Re: libpcap capture performance drop

[Guy Harris <guy () alum mit edu>]

On Aug 15, 2010, at 6:15 AM, Doktor Bernd wrote:

> thanks for the advice. If I use libpcap 1.1.1 compiled with the HAVE_PACKET_RING stuff commented out, the my softare 
> performs very well.
> Ubuntu currently ships with 1.0.0.6 I think. If I use that version my application has problems capturing 100 Mbit/s 
> of traffic. If I change to the custom build version of libpcap then I can capture 1 Gbit/s of traffic and problem 
> occur only for small packet sizes (<100 Byte).

What happens if you build 1.1.1 with no changes (i.e., with the HAVE_PACKET_RING stuff *not* commented out) and use 
that version?  That's the cleanest test of mmap vs. non-mmap.

> Any idea why mmap is slowing everything down? I am using pcap_dispatch to capture packet by packet.

(That means you're not using pcap_next() or pcap_next_ex(), correct?)

What are you passing as the second argument to pcap_dispatch()?

And how are you measuring the packet loss?  Are you using the figures from pcap_stats(), or are you determining in some 
other fashion that packets weren't captured?-
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