[NETEM]: avoid excessive requeues

The netem code would call getnstimeofday() and dequeue/requeue after
every packet, even if it was waiting. Avoid this overhead by using
the throttled flag.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 16 insertions, 10 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index b06f20294ac0..fcaa4adefc82 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -298,6 +298,7 @@ static enum hrtimer_restart qdisc_watchdog(struct hrtimer *timer)
                                                  timer);
 
         wd->qdisc->flags &= ~TCQ_F_THROTTLED;
+        smp_wmb();
         netif_schedule(wd->qdisc->dev);
         return HRTIMER_NORESTART;
 }
@@ -315,6 +316,7 @@ void qdisc_watchdog_schedule(struct qdisc_watchdog *wd, psched_time_t expires)
         ktime_t time;
 
         wd->qdisc->flags |= TCQ_F_THROTTLED;
+        smp_wmb();
         time = ktime_set(0, 0);
         time = ktime_add_ns(time, PSCHED_US2NS(expires));
         hrtimer_start(&wd->timer, time, HRTIMER_MODE_ABS);
@@ -325,6 +327,7 @@ void qdisc_watchdog_cancel(struct qdisc_watchdog *wd)
 {
         hrtimer_cancel(&wd->timer);
         wd->qdisc->flags &= ~TCQ_F_THROTTLED;
+        smp_wmb();
 }
 EXPORT_SYMBOL(qdisc_watchdog_cancel);
 
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 7e9e658d4d93..fb49e9e7ace0 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -273,6 +273,10 @@ 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;
+
         skb = q->qdisc->dequeue(q->qdisc);
         if (skb) {
                 const struct netem_skb_cb *cb
@@ -285,18 +289,17 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
                 if (PSCHED_TLESS(cb->time_to_send, now)) {
                         pr_debug("netem_dequeue: return skb=%p\n", skb);
                         sch->q.qlen--;
-                        sch->flags &= ~TCQ_F_THROTTLED;
                         return skb;
-                } else {
-                        qdisc_watchdog_schedule(&q->watchdog, cb->time_to_send);
-
-                        if (q->qdisc->ops->requeue(skb, q->qdisc) != NET_XMIT_SUCCESS) {
-                                qdisc_tree_decrease_qlen(q->qdisc, 1);
-                                sch->qstats.drops++;
-                                printk(KERN_ERR "netem: queue discpline %s could not requeue\n",
-                                       q->qdisc->ops->id);
-                        }
                 }
+
+                if (unlikely(q->qdisc->ops->requeue(skb, q->qdisc) != NET_XMIT_SUCCESS)) {
+                        qdisc_tree_decrease_qlen(q->qdisc, 1);
+                        sch->qstats.drops++;
+                        printk(KERN_ERR "netem: %s could not requeue\n",
+                               q->qdisc->ops->id);
+                }
+
+                qdisc_watchdog_schedule(&q->watchdog, cb->time_to_send);
         }
 
         return NULL;