David Miller a écrit :

From: Rusty Russell <redacted>
Date: Thu, 4 Jun 2009 13:24:57 +0930

quoted

On Thu, 4 Jun 2009 06:32:53 am Eric Dumazet wrote:

quoted

Also, taking a reference on socket for each xmit packet in flight is very
expensive, since it slows down receiver in __udp4_lib_lookup(). Several
cpus are fighting for sk->refcnt cache line.

Now we have decent dynamic per-cpu, we can finally implement bigrefs.  More 
obvious for device counts than sockets, but perhaps applicable here as well?

It might be very beneficial for longer lasting, active, connections, but
for high connection rates it's going to be a lose in my estimation.

Agreed.

We also can avoid the sock_put()/sock_hold() pair for each tx packet,
to only touch sk_wmem_alloc (with appropriate atomic_sub_return() in sock_wfree()
and atomic_dec_test in sk_free

We could initialize sk->sk_wmem_alloc to one instead of 0, so that
sock_wfree() could just synchronize itself with sk_free()

void sk_free(struct sock *sk)
{
	if (atomic_dec_test(&sk->sk_wmem_alloc))
		__sk_free(sk)
}

 static inline void skb_set_owner_w(struct sk_buff *skb, struct sock *sk)
 {
-       sock_hold(sk);
        skb->sk = sk;
        skb->destructor = sock_wfree;
        atomic_add(skb->truesize, &sk->sk_wmem_alloc);
 }

 void sock_wfree(struct sk_buff *skb)
 {
        struct sock *sk = skb->sk;
+       int res;

        /* In case it might be waiting for more memory. */
-       atomic_sub(skb->truesize, &sk->sk_wmem_alloc);
+       res = atomic_sub_return(skb->truesize, &sk->sk_wmem_alloc);
        if (!sock_flag(sk, SOCK_USE_WRITE_QUEUE))
                sk->sk_write_space(sk);
-       sock_put(sk);
+       if (res == 0)
+               __sk_free(sk);
 }

Patch will follow after some testing