Libpcap performance problem

[Giray Simsek <giray_simsek () hotmail com>]

Hi,
We are currently working on testing Linux network performance. We have two Linux machines in our test setup. Machine1 
is the attacker machine from which we are sending SYN packets to Machine2 at a rate of 3million pps. We are able to 
receive these packets on Machine2's external interface and forward them through the internal interface without dropping 
any packets. So far no problems. However, when we start another app that captures traffic on Machine2's external 
interface using libpcap, the amount of traffic that is forwarded drops significantly. Obviously, this second libpcap 
app becomes a bottleneck. It can capture only about 800Kpps of traffic and only about 800Kpps can be forwarded in this 
case. This drop in the amount of forwarded traffic is not acceptable for us.
Is there any way we can overcome this problem? Are there any settings on Os, ixgbe driver or libpcap that will allow us 
to forward all the traffic?
Both machines are running Linux kernel 3.15.
Thanks in advance.
Giray                                     
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