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>

1 files changed, 16 insertions, 0 deletions

diff --git a/extensions/libxt_cpu.man b/extensions/libxt_cpu.man
new file mode 100644
index 00000000..f42ac7a5
--- /dev/null
+++ b/extensions/libxt_cpu.man
@@ -0,0 +1,16 @@
+.TP
+[\fB!\fP] \fB\-\-cpu\fP \fInumber\fP
+
+Match cpu handling this packet. cpus are numbered from 0 to NR_CPUS-1
+Can be used in combination with RPS (Remote Packet Steering) or
+multiqueue NICS to spread network traffic on different queues.
+.PP
+Example:
+.PP
+iptables \-t nat \-A PREROUTING \-p tcp \-\-dport 80 \-m cpu \-\-cpu 0 
+        \-j REDIRECT \-\-to\-port 8080
+.PP
+iptables \-t nat \-A PREROUTING \-p tcp \-\-dport 80 \-m cpu \-\-cpu 1 
+        \-j REDIRECT \-\-to\-port 8081
+.PP
+Available since linux 2.6.36