Packet drop while using BPF filter

[mukesh.fkd@gmail.com (Mukesh Yadav)]

Hi Guys,

I am working on user level code which uses BPF filter.
Solution has two threads and  BPF filter for incoming packets to raw socket
dedicated to each thread.
Intent is to divide ingress traffic between two thread based on whether
dest IP is even or odd.

BPF filters used are:
Even IP filter :-> tcpdump -i interface 'ether dst <dest mac> && ip[19] &
0x01 = 0'
Odd IP filter :->  tcpdump -i interface  'ether dst <dest mac> && ip[19] &
0x01 = 1'

There is a packet loss for odd IP thread even when CPU is available. Reason
being packet drop due  recv buffer full.
Same amount of traffic is well handled by even IP thread(user code being
same in both), scaling CPU to full 100%.

In odd IP thread, If filter is changed to "tcpdump -i interface  'ether dst
<dest mac> && ip proto 17' ", all goes fine.
Also CPU usage at kernel drops from 50% to 4 % for a particular amount of
traffic.

Would appreciate any I/ps for reducing load at kernel for packet
filtering(Odd/Even IP distribution)


Cheers
Mukesh
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