Re: libpcap capture performance drop

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

On Aug 10, 2010, at 3:35 AM, Doktor Bernd wrote:

> I am experiencing the same problem as described in
> http://news.gmane.org/find-root.php?message_id=%3c972613.6039.qm%40web59701.mail.ac4.yahoo.com%3e
>
> I have written a software that captures Ethernet frames and forwards them to different interfaces.
>
> On Ubuntu 8.10 the software is able to handle 100 Mbit/s without drops on a Intel Core 2 Duo System. When upgrading 
> to any other version of Ubuntu, I experience between 0.5 and 3% packet loss on the same system and also on systems 
> using Intel Core 2 Quad CPUs.
>
> The libpcap version of Ubuntu 8.10 was 0.9.8 and it was upgraded with later Ubuntu versions.
>
> I wanted to try to disable mmap (using libpcap-1.1.1) as suggested in the previous post
>  "for Linux, after running the configure script, get rid of the definition of HAVE_PACKET_RING in config.h;"
>
> But I could not find HAVE_PACKET_RING in the created config.h and also nothing related in the ./configure output.
> Has this been changed?

No.  I forgot that the availability of the memory-mapped pcap mechanism isn't determined by the configure script, it's 
determined by what the system includes offer.

Instead, in pcap-linux.c, just #if 0 out the

 /* check for memory mapped access avaibility. We assume every needed
  * struct is defined if the macro TPACKET_HDRLEN is defined, because it
  * uses many ring related structs and macros */
# ifdef TPACKET_HDRLEN
#  define HAVE_PACKET_RING
#  ifdef TPACKET2_HDRLEN
#   define HAVE_TPACKET2
#  else
#   define TPACKET_V1   0
#  endif /* TPACKET2_HDRLEN */
# endif /* TPACKET_HDRLEN */
#endif /* PF_PACKET */

stuff, so that HAVE_PACKET_RING isn't defined.-
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