[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/include/linux/net.h b/include/linux/net.h
index d6a41e6577f6..28195a2d8ff0 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -107,7 +107,7 @@ enum sock_type {
 struct socket {
         socket_state            state;
         unsigned long           flags;
-        struct proto_ops        *ops;
+        const struct proto_ops  *ops;
         struct fasync_struct    *fasync_list;
         struct file             *file;
         struct sock             *sk;
@@ -260,7 +260,7 @@ SOCKCALL_WRAP(name, recvmsg, (struct kiocb *iocb, struct socket *sock, struct ms
 SOCKCALL_WRAP(name, mmap, (struct file *file, struct socket *sock, struct vm_area_struct *vma), \
               (file, sock, vma)) \
               \
-static struct proto_ops name##_ops = {                  \
+static const struct proto_ops name##_ops = {                    \
         .family         = fam,                          \
         .owner          = THIS_MODULE,                  \
         .release        = __lock_##name##_release,      \