[PATCH] TBF: stop qdisc infanticide

[PATCH] TBF: stop qdisc infanticide

[Stephen Hemminger]

Several netem users have complained that when using TBF for rate control
that any change to TBF parameters destroys the child qdisc. A typical
use is to have a test that sets up netem + TBF then changes bandwidth
setting.  But every time the parameters of TBF are changed it destroys
the child qdisc, requiring reconfiguration. Other qdisc's like HTB
don't do this.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>


--- a/net/sched/sch_tbf.c	2010-05-12 20:41:06.257006386 -0700
+++ b/net/sched/sch_tbf.c	2010-05-12 20:52:35.671216316 -0700
@@ -273,7 +273,11 @@ static int tbf_change(struct Qdisc* sch,
 	if (max_size < 0)
 		goto done;
 
-	if (qopt->limit > 0) {
+	if (q->qdisc) {
+		err = fifo_set_limit(q->qdisc, qopt->limit);
+		if (err)
+			goto done;
+	} else if (qopt->limit > 0) {
 		child = fifo_create_dflt(sch, &bfifo_qdisc_ops, qopt->limit);
 		if (IS_ERR(child)) {
 			err = PTR_ERR(child);

Re: [PATCH] TBF: stop qdisc infanticide

[Patrick McHardy]

Stephen Hemminger wrote:
> Several netem users have complained that when using TBF for rate control
> that any change to TBF parameters destroys the child qdisc. A typical
> use is to have a test that sets up netem + TBF then changes bandwidth
> setting.  But every time the parameters of TBF are changed it destroys
> the child qdisc, requiring reconfiguration. Other qdisc's like HTB
> don't do this.
> 
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> 
> 
> --- a/net/sched/sch_tbf.c	2010-05-12 20:41:06.257006386 -0700
> +++ b/net/sched/sch_tbf.c	2010-05-12 20:52:35.671216316 -0700
> @@ -273,7 +273,11 @@ static int tbf_change(struct Qdisc* sch,
>  	if (max_size < 0)
>  		goto done;
>  
> -	if (qopt->limit > 0) {
> +	if (q->qdisc) {
> +		err = fifo_set_limit(q->qdisc, qopt->limit);
> +		if (err)
> +			goto done;

q->qdisc is never NULL since a noop_qdisc is assigned by default. Also
this should check that the child is in fact one of the *fifos.

> +	} else if (qopt->limit > 0) {
>  		child = fifo_create_dflt(sch, &bfifo_qdisc_ops, qopt->limit);
>  		if (IS_ERR(child)) {
>  			err = PTR_ERR(child);
> 

Re: [PATCH] TBF: stop qdisc infanticide

[Stephen Hemminger]

On Thu, 13 May 2010 18:22:56 +0200
Patrick McHardy <kaber@trash.net> wrote:

> Stephen Hemminger wrote:
> > Several netem users have complained that when using TBF for rate control
> > that any change to TBF parameters destroys the child qdisc. A typical
> > use is to have a test that sets up netem + TBF then changes bandwidth
> > setting.  But every time the parameters of TBF are changed it destroys
> > the child qdisc, requiring reconfiguration. Other qdisc's like HTB
> > don't do this.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> > 
> > 
> > --- a/net/sched/sch_tbf.c	2010-05-12 20:41:06.257006386 -0700
> > +++ b/net/sched/sch_tbf.c	2010-05-12 20:52:35.671216316 -0700
> > @@ -273,7 +273,11 @@ static int tbf_change(struct Qdisc* sch,
> >  	if (max_size < 0)
> >  		goto done;
> >  
> > -	if (qopt->limit > 0) {
> > +	if (q->qdisc) {
> > +		err = fifo_set_limit(q->qdisc, qopt->limit);
> > +		if (err)
> > +			goto done;
> 
> q->qdisc is never NULL since a noop_qdisc is assigned by default. Also
> this should check that the child is in fact one of the *fifos.

But the child will be netem and fifo_set_limit ignores non-fifo.

Re: [PATCH] TBF: stop qdisc infanticide

[Patrick McHardy]

Stephen Hemminger wrote:
> On Thu, 13 May 2010 18:22:56 +0200
> Patrick McHardy <kaber@trash.net> wrote:
> 
>> Stephen Hemminger wrote:
>>> Several netem users have complained that when using TBF for rate control
>>> that any change to TBF parameters destroys the child qdisc. A typical
>>> use is to have a test that sets up netem + TBF then changes bandwidth
>>> setting.  But every time the parameters of TBF are changed it destroys
>>> the child qdisc, requiring reconfiguration. Other qdisc's like HTB
>>> don't do this.
>>>
>>> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>>>
>>>
>>> --- a/net/sched/sch_tbf.c	2010-05-12 20:41:06.257006386 -0700
>>> +++ b/net/sched/sch_tbf.c	2010-05-12 20:52:35.671216316 -0700
>>> @@ -273,7 +273,11 @@ static int tbf_change(struct Qdisc* sch,
>>>  	if (max_size < 0)
>>>  		goto done;
>>>  
>>> -	if (qopt->limit > 0) {
>>> +	if (q->qdisc) {
>>> +		err = fifo_set_limit(q->qdisc, qopt->limit);
>>> +		if (err)
>>> +			goto done;
>> q->qdisc is never NULL since a noop_qdisc is assigned by default. Also
>> this should check that the child is in fact one of the *fifos.
> 
> But the child will be netem and fifo_set_limit ignores non-fifo.

OK, but it does need to make sure the child is not a noop_qdisc,
otherwise it won't create the default bfifo.

[PATCH] tbf: stop wanton destruction of children (v2)

[Stephen Hemminger]

Several netem users use TBF for rate control. But every time the parameters
of TBF are changed it destroys the child qdisc, requiring reconfigation.
Better to just keep child qdisc and just notify it of changed limit.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>


--- a/net/sched/sch_tbf.c	2010-05-14 15:04:56.297095729 -0700
+++ b/net/sched/sch_tbf.c	2010-05-14 15:09:57.296733332 -0700
@@ -273,7 +273,11 @@ static int tbf_change(struct Qdisc* sch,
 	if (max_size < 0)
 		goto done;
 
-	if (qopt->limit > 0) {
+	if (q->qdisc != &noop_qdisc) {
+		err = fifo_set_limit(q->qdisc, qopt->limit);
+		if (err)
+			goto done;
+	} else if (qopt->limit > 0) {
 		child = fifo_create_dflt(sch, &bfifo_qdisc_ops, qopt->limit);
 		if (IS_ERR(child)) {
 			err = PTR_ERR(child);