with redirect support,
route_ifindex = ip_route_lookup(__daddr, ....)
if (!route_ifindex)
return do_foo()
return xdp_redirect(route_ifindex);
So my suggestion is,
1. enable veth xdp (including redirect support)
2. add a helper to lookup route from routing table
Alternatively you can skip step (2) and encode the routing
table in BPF directly. Maybe we need a more efficient data
structure but that should also work.
Thanks,
John
