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tcp: do not lock listener to process SYN packets 

Everything should now be ready to finally allow SYN
packets processing without holding listener lock.

Tested:

3.5 Mpps SYNFLOOD. Plenty of cpu cycles available.

Next bottleneck is the refcount taken on listener,
that could be avoided if we remove SLAB_DESTROY_BY_RCU
strict semantic for listeners, and use regular RCU.

    13.18%  [kernel]  [k] __inet_lookup_listener
     9.61%  [kernel]  [k] tcp_conn_request
     8.16%  [kernel]  [k] sha_transform
     5.30%  [kernel]  [k] inet_reqsk_alloc
     4.22%  [kernel]  [k] sock_put
     3.74%  [kernel]  [k] tcp_make_synack
     2.88%  [kernel]  [k] ipt_do_table
     2.56%  [kernel]  [k] memcpy_erms
     2.53%  [kernel]  [k] sock_wfree
     2.40%  [kernel]  [k] tcp_v4_rcv
     2.08%  [kernel]  [k] fib_table_lookup
     1.84%  [kernel]  [k] tcp_openreq_init_rwin

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-10-02 11:43:39 -07:00 committed by David S. Miller
parent 92d6f176fd
commit e994b2f0fb
2 changed files with 18 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
net/ipv4/tcp_ipv4.c
View File

@ -1355,7 +1355,7 @@ static struct sock *tcp_v4_cookie_check(struct sock *sk, struct sk_buff *skb)
}
/* The socket must have it's spinlock held when we get
* here.
* here, unless it is a TCP_LISTEN socket.
*
* We have a potential double-lock case here, so even when
* doing backlog processing we use the BH locking scheme.
@ -1619,9 +1619,15 @@ process:
if (sk_filter(sk, skb))
goto discard_and_relse;
sk_incoming_cpu_update(sk);
skb->dev = NULL;
if (sk->sk_state == TCP_LISTEN) {
ret = tcp_v4_do_rcv(sk, skb);
goto put_and_return;
}
sk_incoming_cpu_update(sk);
bh_lock_sock_nested(sk);
tcp_sk(sk)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
ret = 0;
@ -1636,6 +1642,7 @@ process:
}
bh_unlock_sock(sk);
put_and_return:
sock_put(sk);
return ret;

11
net/ipv6/tcp_ipv6.c
View File

@ -1161,7 +1161,7 @@ out:
}
/* The socket must have it's spinlock held when we get
* here.
* here, unless it is a TCP_LISTEN socket.
*
* We have a potential double-lock case here, so even when
* doing backlog processing we use the BH locking scheme.
@ -1415,9 +1415,15 @@ process:
if (sk_filter(sk, skb))
goto discard_and_relse;
sk_incoming_cpu_update(sk);
skb->dev = NULL;
if (sk->sk_state == TCP_LISTEN) {
ret = tcp_v6_do_rcv(sk, skb);
goto put_and_return;
}
sk_incoming_cpu_update(sk);
bh_lock_sock_nested(sk);
tcp_sk(sk)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
ret = 0;
@ -1432,6 +1438,7 @@ process:
}
bh_unlock_sock(sk);
put_and_return:
sock_put(sk);
return ret ? -1 : 0;