netfilter: add 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 is 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, 63 insertions, 0 deletions

diff --git a/net/netfilter/xt_cpu.c b/net/netfilter/xt_cpu.c
new file mode 100644
index 000000000000..b39db8a5cbae
--- /dev/null
+++ b/net/netfilter/xt_cpu.c
@@ -0,0 +1,63 @@
+/* Kernel module to match running CPU */
+
+/*
+ * Might be used to distribute connections on several daemons, if
+ * RPS (Remote Packet Steering) is enabled or NIC is multiqueue capable,
+ * each RX queue IRQ affined to one CPU (1:1 mapping)
+ *
+ */
+
+/* (C) 2010 Eric Dumazet
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/netfilter/xt_cpu.h>
+#include <linux/netfilter/x_tables.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Eric Dumazet <eric.dumazet@gmail.com>");
+MODULE_DESCRIPTION("Xtables: CPU match");
+
+static int cpu_mt_check(const struct xt_mtchk_param *par)
+{
+	const struct xt_cpu_info *info = par->matchinfo;
+
+	if (info->invert & ~1)
+		return -EINVAL;
+	return 0;
+}
+
+static bool cpu_mt(const struct sk_buff *skb, struct xt_action_param *par)
+{
+	const struct xt_cpu_info *info = par->matchinfo;
+
+	return (info->cpu == smp_processor_id()) ^ info->invert;
+}
+
+static struct xt_match cpu_mt_reg __read_mostly = {
+	.name       = "cpu",
+	.revision   = 0,
+	.family     = NFPROTO_UNSPEC,
+	.checkentry = cpu_mt_check,
+	.match      = cpu_mt,
+	.matchsize  = sizeof(struct xt_cpu_info),
+	.me         = THIS_MODULE,
+};
+
+static int __init cpu_mt_init(void)
+{
+	return xt_register_match(&cpu_mt_reg);
+}
+
+static void __exit cpu_mt_exit(void)
+{
+	xt_unregister_match(&cpu_mt_reg);
+}
+
+module_init(cpu_mt_init);
+module_exit(cpu_mt_exit);