tree 37672b09c51845f5255185767f0624bf9c09d559
parent 59ccf53b9414d998afd6169cb2d6ba0f3c249081
author Eric Dumazet <eric.dumazet@gmail.com> 1279894514 +0200
committer Patrick McHardy <kaber@trash.net> 1279894514 +0200

extension: add xt_cpu match

Kernel 2.6.36 supports xt_cpu match

In some situations a CPU match permits a better spreading of
connections, or select targets only for a given cpu.

With Remote Packet Steering or multiqueue NIC and appropriate IRQ
affinities, we can distribute trafic on available cpus, per session.
(all RX packets for a given flow are handled by a given cpu)

Some legacy applications being not SMP friendly, one way to scale a
server is to run multiple copies of them.

Instead of randomly choosing an instance, we can use the cpu number as a
key so that softirq handler for a whole instance is running on a single
cpu, maximizing cache effects in TCP/UDP stacks.

Using NAT for example, a four ways machine might run four copies of
server application, using a separate listening port for each instance,
but still presenting an unique external port :

iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 0 \
        -j REDIRECT --to-port 8080

iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 \
        -j REDIRECT --to-port 8081

iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 2 \
        -j REDIRECT --to-port 8082

iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 3 \
        -j REDIRECT --to-port 8083

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>