Commit ef647f13 authored Aug 05, 2008 by Stephen Hemminger Committed by David S. Miller Aug 05, 2008

bridge: Eliminate unnecessary forward delay



From: Stephen Hemminger <shemminger@vyatta.com>

Based upon original patch by Herbert Xu, which contained
the following problem description:

--------------------
When the forward delay is set to zero, we still delay the setting
of the forwarding state by one or possibly two timers depending
on whether STP is enabled.  This could either turn out to be
instantaneous, or horribly slow depending on the load of the
machine.

As there is nothing preventing us from enabling forwarding straight
away, this patch eliminates this potential delay by executing the
code directly if the forward delay is zero.

The effect of this problem is that immediately after the carrier
comes on a port, the bridge will drop all packets received from
that port until it enters forwarding mode, thus causing unnecessary
packet loss.

Note that this patch doesn't fully remove the delay due to the
link watcher.  We should also check the carrier state when we
are about to drop an incoming packet because the port is disabled.
But that's for another patch.
--------------------

This version of the fix takes a different approach, in that
it just does the state change directly.

Signed-off-by: David S. Miller <davem@davemloft.net>

parent 33e33495

net/bridge/br_stp.c

+18 −7

Original line number	Original line	Diff line number	Diff line
	@@ -368,14 +368,25 @@ static void br_make_blocking(struct net_bridge_port *p)
	/* called under bridge lock */		/* called under bridge lock */
	static void br_make_forwarding(struct net_bridge_port *p)		static void br_make_forwarding(struct net_bridge_port *p)
	{		{
	if (p->state == BR_STATE_BLOCKING) {		struct net_bridge *br = p->br;
	if (p->br->stp_enabled == BR_KERNEL_STP)
			if (p->state != BR_STATE_BLOCKING)
			return;

			if (br->forward_delay == 0) {
			p->state = BR_STATE_FORWARDING;
			br_topology_change_detection(br);
			del_timer(&p->forward_delay_timer);
			}
			else if (p->br->stp_enabled == BR_KERNEL_STP)
	p->state = BR_STATE_LISTENING;		p->state = BR_STATE_LISTENING;
	else		else
	p->state = BR_STATE_LEARNING;		p->state = BR_STATE_LEARNING;

	br_log_state(p);		br_log_state(p);
	mod_timer(&p->forward_delay_timer, jiffies + p->br->forward_delay); }
			if (br->forward_delay != 0)
			mod_timer(&p->forward_delay_timer, jiffies + br->forward_delay);
	}		}

	/* called under bridge lock */		/* called under bridge lock */

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