[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>

diff --git a/include/net/sock.h b/include/net/sock.h
index 2c7d60c..a3366c3 100644 (file)
--- 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 27c4f62..6d35d57 100644 (file)
--- 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);