[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>

3 files changed, 5 insertions, 5 deletions

diff --git a/include/net/inet_common.h b/include/net/inet_common.h
index f943306ce5ff..227adcbdfec8 100644
--- a/include/net/inet_common.h
+++ b/include/net/inet_common.h
@@ -1,8 +1,8 @@
 #ifndef _INET_COMMON_H
 #define _INET_COMMON_H
 
-extern struct proto_ops         inet_stream_ops;
-extern struct proto_ops         inet_dgram_ops;
+extern const struct proto_ops           inet_stream_ops;
+extern const struct proto_ops           inet_dgram_ops;
 
 /*
  *      INET4 prototypes used by INET6
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index e3d5d7bc8837..11a725662c36 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -538,8 +538,8 @@ extern int sysctl_ip6frag_low_thresh;
 extern int sysctl_ip6frag_time;
 extern int sysctl_ip6frag_secret_interval;
 
-extern struct proto_ops inet6_stream_ops;
-extern struct proto_ops inet6_dgram_ops;
+extern const struct proto_ops inet6_stream_ops;
+extern const struct proto_ops inet6_dgram_ops;
 
 extern int ip6_mc_source(int add, int omode, struct sock *sk,
                          struct group_source_req *pgsr);
diff --git a/include/net/protocol.h b/include/net/protocol.h
index a29cb29647d0..63f7db99c2a6 100644
--- a/include/net/protocol.h
+++ b/include/net/protocol.h
@@ -65,7 +65,7 @@ struct inet_protosw {
         int              protocol; /* This is the L4 protocol number.  */
 
         struct proto     *prot;
-        struct proto_ops *ops;
+        const struct proto_ops *ops;
   
         int              capability; /* Which (if any) capability do
                                       * we need to use this socket