netlink: Convert netlink_lookup() to use RCU protected hash table

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 30%.

Also splits nl_table_lock into a separate mutex to protect hash table
mutations and allow synchronize_rcu() to sleep while waiting for readers
during expansion and shrinking.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Reviewed-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 14 deletions

diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d441f5b6..60f631fb7087 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;