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net: speedup udp receive path 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/net/sock.h
View File

@ -1021,6 +1021,16 @@ extern void release_sock(struct sock *sk);
SINGLE_DEPTH_NESTING)
#define bh_unlock_sock(__sk) spin_unlock(&((__sk)->sk_lock.slock))
static inline void lock_sock_bh(struct sock *sk)
{
spin_lock_bh(&sk->sk_lock.slock);
}
static inline void unlock_sock_bh(struct sock *sk)
{
spin_unlock_bh(&sk->sk_lock.slock);
}
extern struct sock *sk_alloc(struct net *net, int family,
gfp_t priority,
struct proto *prot);

10
net/core/datagram.c
View File

@ -229,9 +229,13 @@ EXPORT_SYMBOL(skb_free_datagram);
void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
{
lock_sock(sk);
skb_free_datagram(sk, skb);
release_sock(sk);
lock_sock_bh(sk);
skb_orphan(skb);
sk_mem_reclaim_partial(sk);
unlock_sock_bh(sk);
/* skb is now orphaned, might be freed outside of locked section */
consume_skb(skb);
}
EXPORT_SYMBOL(skb_free_datagram_locked);

12
net/ipv4/udp.c
View File

@ -1062,10 +1062,10 @@ static unsigned int first_packet_length(struct sock *sk)
spin_unlock_bh(&rcvq->lock);
if (!skb_queue_empty(&list_kill)) {
lock_sock(sk);
lock_sock_bh(sk);
__skb_queue_purge(&list_kill);
sk_mem_reclaim_partial(sk);
release_sock(sk);
unlock_sock_bh(sk);
}
return res;
}
@ -1196,10 +1196,10 @@ out:
return err;
csum_copy_err:
lock_sock(sk);
lock_sock_bh(sk);
if (!skb_kill_datagram(sk, skb, flags))
UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
release_sock(sk);
unlock_sock_bh(sk);
if (noblock)
return -EAGAIN;
@ -1624,9 +1624,9 @@ int udp_rcv(struct sk_buff *skb)
void udp_destroy_sock(struct sock *sk)
{
lock_sock(sk);
lock_sock_bh(sk);
udp_flush_pending_frames(sk);
release_sock(sk);
unlock_sock_bh(sk);
}
/*

4
net/ipv6/udp.c
View File

@ -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;