Hi David
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 :) )
Thank you
Signed-off-by: Eric Dumazet <[EMAIL PROTECTED]>
--- linux/include/net/sock.h 2007-02-22 16:21:36.000000000 +0100
+++ linux-ed/include/net/sock.h 2007-02-22 16:21:36.000000000 +0100
@@ -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;
--- linux/net/core/sock.c 2007-02-22 16:21:36.000000000 +0100
+++ linux-ed/net/core/sock.c 2007-02-22 16:21:36.000000000 +0100
@@ -904,6 +904,7 @@ struct sock *sk_clone(const struct sock
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
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);
