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

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Date:   Thu, 15 Aug 2019 19:11:11 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     "Samudrala\, Sridhar" <sridhar.samudrala@...el.com>,
        magnus.karlsson@...el.com, bjorn.topel@...el.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        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

"Samudrala, Sridhar" <sridhar.samudrala@...el.com> writes:

> On 8/15/2019 4:12 AM, Toke Høiland-Jørgensen wrote:
>> 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?
>
> The no-skip-bpf results are pretty close to what i see before the 
> patches are applied. As umem is cached in rx_ring for zerocopy the 
> overhead is much smaller compared to the copy scenario where i am 
> currently calling xdp_get_umem_from_qid().

I meant more for other XDP programs; what is the performance impact of
XDP_DROP, for instance?

>> 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...
>
> Yes. This is mainly targeted for application that create 1 AF_XDP
> socket per RX queue and can use a HW filter (via ethtool or TC flower)
> to redirect the packets to a queue or a group of queues.

Yeah, and I'd prefer it if the handling of this to be unified somehow...

-Toke