netns: reorder fields in struct net

In a network bench, I noticed an unfortunate false sharing between
'loopback_dev' and 'count' fields in "struct net".

'count' is written each time a socket is created or destroyed, while
loopback_dev might be often read in routing code.

Move loopback_dev in a read mostly section of "struct net"

Note: struct netns_xfrm is cache line aligned on SMP.
(It contains a "struct dst_ops")
Move it at the end to avoid holes, and reduce sizeof(struct net) by 128
bytes on ia32.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 7 deletions

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index bd10a7908993..65af9a07cf76 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -41,6 +41,8 @@ struct net {
                                                  * destroy on demand
                                                  */
 #endif
+        spinlock_t              rules_mod_lock;
+
         struct list_head        list;           /* list of network namespaces */
         struct list_head        cleanup_list;   /* namespaces on death row */
         struct list_head        exit_list;      /* Use only net_mutex */
@@ -52,7 +54,8 @@ struct net {
         struct ctl_table_set    sysctls;
 #endif
 
-        struct net_device       *loopback_dev;          /* The loopback */
+        struct sock             *rtnl;                  /* rtnetlink socket */
+        struct sock             *genl_sock;
 
         struct list_head        dev_base_head;
         struct hlist_head       *dev_name_head;
@@ -60,11 +63,9 @@ struct net {
 
         /* core fib_rules */
         struct list_head        rules_ops;
-        spinlock_t              rules_mod_lock;
 
-        struct sock             *rtnl;                  /* rtnetlink socket */
-        struct sock             *genl_sock;
 
+        struct net_device       *loopback_dev;          /* The loopback */
         struct netns_core       core;
         struct netns_mib        mib;
         struct netns_packet     packet;
@@ -84,13 +85,15 @@ struct net {
         struct sock             *nfnl;
         struct sock             *nfnl_stash;
 #endif
-#ifdef CONFIG_XFRM
-        struct netns_xfrm       xfrm;
-#endif
 #ifdef CONFIG_WEXT_CORE
         struct sk_buff_head     wext_nlevents;
 #endif
         struct net_generic      *gen;
+
+        /* Note : following structs are cache line aligned */
+#ifdef CONFIG_XFRM
+        struct netns_xfrm       xfrm;
+#endif
 };