From aa1039e73cc2cf834e99c09d2033d5d2675357b9 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 15 Jun 2010 08:23:14 +0000 Subject: inetpeer: RCU conversion inetpeer currently uses an AVL tree protected by an rwlock. It's possible to make most lookups use RCU 1) Add a struct rcu_head to struct inet_peer 2) add a lookup_rcu_bh() helper to perform lockless and opportunistic lookup. This is a normal function, not a macro like lookup(). 3) Add a limit to number of links followed by lookup_rcu_bh(). This is needed in case we fall in a loop. 4) add an smp_wmb() in link_to_pool() right before node insert. 5) make unlink_from_pool() use atomic_cmpxchg() to make sure it can take last reference to an inet_peer, since lockless readers could increase refcount, even while we hold peers.lock. 6) Delay struct inet_peer freeing after rcu grace period so that lookup_rcu_bh() cannot crash. 7) inet_getpeer() first attempts lockless lookup. Note this lookup can fail even if target is in AVL tree, but a concurrent writer can let tree in a non correct form. If this attemps fails, lock is taken a regular lookup is performed again. 8) convert peers.lock from rwlock to a spinlock 9) Remove SLAB_HWCACHE_ALIGN when peer_cachep is created, because rcu_head adds 16 bytes on 64bit arches, doubling effective size (64 -> 128 bytes) In a future patch, this is probably possible to revert this part, if rcu field is put in an union to share space with rid, ip_id_count, tcp_ts & tcp_ts_stamp. These fields being manipulated only with refcnt > 0. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/net/inetpeer.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h index 87b1df0d4d8..61740473042 100644 --- a/include/net/inetpeer.h +++ b/include/net/inetpeer.h @@ -26,6 +26,7 @@ struct inet_peer { atomic_t ip_id_count; /* IP ID for the next packet */ __u32 tcp_ts; __u32 tcp_ts_stamp; + struct rcu_head rcu; }; void inet_initpeers(void) __init; -- cgit v1.2.3-70-g09d2