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

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Date:   Thu, 15 Aug 2019 23:25:55 -0700
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     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



On 8/15/2019 12:28 PM, Jakub Kicinski wrote:
> On Wed, 14 Aug 2019 20:46:18 -0700, Sridhar Samudrala wrote:
>> 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
>> ---------------------------------------------	
> 
> Could you include a third column here - namely the in-XDP performance?
> AFAIU the way to achieve better performance with AF_XDP is to move the
> fast path into the kernel's XDP program..

The in-xdp drop that can be measured with xdp1 is lower than rxdrop
zerocopy with skip-bpf although in-xdp drop uses only 1 core. af-xdp 
1-core performance would improve with need-wakeup or busypoll patches 
and based on early experiments so far af-xdp with need-wakeup/busypoll + 
skip-bpf perf is higher than in-xdp drop.

Will include in-xdp drop data too in the next revision.

> 
> Maciej's work on batching XDP program's execution should lower the
> retpoline overhead, without leaning close to the bypass model.
>