net_sched: gred: actually perform idling in WRED mode

gred_dequeue() and gred_drop() do not seem to get called when the
queue is empty, meaning that we never start idling while in WRED
mode. And since qidlestart is not stored by gred_store_wred_set(),
we would never stop idling while in WRED mode if we ever started.
This messes up the average queue size calculation that influences
packet marking/dropping behavior.

Now, we start WRED mode idling as we are removing the last packet
from the queue. Also we now actually stop WRED mode idling when we
are enqueuing a packet.

Cc: Bruce Osler <brosler@cisco.com>
Signed-off-by: David Ward <david.ward@ll.mit.edu>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_gred.c

@@ -136,6 +136,7 @@ static inline void gred_store_wred_set(struct gred_sched *table,
 				       struct gred_sched_data *q)
 {
 	table->wred_set.qavg = q->vars.qavg;
+	table->wred_set.qidlestart = q->vars.qidlestart;
 }
 
 static inline int gred_use_ecn(struct gred_sched *t)
@@ -259,16 +260,18 @@ static struct sk_buff *gred_dequeue(struct Qdisc *sch)
 		} else {
 			q->backlog -= qdisc_pkt_len(skb);
 
-			if (!q->backlog && !gred_wred_mode(t))
+			if (gred_wred_mode(t)) {
+				if (!sch->qstats.backlog)
+					red_start_of_idle_period(&t->wred_set);
+			} else {
+				if (!q->backlog)
 					red_start_of_idle_period(&q->vars);
 			}
+		}
 
 		return skb;
 	}
 
-	if (gred_wred_mode(t) && !red_is_idling(&t->wred_set))
-		red_start_of_idle_period(&t->wred_set);
-
 	return NULL;
 }
 
@@ -290,19 +293,20 @@ static unsigned int gred_drop(struct Qdisc *sch)
 			q->backlog -= len;
 			q->stats.other++;
 
-			if (!q->backlog && !gred_wred_mode(t))
+			if (gred_wred_mode(t)) {
+				if (!sch->qstats.backlog)
+					red_start_of_idle_period(&t->wred_set);
+			} else {
+				if (!q->backlog)
 					red_start_of_idle_period(&q->vars);
 			}
+		}
 
 		qdisc_drop(skb, sch);
 		return len;
 	}
 
-	if (gred_wred_mode(t) && !red_is_idling(&t->wred_set))
-		red_start_of_idle_period(&t->wred_set);
-
 	return 0;
-
 }
 
 static void gred_reset(struct Qdisc *sch)