[NET]: move struct proto_ops to const

I noticed that some of 'struct proto_ops' used in the kernel may share
a cache line used by locks or other heavily modified data. (default
linker alignement is 32 bytes, and L1_CACHE_LINE is 64 or 128 at
least)

This patch makes sure a 'struct proto_ops' can be declared as const,
so that all cpus can share all parts of it without false sharing.

This is not mandatory : a driver can still use a read/write structure
if it needs to (and eventually a __read_mostly)

I made a global stubstitute to change all existing occurences to make
them const.

This should reduce the possibility of false sharing on SMP, and
speedup some socket system calls.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 96020d7087e8..7849cac14d3a 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -293,7 +293,7 @@ static inline int nl_pid_hash_dilute(struct nl_pid_hash *hash, int len)
         return 0;
 }
 
-static struct proto_ops netlink_ops;
+static const struct proto_ops netlink_ops;
 
 static int netlink_insert(struct sock *sk, u32 pid)
 {
@@ -1656,7 +1656,7 @@ int netlink_unregister_notifier(struct notifier_block *nb)
         return notifier_chain_unregister(&netlink_chain, nb);
 }
                 
-static struct proto_ops netlink_ops = {
+static const struct proto_ops netlink_ops = {
         .family =       PF_NETLINK,
         .owner =        THIS_MODULE,
         .release =      netlink_release,