netfilter: use jump_label for nf_hooks

On configs where CONFIG_JUMP_LABEL=y, we can replace in fast path a
load/compare/conditional jump by a single jump with no dcache reference.

Jump target is modified as soon as nf_hooks[pf][hook] switches from
empty state to non empty states. jump_label state is kept outside of
nf_hooks array so has no cost on cpu caches.

This patch removes the test on CONFIG_NETFILTER_DEBUG : No need to call
nf_hook_slow() at all if nf_hooks[pf][hook] is empty, this didnt give
useful information, but slowed down things a lot.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 1 deletions

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index afca6c78948c..4aa0f4b19bd8 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -54,6 +54,12 @@ EXPORT_SYMBOL_GPL(nf_unregister_afinfo);
 
 struct list_head nf_hooks[NFPROTO_NUMPROTO][NF_MAX_HOOKS] __read_mostly;
 EXPORT_SYMBOL(nf_hooks);
+
+#if defined(CONFIG_JUMP_LABEL)
+struct jump_label_key nf_hooks_needed[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
+EXPORT_SYMBOL(nf_hooks_needed);
+#endif
+
 static DEFINE_MUTEX(nf_hook_mutex);
 
 int nf_register_hook(struct nf_hook_ops *reg)
@@ -70,6 +76,9 @@ int nf_register_hook(struct nf_hook_ops *reg)
         }
         list_add_rcu(&reg->list, elem->list.prev);
         mutex_unlock(&nf_hook_mutex);
+#if defined(CONFIG_JUMP_LABEL)
+        jump_label_inc(&nf_hooks_needed[reg->pf][reg->hooknum]);
+#endif
         return 0;
 }
 EXPORT_SYMBOL(nf_register_hook);
@@ -79,7 +88,9 @@ void nf_unregister_hook(struct nf_hook_ops *reg)
         mutex_lock(&nf_hook_mutex);
         list_del_rcu(&reg->list);
         mutex_unlock(&nf_hook_mutex);
-
+#if defined(CONFIG_JUMP_LABEL)
+        jump_label_dec(&nf_hooks_needed[reg->pf][reg->hooknum]);
+#endif
         synchronize_net();
 }
 EXPORT_SYMBOL(nf_unregister_hook);