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net: speedup udp receive path

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Since commit 95766fff ([UDP]: Add memory accounting.), 
each received packet needs one extra sock_lock()/sock_release() pair.

This added latency because of possible backlog handling. Then later,
ticket spinlocks added yet another latency source in case of DDOS.

This patch introduces lock_sock_bh() and unlock_sock_bh()
synchronization primitives, avoiding one atomic operation and backlog
processing.

skb_free_datagram_locked() uses them instead of full blown
lock_sock()/release_sock(). skb is orphaned inside locked section for
proper socket memory reclaim, and finally freed outside of it.

UDP receive path now take the socket spinlock only once.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2010-04-28 14:35:48 -07:00
committed by David S. Miller
parent cfc1fbb079
commit 4b0b72f7dd
4 changed files with 25 additions and 11 deletions
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4
net/ipv6/udp.c
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@@ -424,7 +424,7 @@ out:
return err;
csum_copy_err:
lock_sock(sk);
lock_sock_bh(sk);
if (!skb_kill_datagram(sk, skb, flags)) {
if (is_udp4)
UDP_INC_STATS_USER(sock_net(sk),
@@ -433,7 +433,7 @@ csum_copy_err:
UDP6_INC_STATS_USER(sock_net(sk),
UDP_MIB_INERRORS, is_udplite);
}
release_sock(sk);
unlock_sock_bh(sk);
if (flags & MSG_DONTWAIT)
return -EAGAIN;