pkt_sched: Remove smp_wmb() in qdisc_watchdog()

Hi,

I hope Stephen will find a minute to reconsider and/or comment this a bit.

Thanks,
Jarek P.
---------->

While implementing a TCQ_F_THROTTLED flag there was used an smp_wmb() in qdisc_watchdog(), but since this flag is practically used only in sch_netem(), and since it's not even clear what reordering is avoided here (TCQ_F_THROTTLED vs. __QDISC_STATE_SCHED?) it seems the barrier could be safely removed.

---

 net/sched/sch_api.c   |    1 -
 net/sched/sch_netem.c |    1 -
 2 files changed, 0 insertions(+), 2 deletions(-)

index 6bc29e8..0fc4a18 100644
@@ -450,7 +450,6 @@ static enum hrtimer_restart qdisc_watchdog(struct hrtimer *timer)
 						 timer);
 
 	wd->qdisc->flags &= ~TCQ_F_THROTTLED;
-	smp_wmb();
 	__netif_schedule(qdisc_root(wd->qdisc));
 
 	return HRTIMER_NORESTART;

index 7e78f1c..d876b87 100644
@@ -266,7 +266,6 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 	struct netem_sched_data *q = qdisc_priv(sch);
 	struct sk_buff *skb;
 
-	smp_mb();
 	if (sch->flags & TCQ_F_THROTTLED)
 		return NULL;
 

On Fri, Dec 19, 2008 at 11:30:47AM +0000, Jarek Poplawski wrote:
...

Hmm.. I forgot to mention sch_cbq(), but it doesn't use a barrier anyway.

Jarek P.

The barrier was copied from earlier version of tbf is unnecessary.

On Fri, Dec 19, 2008 at 06:18:51PM -0800, Stephen Hemminger wrote:
...

So I resend this patch with only a changelog updated

Thanks,
Jarek P.
---------->
While implementing a TCQ_F_THROTTLED flag there was used an smp_wmb() in qdisc_watchdog(). Stephen Hemminger acknowledged the barrier was copied from earlier version of tbf and is unnecessaray, so it's removed here.

---

 net/sched/sch_api.c   |    1 -
 net/sched/sch_netem.c |    1 -
 2 files changed, 0 insertions(+), 2 deletions(-)

index 6bc29e8..0fc4a18 100644
@@ -450,7 +450,6 @@ static enum hrtimer_restart qdisc_watchdog(struct hrtimer *timer)
 						 timer);
 
 	wd->qdisc->flags &= ~TCQ_F_THROTTLED;
-	smp_wmb();
 	__netif_schedule(qdisc_root(wd->qdisc));
 
 	return HRTIMER_NORESTART;

index 7e78f1c..d876b87 100644
@@ -266,7 +266,6 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 	struct netem_sched_data *q = qdisc_priv(sch);
 	struct sk_buff *skb;
 
-	smp_mb();
 	if (sch->flags & TCQ_F_THROTTLED)
 		return NULL;
 

From: Jarek Poplawski <[email protected]>
Date: Fri, 19 Dec 2008 11:30:47 +0000

Applied to net-next-2.6, thanks Jarek.