[PATCH net] netlink: move nl_table in read_mostly section

[PATCH net] netlink: move nl_table in read_mostly section

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

netlink sockets creation and deletion heavily modify nl_table_users
and nl_table_lock.

If nl_table is sharing one cache line with one of them, netlink
performance is really bad on SMP.

ffffffff81ff5f00 B nl_table
ffffffff81ff5f0c b nl_table_users

Putting nl_table in read_mostly section increased performance
of my open/delete netlink sockets test by about 80 %

This came up while diagnosing a getaddrinfo() problem.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/netlink/af_netlink.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index daa0b818174b..dbe885901b34 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -89,7 +89,7 @@ static inline int netlink_is_kernel(struct sock *sk)
 	return nlk_sk(sk)->flags & NETLINK_KERNEL_SOCKET;
 }
 
-struct netlink_table *nl_table;
+struct netlink_table *nl_table __read_mostly;
 EXPORT_SYMBOL_GPL(nl_table);
 
 static DECLARE_WAIT_QUEUE_HEAD(nl_table_wait);

Re: [PATCH net] netlink: move nl_table in read_mostly section

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 12 May 2015 17:24:50 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> netlink sockets creation and deletion heavily modify nl_table_users
> and nl_table_lock.
> 
> If nl_table is sharing one cache line with one of them, netlink
> performance is really bad on SMP.
> 
> ffffffff81ff5f00 B nl_table
> ffffffff81ff5f0c b nl_table_users
> 
> Putting nl_table in read_mostly section increased performance
> of my open/delete netlink sockets test by about 80 %
> 
> This came up while diagnosing a getaddrinfo() problem.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied, thanks Eric.