Route lookup in ip_finish_output2

Route lookup in ip_finish_output2

[Prashant Batra]

Hi Folks,

I am trying to do a small hack into the kernel just for some 
experimentation wherein I need to do a ipv4 route lookup from 
ip_finish_output2, after the packet is received from outside and has got 
forwarded.

The route lookup is done using kernel API "ip_route_output_flow" with 
the flow having the dst address.
This seems to be working fine with only exception that at very high 
loads, I see certain CPU hikes and the profiling results show that the 
same API comes out to be the culprit.

What I understand is that even to take the forwarding decision the 
kernel ip_rcv should have done the route lookup to decide that the 
packet needs to be forwarded, then why am I seeing a CPU hike in my case.

The second route lookup is done as the original packet has got 
encapsulated within a new IP header having a different destination than 
the original packet.


Thanks,
Prashant
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