Re: [PATCH nf-next 2/5] netfilter: flowtable: consolidate xmit path

[Florian Westphal <fw@strlen.de>]

Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> Use dev_queue_xmit() for the XMIT_NEIGH case. Store the interface index
> of the real device behind the vlan/pppoe device, this introduces  an
> extra lookup for the real device in the xmit path because rt->dst.dev
> provides the vlan/pppoe device.

Will this scale?  netdev_by_index only has a fixed table of 256 slots,
so with 8k vlans or so this will have a 30-ish netdev list walk.

[ EDIT: I see now that nf_flow_queue_xmit() already does that.
  So I guess its either not an issue or not yet and it can be
  optimized later.  So disregard this ]

>  	case FLOW_OFFLOAD_XMIT_NEIGH:
>  		rt = dst_rtable(tuplehash->tuple.dst_cache);
> -		outdev = rt->dst.dev;
> -		skb->dev = outdev;
> -		nexthop = rt_nexthop(rt, flow->tuplehash[!dir].tuple.src_v4.s_addr);
> +		xmit.outdev = dev_get_by_index_rcu(state->net, tuplehash->tuple.ifidx);

Why do this if we already have dst_cache?

The above explanation (rt->dst.dev could be a tunnel device, whereas
the latter fetches phyical / lowest device) from the commit message
makes that clear; but I think a short comment would help.