net_sched: accurate bytes/packets stats/rates

In commit 44b8288308ac9d (net_sched: pfifo_head_drop problem), we fixed
a problem with pfifo_head drops that incorrectly decreased
sch->bstats.bytes and sch->bstats.packets

Several qdiscs (CHOKe, SFQ, pfifo_head, ...) are able to drop a
previously enqueued packet, and bstats cannot be changed, so
bstats/rates are not accurate (over estimated)

This patch changes the qdisc_bstats updates to be done at dequeue() time
instead of enqueue() time. bstats counters no longer account for dropped
frames, and rates are more correct, since enqueue() bursts dont have
effect on dequeue() rate.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 984c1b0..fc12fe6 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -574,7 +574,6 @@
 	}
 
 	sch->q.qlen++;
-	qdisc_bstats_update(sch, skb);
 	return NET_XMIT_SUCCESS;
 }
 
@@ -842,7 +841,7 @@
 
 static struct sk_buff *htb_dequeue(struct Qdisc *sch)
 {
-	struct sk_buff *skb = NULL;
+	struct sk_buff *skb;
 	struct htb_sched *q = qdisc_priv(sch);
 	int level;
 	psched_time_t next_event;
@@ -851,6 +850,8 @@
 	/* try to dequeue direct packets as high prio (!) to minimize cpu work */
 	skb = __skb_dequeue(&q->direct_queue);
 	if (skb != NULL) {
+ok:
+		qdisc_bstats_update(sch, skb);
 		sch->flags &= ~TCQ_F_THROTTLED;
 		sch->q.qlen--;
 		return skb;
@@ -884,11 +885,8 @@
 			int prio = ffz(m);
 			m |= 1 << prio;
 			skb = htb_dequeue_tree(q, prio, level);
-			if (likely(skb != NULL)) {
-				sch->q.qlen--;
-				sch->flags &= ~TCQ_F_THROTTLED;
-				goto fin;
-			}
+			if (likely(skb != NULL))
+				goto ok;
 		}
 	}
 	sch->qstats.overlimits++;