perfsonar development work

[ulisses <>]

Hi all

yesterday Sven at JRA1 meeting said that he obtained ~300 Mbps with 
a regular NIC.

~3 years ago I obtained similar results ~240 Mbps (without any packet loss)
with conventional and a Pentium-III @800 Mhz.

To obtain similar performance as Sven with much older hardware the key
differenc is to use PACKET_MMAP:

  - Without PACKET_MMAP enabled libpcap has to issue two system calls for 
each packet,
    one for receiving the packet and another for getting the timestamp.

  - With a PACKET_MMAP enabled libpcap, usually no systems calls are issued 
at all,
    packets are already mapped at process memory.

PACKET_MMAP is a kernel feature, and requires to be enabled in the kernel 
(usually is)
but also requires a PACKET_MMAP enabled libpcap, I have never seen a Linux 
distro
that provided support for it!

For the applications, it's a matter of replacing one libpcap by another one
that supports PACKET_MMAP.

For more information on it you can read: 

        http://pusa.uv.es/~ulisses/packet_mmap/packet_mmap.txt

in that document, there are links to libpcap versions that support
PACKET_MMAP, try the one from the .gov site.

I hope this helps

        Ulisses
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