Hi Giray copying packets from kernel space to user space is costly, that’s why you see this performance drop, packet forwarding is also affected because you are adding overhead. Can I ask you why you cannot bypass the kernel?
Alfredo > On 29 Jan 2015, at 09:48, Giray Simsek <[email protected]> wrote: > > Hi, > > I'm currently working on testing Linux network performance. I 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. I'm 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 I 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. Since I hit this bottleneck I > performed the same test using pf_ring aware libpcap using pfcount. The amount > of traffic that we captured was better now (~ 1.2 Mpps) but still the > forwarded traffic was limited by the capturing application. Only about ~1.2 > Mpps is forwarded. Roughly the same amount as captured. I used > transparent_mode=1. I don't use DNA since I don't want to bypass kernel. > > What I don't understand is why is the capturing performance limiting the > forwarding performance? If I set a filter on libpcap and capture just a small > amount (say 100Kpps) of the incoming traffic, then the forwarding performance > is not affected? Any ideas to overcome this problem? Are there any pf_ring > related solutions? > > Both machines are running Linux kernel 3.15. > > Thanks in advance. > Giray > _______________________________________________ > Ntop-misc mailing list > [email protected] <mailto:[email protected]> > http://listgateway.unipi.it/mailman/listinfo/ntop-misc > <http://listgateway.unipi.it/mailman/listinfo/ntop-misc>
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