David Miller a écrit :
> From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> Date: Thu, 4 Jun 2009 13:24:57 +0930
>
>> On Thu, 4 Jun 2009 06:32:53 am Eric Dumazet wrote:
>>> 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
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