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netfilter: xt_NFQUEUE: introduce CPU fanout
Current NFQUEUE target uses a hash, computed over source and
destination address (and other parameters), for steering the packet
to the actual NFQUEUE. This, however forgets about the fact that the
packet eventually is handled by a particular CPU on user request.
If E. g.
1) IRQ affinity is used to handle packets on a particular CPU already
(both single-queue or multi-queue case)
and/or
2) RPS is used to steer packets to a specific softirq
the target easily chooses an NFQUEUE which is not handled by a process
pinned to the same CPU.
The idea is therefore to use the CPU index for determining the
NFQUEUE handling the packet.
E. g. when having a system with 4 CPUs, 4 MQ queues and 4 NFQUEUEs it
looks like this:
+-----+ +-----+ +-----+ +-----+
|NFQ#0| |NFQ#1| |NFQ#2| |NFQ#3|
+-----+ +-----+ +-----+ +-----+
^ ^ ^ ^
| |NFQUEUE | |
+ + + +
+-----+ +-----+ +-----+ +-----+
|rx-0 | |rx-1 | |rx-2 | |rx-3 |
+-----+ +-----+ +-----+ +-----+
The NFQUEUEs not necessarily have to start with number 0, setups with
less NFQUEUEs than packet-handling CPUs are not a problem as well.
This patch extends the NFQUEUE target to accept a new
NFQ_FLAG_CPU_FANOUT flag. If this is specified the target uses the
CPU index for determining the NFQUEUE being used. I have to introduce
rev3 for this. The 'flags' are folded into _v2 'bypass'.
By changing the way which queue is assigned, I'm able to improve the
performance if the processes reading on the NFQUEUs are pinned
correctly.
Signed-off-by: 
Holger Eitzenberger <holger@eitzenberger.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>