Subject: Re: [bpf-next v3 8/9] bpf: Provide helper to do forwarding lookups in kernel FIB table

From: Jesper Dangaard Brouer <[email-masked]>
Date: Thu, 10 May 2018 09:31:58 +0200

On Wed,  9 May 2018 20:34:26 -0700
David Ahern <[email-masked]> wrote:

> Provide a helper for doing a FIB and neighbor lookup in the kernel
> tables from an XDP program. The helper provides a fastpath for forwarding
> packets. If the packet is a local delivery or for any reason is not a
> simple lookup and forward, the packet continues up the stack.
> 
> If it is to be forwarded, the forwarding can be done directly if the
> neighbor is already known. If the neighbor does not exist, the first
> few packets go up the stack for neighbor resolution. Once resolved, the
> xdp program provides the fast path.
> 
> On successful lookup the nexthop dmac, current device smac and egress
> device index are returned.
> 
> The API supports IPv4, IPv6 and MPLS protocols, but only IPv4 and IPv6
> are implemented in this patch. The API includes layer 4 parameters if
> the XDP program chooses to do deep packet inspection to allow compare
> against ACLs implemented as FIB rules.
> 
> Header rewrite is left to the XDP program.
> 
> The lookup takes 2 flags:
> - BPF_FIB_LOOKUP_DIRECT to do a lookup that bypasses FIB rules and goes
>   straight to the table associated with the device (expert setting for
>   those looking to maximize throughput)
> 
> - BPF_FIB_LOOKUP_OUTPUT to do a lookup from the egress perspective.
>   Default is an ingress lookup.
> 
> Initial performance numbers collected by Jesper, forwarded packets/sec:
> 
>        Full stack    XDP FIB lookup    XDP Direct lookup
> IPv4   1,947,969       7,074,156          7,415,333
> IPv6   1,728,000       6,165,504          7,262,720
> 

The "Full stack" tests were with netfilter modules unloaded.  Default
setting with netfilter conntrack loaded and default Fedora firewall
rules, show around 700Kpps.

> These number are single CPU core forwarding on a Broadwell
> E5-1650 v4 @ 3.60GHz.
> 
> Signed-off-by: David Ahern <[email-masked]>

Acked-by: Jesper Dangaard Brouer <[email-masked]>

This helper is awesome, as it really shows how XDP is meant to work in
concert and cooperate with the existing network stack.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer