[LARTC] netem with prio hangs on duplicate

[LARTC] netem with prio hangs on duplicate

[js si]

hi

i tried the example given on the examples page to
duplicate selected traffic like

tc qdisc add dev eth0 root handle 1: prio
tc qdisc add dev eth0 parent 1:3 handle 3: netem
duplicate 40% 
tc filter add dev eth0 protocol ip parent 1:0 prio 3
u32 match ip dst 11.0.2.2 flowid 1:3

when i ping from 11.0.2.2 to this interface my machine
hangs. the same thing works for drop or delay. 

i would appreciate if someone can tell me what i am
doing wrong. 

thanks. 


		
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Re: [LARTC] netem with prio hangs on duplicate

[Patrick McHardy]

js si wrote:
> hi
> 
> i tried the example given on the examples page to
> duplicate selected traffic like
> 
> tc qdisc add dev eth0 root handle 1: prio
> tc qdisc add dev eth0 parent 1:3 handle 3: netem
> duplicate 40% 
> tc filter add dev eth0 protocol ip parent 1:0 prio 3
> u32 match ip dst 11.0.2.2 flowid 1:3
> 
> when i ping from 11.0.2.2 to this interface my machine
> hangs. the same thing works for drop or delay. 
> 
> i would appreciate if someone can tell me what i am
> doing wrong.

Using netem with an upper qdisc screws up the upper qdisc's
q.qlen counter and qdisc_run() tries to dequeue it indefinitely.
I don't know whether netem is intended to be useable only as
top-level qdisc, if so it should make sure that it really is
used this way to avoid hanging the system.

Regards
Patrick
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Re: [LARTC] netem with prio hangs on duplicate

[Stephen Hemminger]

On Wed, 30 Mar 2005 10:05:04 -0800 (PST)
js si <nistnet_user@yahoo.com> wrote:

> hi
> 
> i tried the example given on the examples page to
> duplicate selected traffic like
> 
> tc qdisc add dev eth0 root handle 1: prio
> tc qdisc add dev eth0 parent 1:3 handle 3: netem
> duplicate 40% 
> tc filter add dev eth0 protocol ip parent 1:0 prio 3
> u32 match ip dst 11.0.2.2 flowid 1:3
> 

Try this. qdisc_restart() has a bug. It will spin until packet becomes available, which
is wrong.  This effects both netem and tbf, maybe other qdisc as well.

--- linux-2.6/net/sched/sch_generic.c	2005-03-14 14:30:52.000000000 -0800
+++ tcp-2.6/net/sched/sch_generic.c	2005-04-04 10:28:31.000000000 -0700
@@ -176,10 +176,10 @@ int qdisc_restart(struct net_device *dev
 
 requeue:
 		q->ops->requeue(skb, q);
-		netif_schedule(dev);
-		return 1;
+		netif_schedule(dev);	
+		return q->q.qlen;
 	}
-	return q->q.qlen;
+	return 0;
 }
 
 static void dev_watchdog(unsigned long arg)
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