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>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index ac2ea73..3431074 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1355,7 +1355,7 @@
}
/* 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 @@
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 @@
}
bh_unlock_sock(sk);
+put_and_return:
sock_put(sk);
return ret;