[BRIDGE]: Reduce frequency of forwarding cleanup timer in bridge.

The bridge cleanup timer is fired 10 times a second for timers that
are at least 15 seconds ahead in time and that are not critical to be
cleaned asap.

This patch calculates the next time to run the timer as the minimum of
all timers or a minimum based on the current state.
Signed-off-by: Baruch Even <baruch@ev-en.org>
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_fdb.c

@@ -121,6 +121,7 @@ void br_fdb_cleanup(unsigned long _data)
 {
 	struct net_bridge *br = (struct net_bridge *)_data;
 	unsigned long delay = hold_time(br);
+	unsigned long next_timer = jiffies + br->forward_delay;
 	int i;
 
 	spin_lock_bh(&br->hash_lock);
@@ -129,14 +130,21 @@ void br_fdb_cleanup(unsigned long _data)
 		struct hlist_node *h, *n;
 
 		hlist_for_each_entry_safe(f, h, n, &br->hash[i], hlist) {
-			if (!f->is_static &&
-			    time_before_eq(f->ageing_timer + delay, jiffies))
+			unsigned long this_timer;
+			if (f->is_static)
+				continue;
+			this_timer = f->ageing_timer + delay;
+			if (time_before_eq(this_timer, jiffies))
 				fdb_delete(f);
+			else if (this_timer < next_timer)
+				next_timer = this_timer;
 		}
 	}
 	spin_unlock_bh(&br->hash_lock);
 
-	mod_timer(&br->gc_timer, jiffies + HZ/10);
+	/* Add HZ/4 to ensure we round the jiffies upwards to be after the next
+	 * timer, otherwise we might round down and will have no-op run. */
+	mod_timer(&br->gc_timer, round_jiffies(next_timer + HZ/4));
 }
 
 /* Completely flush all dynamic entries in forwarding database.*/