Messages in this thread | | | Date | Mon, 06 Oct 2008 23:22:31 +0200 | From | Eric Dumazet <> | Subject | Re: [PATCH 3/3] Convert the UDP hash lock to RCU |
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Corey Minyard a écrit : > Change the UDP hash lock from an rwlock to RCU. > > Signed-off-by: Corey Minyard <cminyard@mvista.com> > --- > include/net/udp.h | 9 +++++---- > net/ipv4/udp.c | 47 +++++++++++++++++++++++++++-------------------- > net/ipv6/udp.c | 17 +++++++++-------- > 3 files changed, 41 insertions(+), 32 deletions(-) > > diff --git a/include/net/udp.h b/include/net/udp.h > index addcdc6..35aa104 100644 > --- a/include/net/udp.h > +++ b/include/net/udp.h > @@ -51,7 +51,7 @@ struct udp_skb_cb { > #define UDP_SKB_CB(__skb) ((struct udp_skb_cb *)((__skb)->cb)) > > extern struct hlist_head udp_hash[UDP_HTABLE_SIZE]; > -extern rwlock_t udp_hash_lock; > +extern spinlock_t udp_hash_wlock; > > > /* Note: this must match 'valbool' in sock_setsockopt */ > @@ -112,12 +112,13 @@ static inline void udp_lib_hash(struct sock *sk) > > static inline void udp_lib_unhash(struct sock *sk) > { > - write_lock_bh(&udp_hash_lock); > - if (sk_del_node_init(sk)) { > + spin_lock_bh(&udp_hash_wlock); > + if (sk_del_node_init_rcu(sk)) { > inet_sk(sk)->num = 0; > sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); > } > - write_unlock_bh(&udp_hash_lock); > + spin_unlock_bh(&udp_hash_wlock); > + synchronize_rcu();
UDP central rwlock can hurt performance, because of cache line ping pong, so your patch really makes sense.
Me wondering what impact this synchronize_rcu() can have on mono-threaded VOIP applications using lot of UDP sockets. What is the maximum delay of this function ?
For "struct file" freeing, we chose call_rcu() instead of synchronize_rcu()
Maybe we could add a generic rcu head to struct sock, and use call_rcu() in sk_prot_free() for sockets needing RCU (udp after your patch is applied, maybe tcp on future patches, while I believe previous work on the subject concluded RCU was not giving good results for short lived http sessions) ?
Or just add SLAB_DESTROY_BY_RCU to slab creation in proto_register() for "struct proto udp_prot/udpv6_prot" so that kmem_cache_free() done in sk_prot_free() can defer freeing to RCU...
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