netdev - [PATCH RFC] pkt_sched: Remove smp_wmb() in qdisc

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Message-ID: <20081219113047.GA17826@ff.dom.local>
Date:	Fri, 19 Dec 2008 11:30:47 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: [PATCH RFC] 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.

Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
---

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

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 6bc29e8..0fc4a18 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -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;
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 7e78f1c..d876b87 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -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;
 
--
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