Re: best strategy for receiving millions-packets-per-second

["Montorsi, Francesco via tcpdump-workers" <tcpdump-workers () lists tcpdump org>]

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> From: "Montorsi, Francesco" <fmontorsi () empirix com>
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> Date: Mon, 4 May 2020 13:00:45 +0000
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> Hi Ray,
>
> > On 04/05/2020 11:08, Montorsi, Francesco wrote:
> > > a) what's the best way to load-balance received packets across a pool of threads / CPU cores: libpcap API is 
> > > single-thread right?
> >
> > Assuming Linux (since you mentioned DPDK) 
> yes, right  - I forgot to mention that.
>
> > you can get per-packet
> > load-balancing by forgetting libpcap and going straight for `AF_PACKET`
> > and then use the ioctl `PACKET_FANOUT_CPU` to keep packets on whichever
> > CPU core handles that RX queue.
>
> Thanks for pointing this out, that was my same suspect.
>
>
> > You need sufficient entropy on the incoming packets IP and port fields
> > for the RSS algortihm to ensure effective per-queue balancing on the
> > traffic.
> > See slide 11 onwards from my presentation here:
> > <https://indico.dns-oarc.net/event/31/contributions/691/attachments/656/1078/Local_Root.pdf>
>
> Thanks I had a look.
> My problem is that very often my application will receive packets encapsulated through GRE/ERSPAN or GTPU tunnelling 
> protocols
> so that the outer IP addresses that Linux will use for hashing and dispatching across queues risk to be always the same.
> That would mean close-to-zero entropy and all packets dispatched to the same CPU core.
> I guess I would use PACKET_FANOUT_LB to distribute traffic on a set of intermediate CPUs that would compute the hash 
> using the 
> tunnelled IP addresses instead of the "outer" ones and then redistribute packets over the actual worker threads...
>
> Do you know if there is any plan to get AF_PACKET support in libpcap anytime soon?
>
> Thanks,
> Francesco
>
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