Linux Ethernet Bridging - Apr 2019 - [Bridge] [PATCH net-next] net: bridge: optimize backup_port fdb convergence

We can optimize the fdb convergence when a backup_port is present by not
immediately flushing the entries of the stopped port since traffic for
those entries will flow towards the backup_port.

There are 2 cases specifically that benefit most:
- when the stopped port comes up before the entries expire by themselves
- when there's an external entry refresh and they're kept while the
  backup_port is operating (e.g. mlag)

Signed-off-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
---
We have been running with this change for over an year, it has been
extensively tested.

 net/bridge/br_stp_if.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 808e2b914015..8d65ae5210e0 100644
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -117,7 +117,8 @@ void br_stp_disable_port(struct net_bridge_port *p)
 	del_timer(&p->forward_delay_timer);
 	del_timer(&p->hold_timer);
 
-	br_fdb_delete_by_port(br, p, 0, 0);
+	if (!rcu_access_pointer(p->backup_port))
+		br_fdb_delete_by_port(br, p, 0, 0);
 	br_multicast_disable_port(p);
 
 	br_configuration_update(br);
-- 
2.20.1

From: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
Date: Wed,  3 Apr 2019 13:49:24 +0300
> We can optimize the fdb convergence when a backup_port is present by not
> immediately flushing the entries of the stopped port since traffic for
> those entries will flow towards the backup_port.
> 
> There are 2 cases specifically that benefit most:
> - when the stopped port comes up before the entries expire by themselves
> - when there's an external entry refresh and they're kept while the
>   backup_port is operating (e.g. mlag)
> 
> Signed-off-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
Applied.