Performance impact with multiple pcap handlers on Linux

[Linus Lüssing via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

> --- Begin Message ---
>
>
> From: Linus Lüssing <linus.luessing () c0d3 blue>
>
> Date: Tue, 22 Dec 2020 23:05:33 +0100
>
> Hi,
>
> I was experimenting a bit with migrating from the use of
> pcap_offline_filter() to pcap_setfilter().
>
> I was a bit surprised that installing for instance 500 pcap
> handlers with a BPF rule "arp" via pcap_setfilter() reduced
> the TCP performance of iperf3 over veth interfaces from 73.8 Gbits/sec
> to 5.39 Gbits/sec. Using only one or even five handlers seemed
> fine (71.7 Gbits/sec and 70.3 Gbits/sec).
>
> Is that expected?
>
> Full test setup description and more detailed results can be found
> here: https://github.com/lemoer/bpfcountd/pull/8
>
> Regards, Linus
>
> PS: And I was also surprised that there seems to be a limit of
> only 510 pcap handlers on Linux.
>
> --- End Message ---
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