[NET]: Keep sk_backlog near sk_lock

sk_backlog is a critical field of struct sock. (known famous words)

It is (ab)used in hot paths, in particular in release_sock(), tcp_recvmsg(),
tcp_v4_rcv(), sk_receive_skb().

It really makes sense to place it next to sk_lock, because sk_backlog is only
used after sk_lock locked (and thus memory cache line in L1 cache). This
should reduce cache misses and sk_lock acquisition time.

(In theory, we could only move the head pointer near sk_lock, and leaving tail
far away, because 'tail' is normally not so hot, but keep it simple :) )

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

2 files changed, 10 insertions, 10 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index 2c7d60ca3548..a3366c3c837a 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -202,6 +202,15 @@ struct sock {
         unsigned short          sk_type;
         int                     sk_rcvbuf;
         socket_lock_t           sk_lock;
+        /*
+         * The backlog queue is special, it is always used with
+         * the per-socket spinlock held and requires low latency
+         * access. Therefore we special case it's implementation.
+         */
+        struct {
+                struct sk_buff *head;
+                struct sk_buff *tail;
+        } sk_backlog;
         wait_queue_head_t       *sk_sleep;
         struct dst_entry        *sk_dst_cache;
         struct xfrm_policy      *sk_policy[2];
@@ -221,15 +230,6 @@ struct sock {
         int                     sk_rcvlowat;
         unsigned long           sk_flags;
         unsigned long           sk_lingertime;
-        /*
-         * The backlog queue is special, it is always used with
-         * the per-socket spinlock held and requires low latency
-         * access. Therefore we special case it's implementation.
-         */
-        struct {
-                struct sk_buff *head;
-                struct sk_buff *tail;
-        } sk_backlog;
         struct sk_buff_head     sk_error_queue;
         struct proto            *sk_prot_creator;
         rwlock_t                sk_callback_lock;
diff --git a/net/core/sock.c b/net/core/sock.c
index 27c4f62382bd..6d35d5775ba8 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -904,6 +904,7 @@ struct sock *sk_clone(const struct sock *sk, const gfp_t priority)
                 sk_node_init(&newsk->sk_node);
                 sock_lock_init(newsk);
                 bh_lock_sock(newsk);
+                newsk->sk_backlog.head  = newsk->sk_backlog.tail = NULL;
 
                 atomic_set(&newsk->sk_rmem_alloc, 0);
                 atomic_set(&newsk->sk_wmem_alloc, 0);
@@ -923,7 +924,6 @@ struct sock *sk_clone(const struct sock *sk, const gfp_t priority)
                 newsk->sk_wmem_queued   = 0;
                 newsk->sk_forward_alloc = 0;
                 newsk->sk_send_head     = NULL;
-                newsk->sk_backlog.head  = newsk->sk_backlog.tail = NULL;
                 newsk->sk_userlocks     = sk->sk_userlocks & ~SOCK_BINDPORT_LOCK;
 
                 sock_reset_flag(newsk, SOCK_DONE);