tree d01026afb4450ef685722cd7a0fe1815336170ca
parent 64153ce0a7b61b2a5cacb01805cbf670142339e9
author Eric Dumazet <edumazet@google.com> 1370620137 -0700
committer David S. Miller <davem@davemloft.net> 1371021923 -0700

igmp: hash a hash table to speedup ip_check_mc_rcu()

After IP route cache removal, multicast applications using
a lot of multicast addresses hit a O(N) behavior in ip_check_mc_rcu()

Add a per in_device hash table to get faster lookup.

This hash table is created only if the number of items in mc_list is
above 4.

Reported-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>