[NETEM]: avoid excessive requeues
Stephen Hemminger [Thu, 22 Mar 2007 19:17:42 +0000 (12:17 -0700)]
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>

net/sched/sch_api.c
net/sched/sch_netem.c

index b06f202..fcaa4ad 100644 (file)
@@ -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);
 
index 7e9e658..fb49e9e 100644 (file)
@@ -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;