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

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Date:   Thu, 15 Aug 2019 13:12:37 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Sridhar Samudrala <sridhar.samudrala@...el.com>,
        magnus.karlsson@...el.com, bjorn.topel@...el.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        sridhar.samudrala@...el.com, intel-wired-lan@...ts.osuosl.org,
        maciej.fijalkowski@...el.com, tom.herbert@...el.com
Subject: Re: [PATCH bpf-next 0/5] Add support for SKIP_BPF flag for AF_XDP sockets

Sridhar Samudrala <sridhar.samudrala@...el.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