Re: [PATCH bpf-next 0/5] Add support for SKIP_BPF flag for AF_XDP sockets

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Sridhar Samudrala <sridhar.samudrala@intel.com> writes:

> This patch series introduces XDP_SKIP_BPF flag that can be specified
> during the bind() call of an AF_XDP socket to skip calling the BPF 
> program in the receive path and pass the buffer directly to the socket.
>
> When a single AF_XDP socket is associated with a queue and a HW
> filter is used to redirect the packets and the app is interested in
> receiving all the packets on that queue, we don't need an additional 
> BPF program to do further filtering or lookup/redirect to a socket.
>
> Here are some performance numbers collected on 
>   - 2 socket 28 core Intel(R) Xeon(R) Platinum 8180 CPU @ 2.50GHz
>   - Intel 40Gb Ethernet NIC (i40e)
>
> All tests use 2 cores and the results are in Mpps.
>
> turbo on (default)
> ---------------------------------------------	
>                       no-skip-bpf    skip-bpf
> ---------------------------------------------	
> rxdrop zerocopy           21.9         38.5 
> l2fwd  zerocopy           17.0         20.5
> rxdrop copy               11.1         13.3
> l2fwd  copy                1.9          2.0
>
> no turbo :  echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo
> ---------------------------------------------	
>                       no-skip-bpf    skip-bpf
> ---------------------------------------------	
> rxdrop zerocopy           15.4         29.0
> l2fwd  zerocopy           11.8         18.2
> rxdrop copy                8.2         10.5
> l2fwd  copy                1.7          1.7
> ---------------------------------------------

You're getting this performance boost by adding more code in the fast
path for every XDP program; so what's the performance impact of that for
cases where we do run an eBPF program?

Also, this is basically a special-casing of a particular deployment
scenario. Without a way to control RX queue assignment and traffic
steering, you're basically hard-coding a particular app's takeover of
the network interface; I'm not sure that is such a good idea...

-Toke